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From Wikipedia, the free encyclopedia

Computer
Computers and computing devices from different eras

A computer is a device that can be instructed to carry out arbitrary sequences of arithmetic or logical operations automatically. The ability of computers to follow generalized sets of operations, called programs, enables them to perform an extremely wide range of tasks.

Such computers are used as control systems for a very wide variety of industrial and consumer devices. This includes simple special purpose devices like microwave ovens and remote controls, factory devices such as industrial robots and computer assisted design, but also in general purpose devices like personal computers and mobile devices such as smartphones. The Internet is run on computers and it connects millions of other computers.

Since ancient times, simple manual devices like the abacus aided people in doing calculations. Early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century. The first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then.

Conventionally, a modern computer consists of at least one processing element, typically a central processing unit (CPU), and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices include input devices (keyboards, mice, joystick, etc.), output devices (monitor screens, printers, etc.), and input/output devices that perform both functions (e.g., the 2000s-era touchscreen). Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved.

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  • Assembly and Review - PE6502 Hobby Computer
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Transcription

Hello, and welcome back to The 8-Bit Guy. So, in this episode, I’m going to assemble the PE6502 computer. This is a hobbyist computer that’s meant to be assembled at home, and this is actually a prototype. This computer is supposed to be Apple 1 compatible so you should be able to run Apple 1 software on it and BASIC and stuff like that. However, I spent a couple of hours talking with Jason on the phone, he’s the guy that designed this. And he said he likes to call it Apple 1.5 compatible. Because it’s a bit more powerful than an Apple 1 but now quite an Apple 2. But, what’s really interesting is that what he’s actually working on now is making some changes that will allow this to run Commodore BASIC. And have the entire Commodore screen editor and everything, which I think would be really cool. So, but I’m going to go ahead and put this one together and see what I can get running on it. I’ll hook it up to my little handy TV here and I don’t know, let’s assemble it and see if we can make it work!bThese zip-lock bags should have all of the components to build this computer. Let’s take them out and have a look at them. I’m not sure if there is any rhyme or reason to the way these are packaged. Some things are grouped together in bags. It looks like all of the smaller components are in this bag. Here’s the actual board. It’s really nice and well made. That’s definitely a lot of parts to solder! Well, I guess I had better get out the soldering station and all of my tools. But I also decided to print out the manual as it was difficult to reference it quickly on my computer. It’s quite a few pages, so I printed it double sided to make it easier to manage. All right, so I’ve got my soldering iron, I’ve got the manual, and the board here. I also need a multi meter. One of the main reasons I need the multi meter is for all of these resistors, because guess what? I can’t read the codes on these resistors. It’s great that he even included the color charts for the resistors, but the problem is I’m color blind and can rarely distinguish brown from green or violet from blue. I can see most of the other colors in the spectrum, but it’s really hard for me to see brown and violet. So, I can use the meter to measure the resistors so I make sure I use the right ones in the right places. It’s also handy to have a picture here of the final assembly because sometimes that’s more helpful than a diagram. I’m actually going to start with the resistors because they are the most challenging for me due to my color blindness and I’d just like to get them over with. And please don’t send me a million emails about those special sunglasses for colorblind people. Now, the good news is, a lot of these are fairly obvious which value they are even without the multi meter because I can tell that, hey, these 10 are obviously all of the same, and so I can look on the bill of materials and see there are 10 identical resistors here, so I know which ones these are. And the same with these 7 here. So that just leaves these for me to measure. So I’ll start with these 10 here, and the way I’m going to do this is just to use the bill of materials. So let’s look at all of these 1 kilo-ohm resistors and I’ll just start with this one which is R2. So I’ll just look on the board and I can clearly see R2 here. Pity there’s no D2, right? Then we’d have R2D2. Ha Ha. Anyway, that’s pretty much where all of those 1K resistors go. So I’ll put all of those in. Resistors are pretty easy to install. Just bend the leads over like this. It doesn’t really matter which direction they go in, but it is nice to try to put all of them the same direction so it looks professional. Once in the hole, I usually bend the leads out just a bit so it doesn’t fall back through while I’m soldering. I’m still waiting on my soldering station to warm up. I forgot to turn it on earlier. I’m using the default setting of 750 degrees. There we go, all ready! And, in case I’ve never mentioned this, soldering while trying to record it with a camera is actually really difficult because you’ve got to get just the right angle to see the action, and make sure your hands and other objects are out of the way. I’m often contorting my body to accommodate the tripod. So, doing this without filming is much easier. So, when you see me shaking it’s not because I am coming down with Parkinson’s disease, it’s simply because I’m probably in an awkward position when I’m trying to record it. OK, this is what good solder joints should look like. Afterwords, you can use some cutters to remove the excess leads. So, now I just have a bunch more resistors to do. Every time I put in a component, I mark it off the list so I know it’s done. All right, so I’ve managed to install all of these resistors here and over here just by using reasoning without having to measure anything or being able to read the codes. These are all that’s left and I’ll have to measure them. OK fast forward a bit, and I’ve done all of the resistors now. Notice I put them all in the same direction, which makes it look nicer. For me, this was the most apprehensive part of this project, so everything else should be a piece of cake! The next challenge is going to be all of these tiny capacitors. Now the thing is, the text on these guys is really small. And my 42 year old eyes cannot read anything this small anymore. So I’ll be using this magnifying glass. This one is really handy because it has a built in LED light. Anyway, as you can see, it will bring these numbers into sharp focus, even for me! The good news is, these capacitors are apparently all the same values. The bad news is, they don’t fit quite right into the holes. The leads are too close together. So that’s about as far down as it wants to slide. This is not uncommon, actually. The solution is to bend the leads a bit like this. And so, yeah, it will go in a lot further now. And so that’s how it looks after being soldered in place. It’s not perfect, but it will work. And so here’s all of the little capacitors now finished. Next up is this resistor pack. Basically it has 6 identical resistors inside which share a common lead. And if you see that little dot on the left, that represents pin 1. And if you look on the board here, pin one is also labeled so you know which direction to put this. So we’ll just stick that in there, and solder that from the other side. You sort of need 3 hands to install one of these, but the way I usually do this is I hold the resistor pack from the other side with one hand, then I’ll bend my lead of solder out so it sort of holds itself near the place I need to solder like this, and just bring the whole board to the solder. All I need to do is get one pin soldered so that it will hold it in place. Then the rest of the pins are easy to do. I should mention, by the way, that I tend to like to install low-profile parts on a board first, before I install any taller parts. So that’s just my preference, but it seems to make it easier because the board will lay mostly flat and also because the smaller parts won’t get in the way of the big parts when it is time to insert them. All right, so the next part I’m going to install is this 1 Mhz oscillator. This is what runs the clock on the 6502 processor. You may be wondering how to tell which direction it goes. Well, if you look, there’s this little circle here, that represents pin 1. And of course, pin 1 is clearly marked on the board. So it just goes in nice and easy, like this. After soldering, these are a bit too long, so I’m going to cut them off. And next up is the 5 Mhz Crystal used for the Parallax Propeller chip. This has no specific orientation, you can put it in either direction. And this fits in nice and flat. There’s exactly one diode in this project, and here it is. There’s a stripe on the right side, which indicates the polarity. The good news is, this board is labelled really well. Notice D1, that’s where the diode goes and there’s a little stripe on the diagram. This will be pretty similar to the resistor in that the leads get bent like so. And then right down it goes! There’s also exactly one transistor in this build. Now, the only thing you need to know in this case, is that the transistor has a flat side. If you look at the board, it goes right there, labelled Q1. And you can clearly see the flat side. The problem is the center lead will need to be bent out some. So I usually just bend the lead out like this. Then I’ll use some needle nose pliers to bent it back down like this. So now, it should fit in there better. Yeah, actually it fits great! So, I’ll check that off the list. Moving on, the next thing are these two momentary switches, used for reset switches. One of them goes here, for resetting the propeller chip, and the other goes over here for resetting the CPU. Now, these look kind of square like they might go in more than one direction, but they are actually slightly rectangular and will only fit one direction, so don’t worry about that. Once it is lined up, it does take a bit of force to pop it down. The next thing I’m going to solder in is this pin header. Now, I will warn you that these are copper all the way from one side to the other. So if you are holding this from one side while you solder it from the other, it will conduct the heat really well and you’re going to burn your finger. So, this goes right here. I suggest you be very aware which pins you are touching when you go to solder this in! Of course, once you get the first pin soldered, the rest of them are easy to do. Next up, I’m going to start installing the sockets, starting with these little ones. With any socket, be sure to double check this little notch and make sure it lines up with a similar looking notch on the board. OK, so fast forwarding a bit, I’ve got that one installed, and that one installed, however, I’ve got all of these sockets left to do. These are going to be some of the most time consuming parts to install. I tend to hold these with one hand, and I do sort of like I did with the resistor pack, where I just put the solder right where I need it to get that first pin done. Once that’s done, I turn the board around and solder the opposite pin on that socket. OK, so I’ve got each corner soldered. And these aren’t even very good solder joints. But that’s okay because they will hold it in place long enough for me to get some other pins soldered. At this point, I just want to double check the board from all directions that the socket is in flat and that it is facing the right direction. This would be a real pain to fix later. Now I can solder the rest of the pins. I’ll take this opportunity to mention that I wouldn’t really suggest a board like this for your very first soldering project. I’d suggest something smaller and cheaper. But if you’re a bit inexperienced, doing a board like this is going to give you a lot of practice. I would also like to mention I get a lot of requests to make a tutorial on how to solder. But, honestly, there are several other youtube channels that have that covered pretty well. I usually recommend a video by EEVBlog, which I think covers about everything you need to know. I will also mention that I’m using lead-based solder, which in my opinion is easier to work with and does a better job. However, I do have a fan going in the room that helps to blow the fumes away from my face. I also always wash my hands when I’m done soldering to remove any residue from my hands. And some people might wonder why anyone would want to assemble this stuff on their own. Well, to be honest, that’s half of the fun of a project like this. It’s sort of like a jig-saw puzzle for nerds. It will take you a few hours to assemble this and then there’s the anticipation of whether or not it will work when it is done! OK, so I’ve got a problem. These are the only pieces I have left, and I am missing a socket, which goes right here for the MAX232, which is the serial port controller. So, I guess what I’m going to do is just solder that chip in directly. Which, is fine. I mean, you don’t have to have a socket. The main benefit of a socket is to make it easy to remove if you fry the chip or for whatever reason you might want to remove it. But we have sockets for all of the rest of the chips, so I think we’ll be fine. OK, so now I’m going to start installing some of the taller objects, such as this header for the system bus. One problem you might notice is that… he he, gee it’s too big to fit. So no problem. I’ll just use some cutters and cut it to the right size. And there we go, fits perfectly now! Next I’ll do the PS/2 keyboard connector. PS/2 is kind of obsolete now, but at least they were made in the millions so they should still be pretty easy to find. Anyway, so that goes on like so. And this is the next thing I’m going to put in. This is the composite video connector. This is where the TV or monitor will connect. This thing has some pretty big pins on it, that’s to help with the stress of plugging and unplugging those cables. And the last of the connectors is the DC power port, which is a fairly standard barrel connector. I should mention this kit does not come with a power supply. Anyway, so the connector goes here. Like so. And this thing also has some rather large pins to help with the stress of connecting and disconnecting those cables. I can’t tell you how many laptops I’ve seen in my life that had broken power ports, usually because somebody tripped over the wire. Moving along, this is the power LED. Now, you’ll notice that one leg here is longer than the other. And that is the positive lead. And when you look on the board, you’ll notice a flat side, and that is for the negative. So the shorter leg will go in that side, like so. Next up are two voltage regulators. One of these is for 5 volts for the 6502, and then a 3.3 volt version for the propeller chip. Just line up the flat side with the big white line there. Easy peasy. One of the last things left to do is install these electrolytic capacitors. I’m going to start with this big one here. These do have a specific polarity so you need to make sure you don’t put them in backwards. You’ll notice there is a stripe on this one side here. And that needs to line up with the stripe on the board. Now this board is different from any other I’ve seen when it comes to electrolytic caps. So, this cap goes in C21, but it is drawn as a square on the board. I’m thinking maybe he originally planned to use tantalum capacitors or something. Anyway, there is clearly a line showing where the stripe goes so you can still line it up. But, it fits in there perfectly. I’ll bend the leads out to make it easier to solder. And the soldering is almost done for this job. Notice there’s this spot to solder in a switch, but no switch was actually included in the kit. This is if you wanted to add your own to whatever case you might mount this in. For me, I’m just going to use some of these left over pins and solder those in. Skipping ahead, those are in now, and I’ll just use this jumper here to act as a switch so that power is always on whenever the plug is inserted. This would also make it really easy to connect a power switch in the future. And here’s all of the left over trash and excess leads from assembly. Now, the only thing that is left is to take all of these chips and insert them into the sockets. So, let’s get started! I’m going to start with the 6502. Believe it or not, this is a brand new chip, Western Digital still makes these, although I have no idea what uses them these days. But this is definitely the newest 6502 I’ve ever held in my hands. Now I’m going to put this in the socket. I’ve actually bent the pins in just slightly to help them line up. It’s very important to make sure these pins are lined up really well, otherwise when you go to push it down, one or more pins could bend or break off. Same thing goes for these smaller chips, also be sure to double check the direction and line up the notch! This is the firmware ROM chip. Let’s put this in! It takes a surprising amount of force to push these things in. Next up is the propeller chip which will serve as a video display since you can no longer buy the original Apple 1 video chips. And this is a static RAM chip, I believe 32K, which is a lot more than the 4K of the original Apple 1. And THIS is a perfect example of pins not cooperating when I tried to insert the chip. Fortunately, I caught it before I pushed it all the way down, so I can pull this out and bend them back. OK, so this thing is finally finished. All that is left to do is test it! I’m going to need a power supply. I hope this is going to work. It has the right connector and it’s actually 6.5 volts, even though the instructions call for 9V, this should actually work because it’s rated for anything between 6.5 and 9 volts. This actually comes from my speak and spell. Anyway, I think it’s going to work. And of course, we’ll need a standard composite video cable. And I’m going to use this old PS/2 keyboard. It’s the perfect size for this project. So I’ll plug in the keyboard, and then I’ll plug in the composite video cable. And now it is time for the smoke test. If I did anything catastrophically wrong, this is when I’ll find out. Well, the good news is, nothing smoked or popped. The bad news is, there’s no video display. The power LED did come on, though. OK, so I am not terribly surprised that it didn’t work. In fact, I would have been more surprised if it had worked the first time. There’s always some little detail an an assembly like this that’s going to keep something from working, even the tiniest little thing can keep it from booting. But, you know I’m pretty sure I can get this to work. So, I’m going to go ahead and start some of my standard troubleshooting techniques. The first thing I wanted to do is check the voltage at one of the chips to make sure we’re getting a steady 5V. And we are. So the power supply and regulator and all of that is working fine. The next thing I did was swap out this serial eprom for the propeller chip. He sent me two of these for some reason, so let me try the second one. And behold! It actually works. Well, sort of. I entered into BASIC and just wanted to type something, sure syntax error, that’s expected. But then I discovered that any command I typed gave me a syntax error. In fact, pretty much nothing worked right on this board. It was very unstable! It would reboot constantly like every few seconds, most commands I would type would either give strange results or just cause the computer to reboot. So, I knew something wasn’t right. I knew there had to be some other problem and I spent a lot of time troubleshooting the board, and I couldn’t really find anything wrong. Now, the manual had said in here to clean all of the excess flux off the bottom of the board and that is something I had intended to do. But, you know, I was kind of in a hurry so I just thought, I’ll skip that step for now and I didn’t realize how important of a step that is because flux apparently is conductive. And, I guess that never really occurred to me. But yeah, so I took some alcohol and a toothbrush and I spent some time scrubbing the flux off of the board and then I actually rinsed it in the sink and then it had to dry for a little while, actually had to let it dry for several hours even after I used some compressed air to blow all of the water off. But after that, I turned it on, and it actually works perfectly! It’s perfectly stable now! So, let’s take a tour and see what we can do with this thing! So, it boots up into something called wozmon, which stands for Wozniak Monitor. It’s a really simple operating system. Just for some examples of what you can do. If I type a memory address, like 2000, it will simply reply and tell me what byte is stored at that address, in this case FC. Of course this is all in hexadecimal. If I wanted to see a large chunk of memory, I can type the address, then a period, and then another address. Then it will show me everything that is between those addresses. There are two versions of BASIC stored in ROM, so I can start one of those up by typing the starting address followed by an R. So, now I’m in integer BASIC. Of course, I’m actually more comfortable in Applesoft BASIC, so I’ll use that one instead. Of course, when demonstrating BASIC, everyone has to write a small looping command to print something down the screen. So I won’t disappoint. However, I’ll write something maybe a little bit more interesting. This is called a random maze. We used to make these on the Commodore VIC-20 and 64. It doesn’t look quite as good here because the lines don’t actually touch each other, but you can still see the maze if you concentrate. So you may be wondering what else you can do with it, since there are no disk drives or SD card sockets or any way to copy over any other programs. The original Apple 1 at least had a cassette port interface. This doesn’t even have that. The only way to actually get new programs onto this computer is to type them in with the keyboard either in BASIC or in machine code. However, it does have a serial port, which can make that a lot easier. So I’ll just connect it up to one of my old MS-DOS laptops. I was going to use my favorite terminal program, Telix, however, it doesn’t seem to want to run on this laptop. So I’ll just use Hyperterminal inside of Windows 95 instead. According to the manual it needs to be set to 115,200 bits per second. And it’s working, because that READY is coming from the little computer. OK, so what I’m going to do now is click transfer and send a text file over the serial port. I’m going to pick microchess. As soon as I do this, you’ll see this machine language code flying down the screen. As far as the computer is concerned, somebody is typing this in on the keyboard. It just so happens, the thing typing it is another computer, so it’s really fast! Once it’s done, it automatically starts the game, as that’s the last command in the text file. I’ve never played this before, so I’m not sure how it works. I’ll pick zero, I guess. I have no idea what this means either. And I can’t figure out what I’m doing here either. I guess somehow I’m supposed to indicate which piece I want to move. Anyway, I’ll have to read up on that later. Moving on, you can also send BASIC programs much in the same way. First, you just go into BASIC, in this case Applesoft Basic, and I’ll send over a text file for hangman. Again, it’s like I’m typing in the hangman game really fast. However, when it is done, it errors out. So I’m thinking maybe it was designed for integer BASIC instead, so I’ll change over to that version and then try it again. Skipping ahead a bit… it works. I’ll guess E, nope.. how about S, nope. U, maybe R, T, dang.. what is this? Well, after nearly trying the whole alphabet, it turned out to be FLY. Lovely. Anyway, let’s try another one. This is checkers. Again, I can’t quite figure out the commands on this without reading the manual, so I’ll do that later. All right, so I was not super impressed with any of the games that are available for this little computer, so I thought I’ll just write my own. I was kind of thinking something along the lines of Tetris. I figure I could probably write that in a few hours if I didn’t try to get too fancy. The trouble is, I couldn’t figure out how to address the screen memory. And documentation for the Apple 1 is a bit scarce and when you type that into google you always get results for the Apple I devices like iPhones and iPads and stuff like that. Eventually, with enough asking around I finally did find some documentation and one of the things I discovered about the Apple 1 design which is really bizarre is that it’s impossible to actually address characters like anywhere on the screen you want. So, the only thing that this computer can do is it can send characters one at a time to a screen controller which will place the characters at the bottom of the screen and then scroll everything else up. But, it’s actually impossible to come back up here and change some character that’s already on the screen. The system’s simply just not capable of doing that. And, to illustrate why, I want to show you this little diagram, king of showing a rough bus design of a traditional 8-bit computer that would have been made during the 1980s. In a typical system of the 1980s, the CPU would talk with a peripheral interface adapter, and that’s usually what connects to things like keyboards, joysticks, and disk drives. And then there’s the ROM and RAM on the same bus with the CPU. And then the video chip usually shares some of the RAM, and displays whatever it reads on an external monitor. The apple 1, however, has no joystick, no disk drive, and to be honest, no video chip. At least not in the traditional sense. What it does have is a rudimentary terminal display like you’d find in a dumb terminal of the 70s. And it is connected to the PIA chip, and the CPU just sends characters over to be displayed. But the CPU has absolutely no control as to where on the screen the character will end up. That’s all handled by those terminal chips. Which means, coding a simple program like Tetris is essentially impossible on the Apple 1. In fact, that explains a lot as to why those programs like the chess would always redraw the entire board every time you make a move. So that really limits what you can do with a computer like this. However, it does have the full system bus available here on this pin header, so there’s no reason you couldn’t attach some other kind of video chip, or even a little LCD screen like this. In fact, I may mess with getting one of these working for a future episode. But still, you know it’s a neat little computer, and especially with the expansion socket that I mentioned, you could hack all kinds of things on there. I mean heck, I bet you could get a SID chip to work on there if you wanted to! But, I’ll be much more impressed when somebody creates something really similar to this that can run Commodore BASIC. You know, the actually screen editor, and BASIC, and the Commodore kernel. And it doesn’t have to be compatible with the Commodore 64 or VIC-20, as long as it can just run those things so that you can get the environment and you know you could probably port over a lot of existing software, so that’s something that I would have a lot of fun playing with. But, I do think it definitely needs and SD-card socket so that you can load and save programs to something at least a little bit more modern. I’d probably try to design it myself, but I simply don’t have the time and it’s probably a little bit beyond my abilities. Still, if anybody else has a neat little home-brew kit like this they’d like to send me, please, contact me and tell me about it and you know, I may feature it here on the show in some future episode. Otherwise, I guess that about wraps it up for this one, so stick around and thanks for watching!

Contents

Etymology

According to the Oxford English Dictionary, the first known use of the word "computer" was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: "I haue [sic] read the truest computer of Times, and the best Arithmetician that euer [sic] breathed, and he reduceth thy dayes into a short number." This usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. From the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations.[1]

The Online Etymology Dictionary gives the first attested use of "computer" in the "1640s, [meaning] "one who calculates,"; this is an "... agent noun from compute (v.)". The Online Etymology Dictionary states that the use of the term to mean "calculating machine" (of any type) is from 1897." The Online Etymology Dictionary indicates that the "modern use" of the term, to mean "programmable digital electronic computer" dates from "... 1945 under this name; [in a] theoretical [sense] from 1937, as Turing machine".[2]

History

Pre-20th century

Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick. Later record keeping aids throughout the Fertile Crescent included calculi (clay spheres, cones, etc.) which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers.[3][4] The use of counting rods is one example.

 The Chinese Suanpan (算盘) (the number represented on this abacus is 6,302,715,408)
The Chinese Suanpan (算盘) (the number represented on this abacus is 6,302,715,408)

The abacus was initially used for arithmetic tasks. The Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Since then, many other forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, and markers moved around on it according to certain rules, as an aid to calculating sums of money.

 The ancient Greek-designed Antikythera mechanism, dating between 150 and 100 BC, is the world's oldest analog computer.
The ancient Greek-designed Antikythera mechanism, dating between 150 and 100 BC, is the world's oldest analog computer.

The Antikythera mechanism is believed to be the earliest mechanical analog "computer", according to Derek J. de Solla Price.[5] It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later.

Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century.[6] The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer[7][8] and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235.[9] Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe,[10] an early fixed-wired knowledge processing machine[11] with a gear train and gear-wheels,[12] circa 1000 AD.

The sector, a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation.

The planimeter was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage.

 A slide rule
A slide rule

The slide rule was invented around 1620–1630, shortly after the publication of the concept of the logarithm. It is a hand-operated analog computer for doing multiplication and division. As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as transcendental functions such as logarithms and exponentials, circular and hyperbolic trigonometry and other functions. Slide rules with special scales are still used for quick performance of routine calculations, such as the E6B circular slide rule used for time and distance calculations on light aircraft.

In the 1770s Pierre Jaquet-Droz, a Swiss watchmaker, built a mechanical doll (automata) that could write holding a quill pen. By switching the number and order of its internal wheels different letters, and hence different messages, could be produced. In effect, it could be mechanically "programmed" to read instructions. Along with two other complex machines, the doll is at the Musée d'Art et d'Histoire of Neuchâtel, Switzerland, and still operates.[13]

The tide-predicting machine invented by Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.

The differential analyser, a mechanical analog computer designed to solve differential equations by integration, used wheel-and-disc mechanisms to perform the integration. In 1876 Lord Kelvin had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators.[14] In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The torque amplifier was the advance that allowed these machines to work. Starting in the 1920s, Vannevar Bush and others developed mechanical differential analyzers.


First computing device

Charles Babbage, an English mechanical engineer and polymath, originated the concept of a programmable computer. Considered the "father of the computer",[15] he conceptualized and invented the first mechanical computer in the early 19th century. After working on his revolutionary difference engine, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an Analytical Engine, was possible. The input of programs and data was to be provided to the machine via punched cards, a method being used at the time to direct mechanical looms such as the Jacquard loom. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. The Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete.[16][17]

The machine was about a century ahead of its time. All the parts for his machine had to be made by hand — this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the British Government to cease funding. Babbage's failure to complete the analytical engine can be chiefly attributed to difficulties not only of politics and financing, but also to his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Nevertheless, his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906.

Analog computers

 Sir William Thomson's third tide-predicting machine design, 1879–81
Sir William Thomson's third tide-predicting machine design, 1879–81

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.[18] The first modern analog computer was a tide-predicting machine, invented by Sir William Thomson in 1872. The differential analyser, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson, the brother of the more famous Lord Kelvin.[14]

The art of mechanical analog computing reached its zenith with the differential analyzer, built by H. L. Hazen and Vannevar Bush at MIT starting in 1927. This built on the mechanical integrators of James Thomson and the torque amplifiers invented by H. W. Nieman. A dozen of these devices were built before their obsolescence became obvious. By the 1950s the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education (control systems) and aircraft (slide rule).

Digital computers

Electromechanical

By 1938, the United States Navy had developed an electromechanical analog computer small enough to use aboard a submarine. This was the Torpedo Data Computer, which used trigonometry to solve the problem of firing a torpedo at a moving target. During World War II similar devices were developed in other countries as well.

 Replica of Zuse's Z3, the first fully automatic, digital (electromechanical) computer.
Replica of Zuse's Z3, the first fully automatic, digital (electromechanical) computer.

Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer.[19]

In 1941, Zuse followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully automatic digital computer.[20][21] The Z3 was built with 2000 relays, implementing a 22 bit word length that operated at a clock frequency of about 5–10 Hz.[22] Program code was supplied on punched film while data could be stored in 64 words of memory or supplied from the keyboard. It was quite similar to modern machines in some respects, pioneering numerous advances such as floating point numbers. Rather than the harder-to-implement decimal system (used in Charles Babbage's earlier design), using a binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.[23] The Z3 was Turing complete.[24][25]

Vacuum tubes and digital electronic circuits

Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer Tommy Flowers, working at the Post Office Research Station in London in the 1930s, began to explore the possible use of electronics for the telephone exchange. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes.[18] In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff–Berry Computer (ABC) in 1942,[26] the first "automatic electronic digital computer".[27] This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory.[28]

 Colossus was the first electronic digital programmable computing device, and was used to break German ciphers during World War II.
Colossus was the first electronic digital programmable computing device, and was used to break German ciphers during World War II.

During World War II, the British at Bletchley Park achieved a number of successes at breaking encrypted German military communications. The German encryption machine, Enigma, was first attacked with the help of the electro-mechanical bombes. To crack the more sophisticated German Lorenz SZ 40/42 machine, used for high-level Army communications, Max Newman and his colleagues commissioned Flowers to build the Colossus.[28] He spent eleven months from early February 1943 designing and building the first Colossus.[29] After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944[30] and attacked its first message on 5 February.[28]

Colossus was the world's first electronic digital programmable computer.[18] It used a large number of valves (vacuum tubes). It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete. Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both 5 times faster and simpler to operate than Mark I, greatly speeding the decoding process.[31][32]

 ENIAC was the first electronic, Turing-complete device, and performed ballistics trajectory calculations for the United States Army.
ENIAC was the first electronic, Turing-complete device, and performed ballistics trajectory calculations for the United States Army.

The U.S.-built ENIAC[33] (Electronic Numerical Integrator and Computer) was the first electronic programmable computer built in the US. Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was Turing-complete. Like the Colossus, a "program" on the ENIAC was defined by the states of its patch cables and switches, a far cry from the stored program electronic machines that came later. Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches.

It combined the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words (about 80 bytes). Built under the direction of John Mauchly and J. Presper Eckert at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors.[34]

Modern computers

Concept of modern computer

The principle of the modern computer was proposed by Alan Turing in his seminal 1936 paper,[35] On Computable Numbers. Turing proposed a simple device that he called "Universal Computing machine" and that is now known as a universal Turing machine. He proved that such a machine is capable of computing anything that is computable by executing instructions (program) stored on tape, allowing the machine to be programmable. The fundamental concept of Turing's design is the stored program, where all the instructions for computing are stored in memory. Von Neumann acknowledged that the central concept of the modern computer was due to this paper.[36] Turing machines are to this day a central object of study in theory of computation. Except for the limitations imposed by their finite memory stores, modern computers are said to be Turing-complete, which is to say, they have algorithm execution capability equivalent to a universal Turing machine.

Stored programs

Three tall racks containing electronic circuit boards
A section of the Manchester Small-Scale Experimental Machine, the first stored-program computer.

Early computing machines had fixed programs. Changing its function required the re-wiring and re-structuring of the machine.[28] With the proposal of the stored-program computer this changed. A stored-program computer includes by design an instruction set and can store in memory a set of instructions (a program) that details the computation. The theoretical basis for the stored-program computer was laid by Alan Turing in his 1936 paper. In 1945 Turing joined the National Physical Laboratory and began work on developing an electronic stored-program digital computer. His 1945 report "Proposed Electronic Calculator" was the first specification for such a device. John von Neumann at the University of Pennsylvania also circulated his First Draft of a Report on the EDVAC in 1945.[18]

The Manchester Small-Scale Experimental Machine, nicknamed Baby, was the world's first stored-program computer. It was built at the Victoria University of Manchester by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948.[37] It was designed as a testbed for the Williams tube, the first random-access digital storage device.[38] Although the computer was considered "small and primitive" by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer.[39] As soon as the SSEM had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1.

The Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world's first commercially available general-purpose computer.[40] Built by Ferranti, it was delivered to the University of Manchester in February 1951. At least seven of these later machines were delivered between 1953 and 1957, one of them to Shell labs in Amsterdam.[41] In October 1947, the directors of British catering company J. Lyons & Company decided to take an active role in promoting the commercial development of computers. The LEO I computer became operational in April 1951[42] and ran the world's first regular routine office computer job.

Transistors

The bipolar transistor was invented in 1947. From 1955 onwards transistors replaced vacuum tubes in computer designs, giving rise to the "second generation" of computers. Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat. Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space.

At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of valves.[43] Their first transistorised computer and the first in the world, was operational by 1953, and a second version was completed there in April 1955. However, the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read and write on its magnetic drum memory, so it was not the first completely transistorized computer. That distinction goes to the Harwell CADET of 1955,[44] built by the electronics division of the Atomic Energy Research Establishment at Harwell.[44][45]

Integrated circuits

The next great advance in computing power came with the advent of the integrated circuit. The idea of the integrated circuit was first conceived by a radar scientist working for the Royal Radar Establishment of the Ministry of Defence, Geoffrey W.A. Dummer. Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in Washington, D.C. on 7 May 1952.[46]

The first practical ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor.[47] Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958.[48] In his patent application of 6 February 1959, Kilby described his new device as "a body of semiconductor material ... wherein all the components of the electronic circuit are completely integrated".[49][50] Noyce also came up with his own idea of an integrated circuit half a year later than Kilby.[51] His chip solved many practical problems that Kilby's had not. Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby's chip was made of germanium.

This new development heralded an explosion in the commercial and personal use of computers and led to the invention of the microprocessor. While the subject of exactly which device was the first microprocessor is contentious, partly due to lack of agreement on the exact definition of the term "microprocessor", it is largely undisputed that the first single-chip microprocessor was the Intel 4004,[52] designed and realized by Ted Hoff, Federico Faggin, and Stanley Mazor at Intel.[53]

Mobile computers become dominant

With the continued miniaturization of computing resources, and advancements in portable battery life, portable computers grew in popularity in the 2000s.[54] The same developments that spurred the growth of laptop computers and other portable computers allowed manufacturers to integrate computing resources into cellular phones. These so-called smartphones and tablets run on a variety of operating systems and have become the dominant computing device on the market, with manufacturers reporting having shipped an estimated 237 million devices in 2Q 2013.[55]

Types

Computers are typically classified based on their uses:

Based on uses

Based on sizes

Hardware

Video demonstrating the standard components of a "slimline" computer

The term hardware covers all of those parts of a computer that are tangible physical objects. Circuits, computer chips, graphic cards, sound cards, memory (RAM), motherboard, displays, power supplies, cables, keyboards, printers and "mice" input devices are all hardware.

History of computing hardware

First generation (mechanical/electromechanical) Calculators Pascal's calculator, Arithmometer, Difference engine, Quevedo's analytical machines
Programmable devices Jacquard loom, Analytical engine, IBM ASCC/Harvard Mark I, Harvard Mark II, IBM SSEC, Z1, Z2, Z3
Second generation (vacuum tubes) Calculators Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
Programmable devices Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark 1, Ferranti Pegasus, Ferranti Mercury, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third generation (discrete transistors and SSI, MSI, LSI integrated circuits) Mainframes IBM 7090, IBM 7080, IBM System/360, BUNCH
Minicomputer HP 2116A, IBM System/32, IBM System/36, LINC, PDP-8, PDP-11
Desktop Computer Programma 101, HP 9100
Fourth generation (VLSI integrated circuits) Minicomputer VAX, IBM System i
4-bit microcomputer Intel 4004, Intel 4040
8-bit microcomputer Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
16-bit microcomputer Intel 8088, Zilog Z8000, WDC 65816/65802
32-bit microcomputer Intel 80386, Pentium, Motorola 68000, ARM
64-bit microcomputer[56] Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64, ARMv8-A
Embedded computer Intel 8048, Intel 8051
Personal computer Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet PC, Wearable computer
Theoretical/experimental Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer

Other hardware topics

Peripheral device (input/output) Input Mouse, keyboard, joystick, image scanner, webcam, graphics tablet, microphone
Output Monitor, printer, loudspeaker
Both Floppy disk drive, hard disk drive, optical disc drive, teleprinter
Computer buses Short range RS-232, SCSI, PCI, USB
Long range (computer networking) Ethernet, ATM, FDDI

A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by buses, often made of groups of wires. Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a "1", and when off it represents a "0" (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits.

Input devices

When unprocessed data is sent to the computer with the help of input devices, the data is processed and sent to output devices. The input devices may be hand-operated or automated. The act of processing is mainly regulated by the CPU. Some examples of input devices are:

Output devices

The means through which computer gives output are known as output devices. Some examples of output devices are:

Control unit

 Diagram showing how a particular MIPS architecture instruction would be decoded by the control system
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system

The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into control signals that activate other parts of the computer.[57] Control systems in advanced computers may change the order of execution of some instructions to improve performance.

A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[58]

The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

  1. Read the code for the next instruction from the cell indicated by the program counter.
  2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
  3. Increment the program counter so it points to the next instruction.
  4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
  5. Provide the necessary data to an ALU or register.
  6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
  7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
  8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).

The sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program, and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer, which runs a microcode program that causes all of these events to happen.

Central processing unit (CPU)

The control unit, ALU, and registers are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Arithmetic logic unit (ALU)

The ALU is capable of performing two classes of operations: arithmetic and logic.[59] The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division, trigonometry functions such as sine, cosine, etc., and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers, albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?"). Logic operations involve Boolean logic: AND, OR, XOR, and NOT. These can be useful for creating complicated conditional statements and processing boolean logic.

Superscalar computers may contain multiple ALUs, allowing them to process several instructions simultaneously.[60] Graphics processors and computers with SIMD and MIMD features often contain ALUs that can perform arithmetic on vectors and matrices.

Memory

 Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.
Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595." The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (28 = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties:

RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and software that never changes, therefore the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.[61]

In more sophisticated computers there may be one or more RAM cache memories, which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

Input/output (I/O)

 Hard disk drives are common storage devices used with computers.
Hard disk drives are common storage devices used with computers.

I/O is the means by which a computer exchanges information with the outside world.[62] Devices that provide input or output to the computer are called peripherals.[63] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O. I/O devices are often complex computers in their own right, with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics.[citation needed] Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O. A 2016-era flat screen display contains its own computer circuitry.

Multitasking

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.[64] One means by which this is done is with a special signal called an interrupt, which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time". then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.[65]

Before the era of inexpensive computers, the principal use for multitasking was to allow many people to share the same computer. Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly, in direct proportion to the number of programs it is running, but most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run simultaneously without unacceptable speed loss.

Multiprocessing

 Cray designed many supercomputers that used multiprocessing heavily.
Cray designed many supercomputers that used multiprocessing heavily.

Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[66] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.

Software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. Software is that part of a computer system that consists of encoded information or computer instructions, in contrast to the physical hardware from which the system is built. Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer hardware and software require each other and neither can be realistically used on its own. When software is stored in hardware that cannot easily be modified, such as with BIOS ROM in an IBM PC compatible computer, it is sometimes called "firmware".

Operating systems

Operating system /System Software Unix and BSD UNIX System V, IBM AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
GNU/Linux List of Linux distributions, Comparison of Linux distributions
Microsoft Windows Windows 95, Windows 98, Windows NT, Windows 2000, Windows ME, Windows XP, Windows Vista, Windows 7, Windows 8, Windows 8.1, Windows 10
DOS 86-DOS (QDOS), IBM PC DOS, MS-DOS, DR-DOS, FreeDOS
Macintosh operating systems Classic Mac OS, macOS (previously OS X and Mac OS X)
Embedded and real-time List of embedded operating systems
Experimental Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library Multimedia DirectX, OpenGL, OpenAL, Vulkan (API)
Programming library C standard library, Standard Template Library
Data Protocol TCP/IP, Kermit, FTP, HTTP, SMTP
File format HTML, XML, JPEG, MPEG, PNG
User interface Graphical user interface (WIMP) Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM, Aqua
Text-based user interface Command-line interface, Text user interface
Application Software Office suite Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
Internet Access Browser, Email client, Web server, Mail transfer agent, Instant messaging
Design and manufacturing Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
Graphics Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
Audio Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
Software engineering Compiler, Assembler, Interpreter, Debugger, Text editor, Integrated development environment, Software performance analysis, Revision control, Software configuration management
Educational Edutainment, Educational game, Serious game, Flight simulator
Games Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
Misc Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager

Languages

There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.

Programming languages
Lists of programming languages Timeline of programming languages, List of programming languages by category, Generational list of programming languages, List of programming languages, Non-English-based programming languages
Commonly used assembly languages ARM, MIPS, x86
Commonly used high-level programming languages Ada, BASIC, C, C++, C#, COBOL, Fortran, PL/1, REXX, Java, Lisp, Pascal, Object Pascal
Commonly used scripting languages Bourne script, JavaScript, Python, Ruby, PHP, Perl

Application Software

Programs

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that some type of instructions (the program) can be given to the computer, and it will process them. Modern computers based on the von Neumann architecture often have machine code in the form of an imperative programming language. In practical terms, a computer program may be just a few instructions or extend to many millions of instructions, as do the programs for word processors and web browsers for example. A typical modern computer can execute billions of instructions per second (gigaflops) and rarely makes a mistake over many years of operation. Large computer programs consisting of several million instructions may take teams of programmers years to write, and due to the complexity of the task almost certainly contain errors.

Stored program architecture

 Replica of the Small-Scale Experimental Machine (SSEM), the world's first stored-program computer, at the Museum of Science and Industry in Manchester, England
Replica of the Small-Scale Experimental Machine (SSEM), the world's first stored-program computer, at the Museum of Science and Industry in Manchester, England

This section applies to most common RAM machine-based computers.

In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction.

Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time, with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. The following example is written in the MIPS assembly language:

  begin:
  addi $8, $0, 0           # initialize sum to 0
  addi $9, $0, 1           # set first number to add = 1
  loop:
  slti $10, $9, 1000       # check if the number is less than 1000
  beq $10, $0, finish      # if odd number is greater than n then exit
  add $8, $8, $9           # update sum
  addi $9, $9, 1           # get next number
  j loop                   # repeat the summing process
  finish:
  add $2, $8, $0           # put sum in output register

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in a fraction of a second.

Machine code

In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode; the command to multiply them would have a different opcode, and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from, each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program[citation needed], architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.

While it is possible to write computer programs as long lists of numbers (machine language) and while this technique was used with many early computers,[67] it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember – a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler.

 A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labeled "PROJ039" for identification purposes.
A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labeled "PROJ039" for identification purposes.

Programming language

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine code by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques.

Low-level languages

Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a smartphone or a hand-held videogame) cannot understand the machine language of an x86 CPU that might be in a PC.[68]

High-level languages/third generation language

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. Therefore, most practical programs are written in more abstract high-level programming languages that are able to express the needs of the programmer more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.[69] High level languages are less related to the workings of the target computer than assembly language, and more related to the language and structure of the problem(s) to be solved by the final program. It is therefore often possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.

Fourth-generation languages

Fourth-generation languages (4GL) are less procedural than 3G languages. The benefit of 4GL is that they provide ways to obtain information without requiring the direct help of a programmer.

Program design

Program design of small programs is relatively simple and involves the analysis of the problem, collection of inputs, using the programming constructs within languages, devising or using established procedures and algorithms, providing data for output devices and solutions to the problem as applicable. As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered. Large programs involving thousands of line of code and more require formal software methodologies. The task of developing large software systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of software engineering concentrates specifically on this challenge.

Bugs

 The actual first computer bug, a moth found trapped on a relay of the Harvard Mark II computer
The actual first computer bug, a moth found trapped on a relay of the Harvard Mark II computer

Errors in computer programs are called "bugs". They may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases, they may cause the program or the entire system to "hang", becoming unresponsive to input such as mouse clicks or keystrokes, to completely fail, or to crash. Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an exploit, code designed to take advantage of a bug and disrupt a computer's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.[70] Admiral Grace Hopper, an American computer scientist and developer of the first compiler, is credited for having first used the term "bugs" in computing after a dead moth was found shorting a relay in the Harvard Mark II computer in September 1947.[71]

Firmware

Firmware is the technology which has the combination of both hardware and software such as BIOS chip inside a computer. This chip (hardware) is located on the motherboard and has the BIOS set up (software) stored in it.

Networking and the Internet

 Visualization of a portion of the routes on the Internet
Visualization of a portion of the routes on the Internet

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems such as Sabre.[72] In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. The effort was funded by ARPA (now DARPA), and the computer network that resulted was called the ARPANET.[73] The technologies that made the Arpanet possible spread and evolved.

In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Unconventional computers

A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk. While popular usage of the word "computer" is synonymous with a personal electronic computer, the modern[74] definition of a computer is literally: "A device that computes, especially a programmable [usually] electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information."[75] Any device which processes information qualifies as a computer, especially if the processing is purposeful.[citation needed]

Unconventional computing

Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors. However, conceptually computational systems as flexible as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (billiard ball computer); an often quoted example.[citation needed] More realistically, modern computers are made out of transistors made of photolithographed semiconductors.

Future

There is active research to make computers out of many promising new types of technology, such as optical computers, DNA computers, neural computers, and quantum computers. Most computers are universal, and are able to calculate any computable function, and are limited only by their memory capacity and operating speed. However different designs of computers can give very different performance for particular problems; for example quantum computers can potentially break some modern encryption algorithms (by quantum factoring) very quickly.

Computer architecture paradigms

There are many types of computer architectures:

Of all these abstract machines, a quantum computer holds the most promise for revolutionizing computing.[76] Logic gates are a common abstraction which can apply to most of the above digital or analog paradigms. The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a minimum capability (being Turing-complete) is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity.

Artificial intelligence

A computer will solve problems in exactly the way it is programmed to, without regard to efficiency, alternative solutions, possible shortcuts, or possible errors in the code. Computer programs that learn and adapt are part of the emerging field of artificial intelligence and machine learning. Artificial intelligence based products generally fall into two major categories: rule based systems and pattern recognition systems. Rule based systems attempt to represent the rules used by human experts and tend to be expensive to develop. Pattern based systems use data about a problem to generate conclusions. Examples of pattern based systems include voice recognition, font recognition, translation and the emerging field of on-line marketing.

Professions and organizations

As the use of computers has spread throughout society, there are an increasing number of careers involving computers.

Computer-related professions
Hardware-related Electrical engineering, Electronic engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoengineering
Software-related Computer science, Computer engineering, Desktop publishing, Human–computer interaction, Information technology, Information systems, Computational science, Software engineering, Video game industry, Web design

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.

Organizations
Standards groups ANSI, IEC, IEEE, IETF, ISO, W3C
Professional societies ACM, AIS, IET, IFIP, BCS
Free/open source software groups Free Software Foundation, Mozilla Foundation, Apache Software Foundation

See also

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  74. ^ According to the Shorter Oxford English Dictionary (6th ed, 2007), the word computer dates back to the mid 17th century, when it referred to "A person who makes calculations; specifically a person employed for this in an observatory etc."
  75. ^ "Definition of computer". Thefreedictionary.com. Retrieved 29 January 2012. 
  76. ^ II, Joseph D. Dumas (2005). Computer Architecture: Fundamentals and Principles of Computer Design. CRC Press. p. 340. ISBN 9780849327490. 

Notes

External links

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