IBMDOS.COM

IBMDOS.COM is the filename of the DOS kernel. Loaded and initially invoked by the DOS BIOS in IBMBIO.COM during the boot process,^[1] it contains the hardware-independent parts of the operating system, including the embedded FAT12, FAT16 and, in newer versions, the FAT32 file system code, as well as the code to provide the DOS API to applications.

The file exists in PC DOS 1.0 to 7.10 and DR DOS 5.0 and higher^[2] (except for DR-DOS 7.06), with MS-DOS using MSDOS.SYS (from version 1.10 to 6.22) for the same purpose. DR DOS 3.31 to 3.41 used the equivalent DRBDOS.SYS file instead.^[2]^[1] (For compatibility purposes with some DOS applications the IBMDOS.COM file name was briefly also used by the IBM version of OS/2 1.0, where it resembled the OS2DOS.COM OS/2 kernel file as used by Microsoft.)

By default, the file is located in the root directory of the bootable drive/partition (normally C:\) and has the hidden, read-only, and system file attributes set.^[2] As IBMDOS.COM is a binary image containing executable code rather than a true COM-style program, the hidden attribute is set to keep the file from being accidentally invoked at the command prompt, which would lead to a crash. This is not necessary for DR-DOS 7.02 and higher, because under these systems the file is a fat binary also containing a tiny COM-style stub just displaying some version info and exiting gracefully when loaded inappropriately.^[3]^[1]

In Digital Research terminology, the kernel component of the operating system is called the BDOS (Basic Disk Operating System),^[1] a term originally coined by Gary Kildall in 1975 for CP/M,^[4] but which is continued to be used in all other DRI operating systems (except for Concurrent DOS 286 and FlexOS). Microsoft has used this name as well when referring to the kernel of the MSX-DOS operating system. The FAT file system specific code is called the FDOS in DRI terminology.

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References

^ ^a ^b ^c ^d Paul, Matthias R. (1997-10-02) [1997-09-29]. "Caldera OpenDOS 7.01/7.02 Update Alpha 3 IBMBIO.COM - README.TXT and BOOT.TXT - A short description of how OpenDOS is booted". Archived from the original on 2003-10-04. Retrieved 2009-03-29. [1]
^ ^a ^b ^c Paul, Matthias R. (2017-08-14) [2017-08-07]. "The continuing saga of Windows 3.1 in enhanced mode on OmniBook 300". MoHPC - the Museum of HP Calculators. Archived from the original on 2017-10-06. Retrieved 2017-10-06. […] In case no source drive and path is given, SYS will assume the system files to reside on the drive containing the SYS.COM program. If this is a local drive, it will try to locate them in the root of this drive, otherwise it will search for them in the SYS.COM directory itself. […] /K Keep original attributes of system files (else set to +RSH). […] /3 or /5 Name either DRBIOS.SYS/DRBDOS.SYS or IBMBIO.COM/IBMDOS.COM. […]
^ DR-DOS 7.03 WHATSNEW.TXT - Changes from DR-DOS 7.02 to DR-DOS 7.03. Caldera, Inc. 1998-12-24. Archived from the original on 2019-04-08. Retrieved 2019-04-08.

^ Kildall, Gary Arlen (June 1975), CP/M 1.1 or 1.2 BIOS and BDOS for Lawrence Livermore Laboratories, An excerpt of the BDOS.PLM file header in the PL/M source code of CP/M 1.1 or CP/M 1.2 for Lawrence Livermore Laboratories (LLL):

[…]
/* C P / M   B A S I C   I / O    S Y S T E M    (B I O S)
                    COPYRIGHT (C) GARY A. KILDALL
                             JUNE, 1975                   */
[…]
/*  B A S I C   D I S K    O P E R A T I N G   S Y S T E M  (B D O S)
                    COPYRIGHT (C) GARY A. KILDALL
                            JUNE, 1975                          */
[…]

Disk operating systems (DOS)

MS-DOS, IBM PC DOS,
compatible systems