serial ports. 232 simpler DE-9 (io nowadays surprising DB-25) only since the 1984 AT [post-xt, IBM 5170, with a 286] still sh** and hate coz vslow& +-12v anyway - there is a 3-wire jack subset too, &yost unix 8p8c(eth) 'phoneplug', &a DC 37 pin version too: now that's not for 232 but another, with +-6v 'only' (still huge swing) and nice diffpairs; #shock#: it (yes, the already-37) needed a complementary de9 connector too to fit yet moar lulz like a second chan, and another over nine thousand ground lines! not even the C shell was long enough for 2 wires... ;-); and this one is depicted here. when they realized this ludicruous waste (misengineering? well, not: decades earlier.) is not going to be tolerated in the era of microchips and labor/assembly costs (*pin counts, lessstandard sizes, multiple conns etc typinoldtelcotimestotaldisregardformassmfgringsimplicity&chpness to bow to the vacuum-tube and mech tty legacy. d-sub tho is inherently expensive), they put out a B-shell version with 232 arrangement - it's worthy to compare 'em (ie, the 232 and 530, both DB-25), it was possible to remove so much crap from the 232 that this did fit (ok, with giant omissions but still).