poking around inside an IBM PS/2 Model 80 from 1987, i noticed something odd going on with the expansion card connector. there are 8 extra pins in this connector, but why? the reason is really strange, and totally nuts!🧵
but first--this bus connector is NOT a PCI connector, it is Micro Channel! in the picture, PCI is on the top and Micro Channel is on the bottom.
coming off of the success of the ISA bus used in the IBM PC, XT, and AT, engineers at IBM decided to "do it right" this time around.
ooh, an Opticon infrared receiver. these are installed at traffic lights. emergency vehicles have a special transmitter that causes the light to change, giving them priority.
just thinking about these DIP-8 packages that have been converted to surface mount by trimming the leads short and bending them outwards. this is an official IC package! it's called DIP-8 gull wing.
oh look it's a working IBM 5154 enhanced color display, and it's on the auction site.
these monitors can handle 15.7KHz for the 200 line modes as well as 21.8KHz for 350 line modes. the polarity of the vertical sync signal tells the monitor which of the two modes to be in. that's about it.
there are better monitors out there, for sure. i like the original NEC Multisync because it can handle lots of different frequencies and standards, analog and digital.