One mystery to me was why did the industry stick with the EIA-232 levels for terminals and whatnot long after differential EIA-422 was introduced. Higher-speed, better noise immunity, single-ended power supply... Seems that the popular places were Appletalk and ST506 data lines. But not on DTE/DCE. If you were using full-voltage (±15-±25) at high speeds (>500Kbps), the slew rates were ridiculous.
Inertia? My old 80286 motherboard had junper-selectable 232 or 422. Still have a couple of tubes of 422 drivers/receivers. --Chuck
