I've always been curious about this.
What makes the AT keyboard protocol superior to XT?
It supports command strings. Here is a wikipedia article:
It's bi-directional, so it allows the system to send commands to the keyboard, like setting typematic rate/flow control, or turning the leds for the 'lock' keys on/off.
Aha, that makes perfect sense. Thanks!
some keyboard during transition periode may also have a switch underneath to determine how its operate, on XT mode or AT mode,
such keyboard can be used for a both XT or AT type computer.
-fffuuu
Also interesting:
https://www.cs.cmu.edu/~jmcm/info/key2.txt
I had to smile at this point(s) where it says
[..]The keyboard itself also has a small buffer and there is hardware flow-control for preventing
overruns. All of this seems simple and quite elegant, but by the time we
get to the AT keyboard the details of the implementation are so complicated
as to ruin an otherwise ideal keyboard.
The XT keyboard's interface almost captures the above elegance (indeed it is
the only elegant thing about the XT, IMHO)[..]
[..]Once IBM found that it had a nearly perfect keyboard it, of course, decided
that it had to be almost completely redesigned for the AT. The keyboard
didn't have to be redesigned- there were enough extra scan-codes for the
AT's 101 key keyboard and the repeat mechanism could simply have been moved
to the BIOS. But no, they had to redesign everything. Sigh.[..]
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