ISA bus throughput

[Tony Duell]

>  It's no news that cd-roms could operate in older
> machines. I remember a friend with a Tandy 1000
> something years ago who had one hooked up (can't
> remember if it was internal or external though). And
> he could listen to music while he was doing
> *presumably* something useful with the machine.

Most older CD-ROM drives had built-in DACs and thus an audio output. You 
could use that to play a music CD without using any of the host 
computer's CPU cycles at all (the external Philips I have has 
play/stop/skip track controls on the front, it can be used as a simple 
audio CD player without connecting it to a computer).

There was often an audio connector that you linked to your soundcard, 
but that just fed into the mixer stage of the soundcard. Again no host 
CPU cyclers were needed.

>  It would be nice to obtain a schematic of one of the
> more primitive IDE cards *whistles*. And wouldn't

I did trace out the schematics of the one in this machine. To be honest, 
it was totally trivial. A few buffers and a PAL. I would thoink you could 
design one by reading the IDE spec/

> artwork be nice too ;). Would an 8-bit card take the
> place of a 16-bit card in an AT? Presumably yes,
> albeit slower I guess. The Acculogic sIDE/16 or

Most IDE drives expect a 16 bit data bus, at least for the data register. 
The 16 data lines from the drive are buffered and fed to the 16 data 
lines on the ISA slot. 

-tony