[sebhc] diskette drive

[melamy at earthlink.net]

a point of clarification, the National PC87322 supports 250kbs
which is single density. The original 765A if I recall correctly
did not have a data separator built in. The super I/O chips did
and they handle 250kbs (SD), 500kbs (DD) and then 1meg and 2meg
for high density formats.

The density can be set both by external jumpers as well as in
software.

On the issue of being clever, an elegant solution is one that
meets cost, time to market, or a combination of both. 
As for the Heath engineers being clever, sure. I didn't think
the Heath H8/H89 had DMA. That feature is a pretty hardware intensive
function and Heath was a very cost concious company. I suspect
that the engineers were told to make something work without DMA
- as I have always said "necessity is a mother."

For the record, I am an old fogey to and I certainly do not throw
chips at a design just to make it work. I will, however, use
state of the art chips to accomplish what I need to do. A few
months ago I used a $3 CPLD from xilinx to replace six cmos chips
that were taking up too much board space, costing just as much,
and giving me less functionality - now that is clever.

best regards, Steve Thatcher

>the PC. For instance, they left out single-density mode, which
is the
>standard format for all Heath distribution disks.
>
>Their apparent simplicity hides the fact that the
>designers were extremely clever, and made excellent choices
on how to do
>things. For instance, they got disk controllers to work *without*
DMA,
>on a very slow CPU.
>
>I know, this makes me an old fogey. The modern design philosophy
is "who
>cares how much hardware it takes -- chips are cheap. Just throw
enough
>of them at the problem. Who cares how much software it takes
-- memory
>is cheap. Throw in a few more megabytes. If it's too slow, raise
the
>clock speed -- who cares how much power it takes."
>



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