See comments embedded below, plz.
----- Original Message -----
From: allisonp <allisonp_at_world.std.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, May 30, 2000 4:07 PM
Subject: Re: Defining Disk Image Dump Standard
> >I always figured the reason for the restriction was dumb boot PROMs,
which
> >only know how to do programmed I/O to the FDC, and 8" DD comes in too
fast
> >for typical 8-bit CPUs of the time to handle with PIO. If the boot PROM
on
> >a particular system is smart enough to set up DMA, no need to require SD.
>
>
> it's an artifact of how people though the DDmedia was speced by IBM and
> a lack of knowledge of CP/M boot as everyone just followed the book
blindly.
>
> Not all required {or even had it!} DMA to do DD, CCS didn't.
That's proof that DMA was unnecessary! A DMAC cost quite a bit back then.
> I'd add that DMA was mostly uncommon save for the more refined or robust
> systems.
>
> Allison
>
>
I don't see how adding an unnecessary part makes a system more robust or
refined. It was quite straightforward to write and run FDC handlers that
used programmed I/O quite adquately and since CP/M and other simple OS'
seldom did anything useful with the small segments of saved time, (12
u-sec's per byte) it didn't help. Some other devices might have justified
DMA, but floppy drives actually didn't unless they were used with an 8080 or
other slow processor.
>
Received on Tue May 30 2000 - 19:20:35 BST