followup

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Mar 30 00:02:58 1999

><I have no idea, however, how you block and deblock I/O with 1K blocks when
><you have only 1k in your sector buffer. I suppose I could go back and loo
>
>You copy the sector to the 1k ram area and then copy out the desired
>sector. the real trick is keeping track of whats in ram and if it has
>to be written back.


I guess it's fortunate there was only one DMA process going on at the time,
else it might have been real sticky figuring out what had been overwritten
already.. If you were doing a read in order to do a write, using DMA, you
might actually get tangled up. Fortunately that showed up while the vendor
was debugging his code, so I didn't have to deal with that.

><at the software, but the stuff I had at my disposal at the time seemed to
><work best with a big hard disk requiring the largest available granules
><(allocation blocks) and since the logical drives were limited to 8MB and
>
>the largest allocation blocks are due to the need to store in ram on a bit
>per allocation block basis, a bit for every allocation block on the disk.
>for something like a 8mb disk using 4k blcks that would be 256 bytes!


That's quite so. Fortunately one wasn't required to load data at the
granule size, but rather at the sector size, so you could get by with a read
of a 1K sector. Of course you had to read it before you could write it, so
you had to wait for the next revolution of the disk. All this went by so
fast, and, since I didn't run big databases requiring sorts to and from
disk, I didn't perceive much delay, as it only takes a few revolutions to
load up a program. So each drive had six logical drives on it.

><since CP/M was pretty much a thing of the past, I didn't see any point in
><wasting time and resources fine-tuning it. I used it because I had a few
><already-paid for cross assemblers and other tools for CP/M. Once a decent
><version of the PC-DOS became available, I was sure to make the switch. O
><course I didn't realize how long that would be. Nonetheless, once I had a
><PC with a '186 processor, I could run the CPM emulator to use my tools and
><the more modern hardware to do my work, and the CPM became a relic.
>
>Shame. I still use it. And I'm still finding ways to tune it for even
>more performance. It was the active full time OS amd machine until
>89 when I went pdp-11. After that it was the part time on line system.
>
>Current project is to add heirarchal directories (not the ZCPR user thing).
>it turns out to be doable though the bdos will have to be altered.


This all sounds like it could be fun if, for example, you're running it all
on classic and unmodified hardware. I'm not sure I'd want to try to earn my
living that way, though.

>Allison
>
Received on Tue Mar 30 1999 - 00:02:58 BST