Date : Thu, 25 Jun 1987 1724:00
From : w_smith%wookie.DEC@decwrl.dec.com (Willie Smith, LTN Components Eng.)
Subject: re: hard/ram disk for S-100
JEllsworth@HI-MULTICS.ARPA was looking for a hard disk or RAM disk for an
S-100 machine. A few ideas, taken from my present configuration and my
current wish list:
1) Compupro (Viasyn) DISK-3 hard disk controller. This will talk to any mix of
ST-506 drives, does 24 bit DMA of any number of sectors, can work in track/
sector or absolute sector number mode, and has local intelligence (8085?) to
take care of all the messy details for you. You set up a 16 byte I/O Parameter
Block in memory and kick the DISK-3. It reads it into internal memory, does
the requested function (complete with seeks, head settles, etc), and gives you
back (in the IOPB) a completion status. Writing the software drivers in Z-80
assembly was very simple, and I have yet to have a problem with the board. I'm
running with 2 ST-225 drives, which seem to work well, in an Integrand
disk box,
which is very well built and (I suspect) bulletproof....
2) Macrotech 512K VRAM board. This is kind of expensive for a RAM disk,
but it provides real memory access _and_ RAM disk simultaneously. I'm using
part of the additional memory for BIOS extensions, I just load up my registers
with the important variables, swap banks, and have more than enough room to
play. It's nice having 64K free for your BIOS.... :+) The one thing that bugs
me about the VRAM is that while the memory section is real fast (they do some
handwaving to say it's 12 nS, but the chips are 120 nS), the RAM disk ports
need 2 I/O wait states with a 6 to 8 MHz Z-80.
Digital Research Computers LS-II(?). Not to be confused with the software
company of the same name, you can find them in the back of BYTE. The Light
Speed II is a 1 Meg version of their LS-I (256K), which I played with last
weekend and was very impressed with. These are really quite inexpensive,
and should work well if you are just looking for straight RAM disk, and can
handle a little kit assembly.
A little side note: with the DISK-3 and the VRAM board, you can
fairly easily whip up a hard disk cache. You get to the sectors that are
in the cache thru the RAM disk ports, and the DISK-3 does DMA to the memory
side. This does not work with the LS-II or other 'pure' RAM disks. Just
on the off chance that you end up with this configuration (or see below),
drop me a line and I'll see about sending you the drivers. In some simple
benchmarks of 'real world' applications, running a RAM disk made things go
4 times as fast, while the cache was 'only' twice as fast, but the cache
doesn't give 'DISK FULL' errors when it fills up....
3) Macrotech ADIT board with external RAM boards. The ADIT board can substitute
for the RAM disk ports on the VRAM board if you have memory in other banks that
you are not using. It will do DMA between banks, and also has virtual RAM
disk ports that will keep track of everything for you. You also get from 4 to
16 I/O ports and a 6 MHz Z80 and 16 or 32K of RAM and a little tiny multitasking
'operating system' in an EPROM that runs everything for you! I've ordered one
cuz I need some more serial ports, but I suspect I'll be adding a couple of
meg of memory boards for a RAM disk and rewriting my cache software to take
advantage of the ADIT instead of the VRAM. Wanna buy a VRAM board? :+)
Hope this helps, any questions, feel free to send mail.
Willie Smith
w_smith@wookie.dec.com
w_smith%wookie.dec.com@decwrl.dec.com