Path: utzoo!utgpu!watmath!clyde!att!pacbell!lll-tis!oodis01!uplherc!esunix!blgardne
From: blgardne@esunix.UUCP (Blaine Gardner)
Newsgroups: comp.sys.amiga.tech
Subject: 2090A speed
Keywords: I feel the need, the need for speed.
Message-ID: <1106@esunix.UUCP>
Date: 23 Nov 88 15:26:11 GMT
Organization: Evans & Sutherland Computer Corporation
Lines: 45

I've got one of the first A2090A controllers with a Seagate ST4096
hooked up to the ST506 interface. Diskperf consistantly returns maximum
read speeds of 200K to 220K. 

This seems awfully slow for a DMA controller, especially since a
couple of friends with the old, non-DMA, CLtd SCSI controller are
getting 300K to 350K. One has an ST506 (really, a 5M ST506) with a SCSI-
ST506 adapter, and the other has a 65M Seagate SCSI (I don't know the
model number).

Why would a DMA interface with a 28 mS drive be so much slower than a
non-DMA interface with 40 and 85 mS drives?

One possiblity is that I need to change the interleave from 1:1 to
another value. But I was under the impression that the 2090A could handle
data at full speed from the drive.

If I do need to change the interleave, is it possible to just reformat
one partition with a different interleave, or do I have to start from
scratch with Prep? If interleave is the problem, I'd like to make trying
different interleave values as painless as possible.

What about buffered seek? This is a feature of the ST4096, and I
understand that it's supposed to improve drive speed. Does the 2090A
support this feature?


On a slightly different subject, has anyone successfully formatted an
ST506 drive that has more than 8 heads? My ST4096 is a 9 head drive, but
I can only format with 8 heads, so I've got 9 meg going to waste. :-(
I got some e-mail from Dale Luck saying that if the 2090A didn't work
with more than 8 heads, a PROM swap would fix it. Dale offered to get
the PROM to me, but I've been unable to make e-mail contact with him.

Any help with getting the 9th head working would be greatly appreciated!


For the record, this is an A2000, 3M RAM, A2090A, ST4096, WB & KS 1.3.
The 2090A is in the slot nearest the CPU slot, and the 2M ASDG card is
in the second slot.
-- 
Blaine Gardner @ Evans & Sutherland    580 Arapeen Drive, SLC, Utah 84108
Here: utah-cs!esunix!blgardne   {ucbvax,allegra,decvax}!decwrl!esunix!blgardne
There: uunet!iconsys!caeco!pedro!worsel!blaine (under construction)
"Nobody will ever need more than 64K."    "Nobody needs multitasking on a PC."