Mylex SCSI Controller, 16550A UARTS

Keith Ericson keithe at tekgvs.LABS.TEK.COM
Fri Oct 6 08:19:16 AEST 1989

In article <22709 at> cliffhanger at (Cliff C Heyer) writes:
>Michael Umansky Writes...
>>In my 25Mhz Micronics with 8Mhz AT bus and Adaptec AHA-1542A SCSI controller
>>and CDC WREN III SCSI drive I get about 900 KB/sec.  The Mylex controller
>>should deliver at least a magnitude more to be cost effective.
>Cliff Heyer Responds...
>I became interested in speed when I was asked to evaluate porting VAX applications
>to IBM PC/compatible micros. During my analysis & testing, I found the MIPS more
>than adequate in PC land, but disk I/O was the problem.
>The VAX ranges from 600KB/sec to 1.3MB/sec tops sustained I/O *per job*. Many
>PCs I tested got in the range of 200KB/sec (ST-506 ...). Then I found to my
>surprise that SCSI & ESDI disks on many machines was still 200-300KB/sec!  

Around here we use the CORE27 as our reference test; it seems to be
pretty accurate on the machines we can measure with other schemes
and we hope it extrapolates to the faster drives.

Anyway, using CORE27 to test an Everex STEP/25, a WD 7000ASC and a
CDC WREN IV (? 300 Mbytes) I got 1.04 Mbytes/sec.  That was some
time ago, however, and I've abandon that configuration.

I'm currently trying to get an Adaptec 1542A connected to a CDC WREN
VI (? 600 Megabyte) into my STEP/25.  But I have to wait for some
PAL upgrades for the STEP/25 because it doesn't "work and play well"
with the 1542A's bus-master DMA scheme...

In the meantime I've installed the 1542A and CDC drive into an Intel
301 to get the drive configured and my files loaded onto it while I
await the PALs.

Using CORE27 on the Intel 301, Adaptec 1542A and CDC combination I
get 1.4+ Megabytes per second reported.  When (if?) I get it working
in the STEP/25 I'll let you know how things go (the Intel 301 is a
16 MHZ processor and 8 MHz bus; the STEP/25 is set up for 8.33 MHZ
bus).  This is with no caching program loaded.


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