Mylex SCSI Controller, 16550A UARTS

Cliff C Heyer cliffhanger at
Mon Oct 2 09:25:57 AEST 1989

Karl Denninger Writes...
>In article <22542 at> cliffhanger at (Cliff C Heyer) writes:
>>Hopefully the Mylex will give 386 land the
>>*first* board that gives 900KB/sec disk I/O
>>like the Amiga (at Amiga prices hopefully)
>That's funny...
>The WD1007/WA2 has been clocked here at 950KB/second (ESDI 10 Mhz).  I
>understand that the WD1008 (15Mhz ESDI) has been clocked at over
>1300KB/second, although I haven't seen that one myself.  The DPT boards 
>have been clocked at that rate (950KB/sec) on cache misses.  On cache
>hits the DPT board is off the top of scale on our tests; that is in 
>excess of 4MB/sec!

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!  
This was confirmed by checking BYTE benchmarks that list 1MB throughput times.
SUN was the only machine in BYTE that showed a respectable 800KB/sec time.

It has become evident to me that in spite of 15MHz ESDI chips, sync SCSI, etc.
certain machines still go as slow as their ST-506 counterparts. Also, unlike
the old mainframe days when computer were rated in actual disk I/O in KB/sec, 
todays micros are sold with NO ratings, except the "chip throughput" ratings
which are meaningless because they do not show what the actual throughput

So I have no way to know if the machine I want to buy has 900KB/sec I/O, 
except from USENET. The sales people won't tell you anything. It seems that
disk I/O is a big secret, all they want you to think about is MIPS. You are
provided with NO information with which to make an informed configuration
decision. As soon as you do some disk benchmarks you have to sign a non
disclosure agreement. As a result, I have developed a somewhat cynical view that 
these companies have a vested interest to saturate the market with slow I/O
hardware, knowing that you will grow and later have to buy more hardware
to get the 900KB/sec. Why sell you a better mousetrap if people are happy buying 
the old one?

I'm hoping that if I am wrong, someone will be able to give me a convincing
argument otherwise.

Cliffhanger at

PS did any of you "shop" for 900KB/sec? If so, how did you establish this
speed actually was possible before you bought?

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