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From: iverson@xstor.com (Tim Iverson)
Newsgroups: comp.periphs.scsi,comp.sys.ibm.pc.hardware
Subject: Re: How much faster is a 16 bit SCSI Card than the ST02?
Message-ID: <1991May30.191630.20435@xstor.com>
Date: 30 May 91 19:16:30 GMT
References: <396@oiscola.Columbia.NCR.COM>
Reply-To: iverson@xstor.com
Followup-To: comp.periphs.scsi
Organization: Storage Dimensions, Inc.
Lines: 51

In article <396@oiscola.Columbia.NCR.COM> dmoyer@oiscola.Columbia.NCR.COM (Dan Moyer) writes:
>I currently have a 386sx with a Seagate ST-02 and ST296N SCSI disk.
>With CORETEST and with Nortons SI benchmark, I get a reading of about
>220-300 K bytes/sec transfer time, and a 28-31 ms access time.
> 
>I currently operate DOS and sometimes Windows 3.0 now.   Sometime
>in the future (6-12 months), I'd like to be able to use OS/2 2.0 or
>Unix.  
> 
>1)  What performance increase can I expect with a adapter card
>    like the IN2000 or ADAPTEC 1542B, using the same ST296N disk.

Under Windows 3.0, you will notice a (perhaps significant) decrease in
transfer rate if you go to a bus-mastering controller due to the double
buffering used to work around the physical-to-virtual translation.

Also, under DOS, none of the standard benchmarks work with the Always
card.  That is to say, they return results that are much higher than
reality.  This is because Always disables all interrupts during BIOS disk
transfers (thus the clock doesn't tick and transfers take zero time :-).
This trick can cause serious problems with serial port i/o.

>5)  In planning to goto OS/2 2.0 or Unix in the future, what should
>    I avoid purchasing?

Avoid non-bus-mastering host adapters.  Overhead under a multi-threaded OS
is very high for these critters (Always is not bus-mastering, Adaptec 154x
and WD7000 are).

>Should I change my idea of getting a SCSI
>    adapter alltogether, and just get a faster IDE or ESDI drive, and
>    keep the old card?

SCSI is easier to integrate and (with some drivers) more reliable.  ESDI is
faster in a single disk or single threaded system, SCSI is faster in a
mult-disk and multi-threaded system.  If you're going with Unix, you can add
tape and CD-rom to the same host adapter that drives your disk.

With most SCSI disks, if you develop a defect in an awkward place, you can
reformat to "remove" it; formatting maps out defective blocks, presenting a
flawless image of the media.  Some drivers, like the ones we sell with our
products :-), are smart enough to remap defects on-the-fly, so you'll never
even see one until you run out of spares.  Reformat and you can gain a new
set of spares.  With ESDI, you're SOL.

>  Dan Moyer
>  dmoyer@oiscola.columbia.ncr.com


- Tim Iverson
  iverson@xstor.com -/- uunet!xstor!iverson