Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!bloom-beacon!think!ephraim
From: ephraim@think.COM (ephraim vishniac)
Newsgroups: comp.sys.mac
Subject: Re: Jasmine Direct Drive 50 and a Plus
Message-ID: <18948@think.UUCP>
Date: 6 Apr 88 12:50:51 GMT
References: <23013@bbn.COM>
Sender: usenet@think.UUCP
Reply-To: ephraim@vidar.think.com.UUCP (ephraim vishniac)
Organization: Thinking Machines Corporation, Cambridge, MA
Lines: 32

In article <23013@bbn.COM> levin@BBN.COM (Joel B Levin) writes:
>I just got a Jasmine Direct Drive 50 for the office Plus...

>I found disktimer II and ran it.

>  Read   117
>  Write  126
>  Seek     0 (no seeking due to the large number of sectors per
>              cylinder, I believe).

I should have mentioned in my previous followup that this is not the
right explanation for the seek time.  It's true that disks with large
numbers of platters, hence many sectors per cylinder, give small
numbers for "seek" in DiskTimer II.  The numbers aren't that small,
however.

As I mentioned before, the Quantum drives have a large internal cache.
DiskTimer II *attempts* to measure seek time by repeatedly reading two
sectors a megabyte apart on the drive.  With a cache, the seek occurs
only once and then the sectors are repeatedly read from the cache.  In
order to avoid this effect, DiskTimer II would have to make large
reads between tests to flush the cache.

Beware of nonsensical test results!



Ephraim Vishniac					  ephraim@think.com
Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214

     On two occasions I have been asked, "Pray, Mr. Babbage, if you put
     into the machine wrong figures, will the right answers come out?"