Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!think!ephraim
From: ephraim@think.COM (Ephraim Vishniac)
Newsgroups: comp.sys.mac
Subject: Re: Reekes on Disktimer (actually, MacWorld on DiskTimer)
Message-ID: <31230@think.UUCP>
Date: 13 Nov 88 03:04:14 GMT
References: <698@mouse.UUCP> <7595@well.UUCP> <20306@apple.Apple.COM> <7625@well.UUCP>
Sender: news@think.UUCP
Reply-To: ephraim@think.com (Ephraim Vishniac)
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 32

In article <7625@well.UUCP> brecher@well.UUCP (Steve Brecher) writes:
>> MacWeek has found that the timings of DiskTimer II have no 
>> correlation with real world performance.
>
>*No* correlation?  I missed the article referred to...

So did I, but:

The current issue of MacWorld (December 1988) has a review of umpteen
20-megabyte drives.  They measured performance in three ways:
DiskTimer II, their own "reality check" (a single 512Kbyte read), and
a series of end-user operations (copying files, launching
applications, opening documents).

From DiskTimer and the reality check, they calculated data transfer
rates.  I was very surprised at the level of agreement.  DiskTimer was
always marginally more optimistic, but the differences were slight.
(BTW, for a good laugh note that the graphs on page 134 are labelled
in "kilobits/second," with the fastest drive rated at about 2.5Kb/S.
Time for a sanity check on those captions...)

The important lesson comes in comparing the transfer rate graphs to
the "Real-World Performance" graph.  In data transfer rates, the
drives vary by a factor of 4:1.  But by "real-world performance," the
range is less than 2:1 and the rankings are different.  I've said it
before, but I'll say it again: data transfer rate is over-rated.

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?"