Path: utzoo!utgpu!watmath!clyde!bellcore!rutgers!mailrus!caen.engin.umich.edu!sol.engin.umich.edu!billkatt
From: billkatt@sol.engin.umich.edu (Steve Bollinger)
Newsgroups: comp.sys.mac
Subject: Re: Mac Plus ??
Message-ID: <402a896e.a590@mag.engin.umich.edu>
Date: 10 Dec 88 06:30:00 GMT
References: <508NETOPRRW@NCSUVM> <771@husc6.harvard.edu> <401920b8.1285f@maize.engin.umich.edu> <1282@mace.cc.purdue.edu> <401a38a0.129dc@blue.engin.umich.edu> <1136@paris.ics.uci.edu>
Sender: netnews@caen.engin.umich.edu
Reply-To: billkatt@caen.engin.umich.edu (Steve Bollinger)
Organization: Computer Aided Engineering Network (CAEN), University of Michigan
Lines: 35
Sender:
Followup-To:

In article <1136@paris.ics.uci.edu> Andrew Kwan <kwan@io.ics.uci.edu> writes:

>>I can back my speed claims.  But first, I was unaware the Mac Plus supported
>>blind reads (in a very poor way).  The SE has a 2:1 interleave, the Plus, a
>>3:1, there is a 50% speedup already (2 turns per track as opposed to 3 turns
>>per track).
>
>Interleave refers to how many sectors (on the track) must be skipped
>over by the read/write head between sector accesses.  The difference
>in access time between the SE and Plus is a function of the disk's
>rotation speed and the number of sectors per track.  It is not
>dependent on the number of turns it has to make - sector accesses do
>not require having to wait until the track makes a full turn to get to
>the next sector to be accessed, only for the next one or two sectors
>to pass (to get to the one you want).

That is true to a point, but if you want to read the data on an entire track,
as you often do when loading a large program or file, interleave makes a big
difference.  On a 1:1 Interleave drive, you can read the whole track in one
revolution.  On a 2:1 Interleave, you can read every other sector on the first
rotation, and have to let them spin by again (another rotation) to get the
other sectors you skipped the last time.  On a 3:1 interleave, it takes 3
rotations for the same reason.  This is why a 1:1 interleave is 3 times faster
than a 3:1 interleave in many cases.

+----------------------+----------------------------------------------------+
| Steve Bollinger      | Internet: billkatt@caen.engin.umich.edu            |
| 4297 Sulgrave Dr.    +------+---------------------------------------------+
| Swartz Creek, Mi. 48473     | "My employer doesn't take my opinion any    |
+-----------------------------+  more seriously than you do."               |
| "You remember the IIe, it   +---------------------------------------------+
| was the machine Apple made before they decided people didn't need         |
| machines with big screens, color, or slots."                              |
|                                 - Harry Anderson (from NBC's Night Court) |
+---------------------------------------------------------------------------+