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From: prw@meccsd.MECC.MN.ORG (Paul R. Wenker)
Newsgroups: comp.sys.apple
Subject: Re: Apple Drive bashing (Was: noKLICKstart in comp.sys.amiga)
Message-ID: <796@meccsd.MECC.MN.ORG>
Date: Fri, 11-Sep-87 11:13:04 EDT
Article-I.D.: meccsd.796
Posted: Fri Sep 11 11:13:04 1987
Date-Received: Sun, 13-Sep-87 02:12:30 EDT
References: <3905@well.UUCP> <341@remsit.UUCP>
Reply-To: prw@meccsd.UUCP (Paul R. Wenker)
Organization: Minn. Educ. Comp. Corp.
Lines: 26

In article <341@remsit.UUCP> rem@remsit.UUCP (Roger Murray) writes:
>In article <3905@well.UUCP>, ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes:
>> 	Apple pulled this stunt years ago.  "Lets save a few cents on the
>> drive," they said.  "Let's leave out the track 0 detect switch," they said.
>> "We'll just ram the head against the physical stop 39 times," they said.
>> "It can't possibly do any harm; just give the user indigestion."
>
>Being an Apple owner [Yes, I still have my ][+...], I've always wondered
>about that.  Why 39 times (or whatever it may be)?  Was there a scientific
>method used, or did the number just look good to somebody?

When an Apple boots up, the firmware has no way of knowing which
track the head is on.  What it does is assume that the head is
on track 80 and then seeks the head out to track 0.  This way, no
matter where the head is, it is pretty much assured to end up at track
0.

On an I/O Error, DOS 3.3 pulls the same trick.  If DOS can't find the
sector it's looking for, it assumes that it's on the wrong track.  It
then sets the current track to 39 (35 tracks + 4 for good luck), seeks
out to 0 to get it's bearings again, and then trys to find the sector
it was looking for.


-Paul R. Wenker
-MECC