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From: north@apple.UUCP (Donald N. North)
Newsgroups: net.micro.mac
Subject: Re: 800k drives faster?
Message-ID: <6980@apple.UUCP>
Date: Fri, 24-Jan-86 19:33:34 EST
Article-I.D.: apple.6980
Posted: Fri Jan 24 19:33:34 1986
Date-Received: Sun, 26-Jan-86 04:37:47 EST
References: <216@a.sei.cmu.edu>
Reply-To: north@apple.UUCP (Don North)
Organization: Apple Computer, Inc.
Lines: 25

In article <216@a.sei.cmu.edu> tgl@a.sei.cmu.edu.UUCP writes:
>Apparently the new 800k drives are supposed to be twice as fast
>as the old drives.  Does anybody know how Apple did this?
>
There are two reasons:

1) The 800k drives do their own speed control in their onboard micro.  For
the 400k drives, the 68k processor fills the infamous 'disk pwm' buffer with
the appropriate values (determined at boot time) to set the speed of the
disk (track dependent), then had to wait in a timing loop until it knew the
speed was correct.  This whole process took some time.

2) The 800k drives have a ready line to tell the 68k when they are ready to
transfer data.  In the 400k drive system, the 68k spends a lot of time in 
timing loops to determine when the drive will be ready to transfer data.

The media format is the same between the 400k and 800k drives (except the
800k's use both sides, of course).  Hope this answers your question.

Don North
Apple Computer, Inc.
Advanced Development Group

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