Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!psuvax1!husc6!m2c!wpi!dseah
From: dseah@wpi.wpi.edu (David I Seah)
Newsgroups: comp.sys.apple
Subject: Re: 5.25 floppy disk formats
Message-ID: <6818@wpi.wpi.edu>
Date: 16 Jan 90 20:03:52 GMT
References: <2403@ttardis.UUCP> <973@rbdc.UUCP>
Reply-To: dseah@wpi.wpi.edu (David I Seah)
Organization: Worcester Polytechnic Institute, Worcester ,MA
Lines: 35

In article <973@rbdc.UUCP> mitch@rbdc.UUCP (Mitch Berry) writes:
>Speaking of Disk drives...i was curious to a couple of things about apples
>3.5" disk drives.....
>
>1- why does the regular Mac 800k 3.5 has Two write protect switches, which
>   the HDFD (high desity floppy drive) has a second for detecting a HD disk.

High Density (HD) disks have just one write protect tab, which is in
the same place as it is on a regular 800K floppy.  The "extra" hole on
a high density 3.5" floppy is detected by high density drives.
Without the hole, the HDFD will just assume that the disk is a normal
double density floppy.

Apparently, in many brands of 3.5" disk there is little or no
difference in the actual magnetic media used in double and high
density disks.  There are tools that allow you to punch in the hole
without getting destructive plastic shrapnel inside the disk.  More
daring types can melt a hole into the disk with a soldering iron.
Boom!  Instant high density disk!  You should run some tests on the
born-again disk to make sure it can handle life in the fast lane.

>2- what IS the differnce between a 800k 3.5 and a HD 3.5 drive byt apple , 
>   just roms? drive head or a lot of the above??

I'm not too sure of the hardware particulars, but it involves
different drive electronics and finer heads to handle the increased
data density.  The stepper motor might be of a finer resolution, so
the heads can step to tracks that are much closer together.  I have a
sneaking suspicion that most 3.5" drive mechanisms today can
read/write high density, if the control hardware was designed for it.

These are guesses!  Guesses!  Guesses!
-- 
Dave Seah | O M N I D Y N E  S Y S T E M S - M |   Internet: dseah@wpi.wpi.edu 
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