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From: dclemans@mentorg.com (Dave Clemans @ APD x1292)
Newsgroups: comp.os.os9,comp.sys.m6809
Subject: Re: adding as disk drive to COCO3
Message-ID: <1991Jan21.180211.11345@mentorg.com>
Date: 21 Jan 91 18:02:11 GMT
References: <523@ctycal.UUCP>
Organization: engr
Lines: 24

From article <523@ctycal.UUCP>, by ingoldsb@ctycal.UUCP (Terry Ingoldsby):
> The first problem is *easy*.  What you don't realize is that the 1.2 MByte
> floppy disk drives spin faster (350 RPM ??) than the standard 80 track
> drives (300 RPM).  Think about it.  You start to lay down the format on the
> disk.  Your CoCo thinks it knows how long it takes for the disk to spin
> so it writes out formatting info at that pace.  Unfortunately for you
> the disk revolves more quickly and you overwrite the beginning of the
> track.  Simple!
> 
> There is nothing you can do to fix the controller, you must slow down the
> drive.  Most 1.2 MByte disk drives use motors that have two speeds. 
> Sometimes there is a jumper, sometimes a wire that must be disconnected
> to select 300 RPM.  Do this and you will suddenly have a working drive.
> Your storage will only be about 700K, *not* 1.2 MByte.
> 

To clarify things, 1.2 Meg drives DO NOT!! spin faster than other drives.
The disk moves at EXACTLY the same speed.

The difference between them is in the electronics.  1.2 Meg drives are clocked
twice as fast as the slower drives.  Controllers that can handle both drives
have the ability to switch clock rates.

dgc