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From: tony@mwuk.UUCP (Tony Mountifield)
Newsgroups: comp.os.os9,comp.sys.m6809
Subject: Re: adding as disk drive to COCO3
Message-ID: <260@mwuk.UUCP>
Date: 22 Jan 91 09:44:59 GMT
References: <523@ctycal.UUCP> <1991Jan21.180211.11345@mentorg.com>
Organization: Microware Systems (UK) Ltd., Winchester, UK.
Lines: 37

In article <1991Jan21.180211.11345@mentorg.com> dclemans@mentorg.com (Dave Clemans @ APD x1292) writes:
> 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
[.............]
> 
> 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.

In actual fact, what Terry said is correct. To clarify:

At double density, both 3.5" and 5.25" drives run at 300rpm and are
clocked at 250kHz. This gives the standard 720k storage.

At high density, both types of drive are clocked at 500kHz. The 3.5"
drive still rotates at 300rpm, so this gives exactly double the
capacity, i.e. 1.44M. However, 5.25" drives in high density *ARE*
rotated faster, at 360rpm. This is why they only give 1.2M instead of
1.44M - the rotation period is shorter.

Both types of drive are normally switched between the two modes by a
signal on pin 2. This switches timings in the electronics, and in the
case of 5.25" drives also changes the motor speed. It is necessary for
the disk controller to match its clock rate with the pin 2 setting.

Tony.
-- 
Tony Mountifield.                | Microware Systems (UK) Ltd.
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