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From: smvorkoetter@watmum.UUCP (Stefan M. Vorkoetter)
Newsgroups: comp.sys.ibm.pc,comp.sys.tandy
Subject: Re: Why no single density?
Message-ID: <673@watmum.UUCP>
Date: Tue, 18-Nov-86 09:05:11 EST
Article-I.D.: watmum.673
Posted: Tue Nov 18 09:05:11 1986
Date-Received: Tue, 18-Nov-86 22:04:46 EST
References: <437@moncol.UUCP> <1293@hoptoad.uucp>
Reply-To: smvorkoetter@watmum.UUCP (Stefan M. Vorkoetter)
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 11
Keywords: Intel 8272a, FDC, IBM-PC, Tandy 1000
Xref: mnetor comp.sys.ibm.pc:140 comp.sys.tandy:8

In article <1293@hoptoad.uucp> farren@hoptoad.UUCP (Mike Farren) writes:
>Single density disk controllers write the data to the diskette at 250K bit/
>sec.  Double density controllers do so at 500K.  The IBM controller has only
>the 500K clock on board - it would take a hardware change to allow it to
>do 250K. Not impossible, just impossible with the standard controller.

There is more of a difference between single and double density than that.
Double density is basically single density with some redundant flux transitions
left out to allow more data to be recorded without increased media bandwidth.
To record 250Kbps at single density requires just as high a clock rate as to
record 500Kbps at double density.