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From: henkp@nikhefk.uucp (Henk Peek)
Newsgroups: comp.sys.ibm.pc,comp.sys.tandy
Subject: Re: Why no single density?
Message-ID: <61@nikhefk.UUCP>
Date: Mon, 17-Nov-86 18:34:02 EST
Article-I.D.: nikhefk.61
Posted: Mon Nov 17 18:34:02 1986
Date-Received: Mon, 17-Nov-86 21:45:12 EST
References: <437@moncol.UUCP> <1293@hoptoad.uucp>
Reply-To: henkp@nikhefk.uucp (Henk Peek)
Distribution: net
Organization: NIKHEF-K, Amsterdam
Lines: 23
Xref: mnetor comp.sys.ibm.pc:121 comp.sys.tandy:6
Apparently-To: rnews@mcvax


In article <1293@hoptoad.uucp> farren@hoptoad.UUCP (Mike Farren) writes:
>In article <437@moncol.UUCP> john@moncol.UUCP (John Ruschmeyer) writes:
>>Recently I've been looking at ads for programs to read/write alien disks on
>>an IBM compatable. One thing I've noticed, though, is that none of them
>>support the formatting of single density disks (old Osborne I, TRS-80 Model
I, etc.).

>>Is there some imitation of the disk controller in an IBM-PC which
>>prevents single ensity operation or is it some limitation of the BIOS?

>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.

The olivetti M24 (ATT 6300) has a single- double density switchs-
circuit on the motherbord floppy controller. A bit in a floppy contol
register does the switch. I don't have documentation with me.
I think that this machine wil boot from single density floppys.
At boot the bios switch between both modes when it can not read your
boot floppy.

henk peek  henkp@nikhefk.uucp   seismo!mcvax!nikhefk!henkp.uucp