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Why no single density? [message #281242] Mon, 10 November 1986 23:56 Go to next message
john is currently offline  john
Messages: 294
Registered: February 2013
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Senior Member
Article-I.D.: moncol.437
Posted: Mon Nov 10 23:56:07 1986
Date-Received: Sat, 15-Nov-86 05:08:28 EST
Organization: Monmouth College, W. Long Branch, NJ
Lines: 26
Keywords: Intel 8272a, FDC, IBM-PC, Tandy 1000
Xref: watmath comp.sys.ibm.pc:79 comp.sys.tandy:4

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.).
 
Forgive a naive question, but why is this the case? Is there some
limitation of the disk controller in an IBM-PC which prevents single
density operation or is it some limitation of the BIOS?
 
Looking in the tech manual for my own machine (a Tandy 1000), I noticed
that it uses an Intel 8272A as the floppy disk controller. According to the
spec sheet, this chip is capable of single density operation. If so, then
why can't I find a program to use it that way?
 
Thanks in advance for any replies. If you know of a program which will deal
with single density disk, feel free to pass the name along.

-- 
Name:		John Ruschmeyer
US Mail:	Monmouth College, W. Long Branch, NJ 07764
Phone:		(201) 571-3557
UUCP:		...!vax135!petsd!moncol!john	...!princeton!moncol!john
						   ...!pesnta!moncol!john

	This isn't a coronation- this is bad comedy.
						-Galvatron
Re: Why no single density? [message #281243 is a reply to message #281242] Sat, 15 November 1986 07:07 Go to previous messageGo to next message
farren is currently offline  farren
Messages: 36
Registered: November 1985
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Member
Article-I.D.: hoptoad.1293
Posted: Sat Nov 15 07:07:02 1986
Date-Received: Sat, 15-Nov-86 23:54:55 EST
References: <437@moncol.UUCP>
Reply-To: farren@hoptoad.UUCP (Mike Farren)
Distribution: net
Organization: Nebula Consultants in San Francisco
Lines: 27
Keywords: Intel 8272a, FDC, IBM-PC, Tandy 1000
Xref: mnetor comp.sys.ibm.pc:87 comp.sys.tandy:5

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.).
 >  
 > Forgive a naive question, but why is this the case? Is there some
 > limitation of the disk controller in an IBM-PC which prevents single
 > density operation or is it some limitation of the BIOS?
 >  
 > Looking in the tech manual for my own machine (a Tandy 1000), I noticed
 > that it uses an Intel 8272A as the floppy disk controller. According to the
 > spec sheet, this chip is capable of single density operation. If so, then
 > why can't I find a program to use it that way?
 >  
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.



-- 
----------------
                 "... if the church put in half the time on covetousness
Mike Farren      that it does on lust, this would be a better world ..."
hoptoad!farren       Garrison Keillor, "Lake Wobegon Days"
Re: Why no single density? [message #281244 is a reply to message #281242] Mon, 17 November 1986 18:34 Go to previous messageGo to next message
Anonymous
Karma:
Originally posted by: henkp@nikhefk.uucp (Henk Peek)
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
Re: Why no single density? [message #281246 is a reply to message #281242] Tue, 18 November 1986 09:05 Go to previous message
Anonymous
Karma:
Originally posted by: smvorkoetter@watmum.UUCP (Stefan M. Vorkoetter)
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.
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