john@moncol.UUCP (John Ruschmeyer) (11/11/86)
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
farren@hoptoad.uucp (Mike Farren) (11/15/86)
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"
henkp@nikhefk.uucp (Henk Peek) (11/18/86)
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
smvorkoetter@watmum.UUCP (Stefan M. Vorkoetter) (11/18/86)
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.