vac122g@monu6.cc.monash.edu.au (Daniel Bowen) (03/12/91)
Okay now, back to my age-old problem.
The disc drive on my prehistoric BBC B has bitten the dust.. so, I
need a new one. But it has to, of course, be the same format as the
old one so I can read my zillions of discs!
- Acorn Disc Filing System 1.2, Single density, 80 tracks based on
a very ancient 8271 disc controller.
- 80 track drive, double sided, running on single density.
Now, the clincher is this. Can I use a standard IBM-PC 1.2Mb drive? (Which
will be a great deal cheaper than having to order a special drive from
the UK, as Beeb distributors here are as rare as hen's teeth)
My logic says yes. A 1.2Mb drive is a double-sided, 80 track
drive running under quadruple density; am I right?
Where as I want a double-sided 80 track drive running under single
density; okay? But, the density is dependent on the disc controller,
is it not? That way on a PC a 1.2 can impersonate a 360... (which
would be a 40 track double sided, double density). But as I still
want 80 tracks, I should have none of those problems about disc
head width or whatever.
Anyway, one of these days I'll get round to borrowing someone's
drive and try it... but in the mean-time, have I figured it out
right?
Daniel Bowen
(Starving 8-bit Beeb owner!)
--
Raymond Luxury-Yacht a.k.a. DANIEL BOWEN | Remember - jumpers are
Monash University, Melbourne, Australia |----\ clothing's way of telling
vac122g@vx24.cc.monash.edu.au <-Both down from \ you to pull over...
vac122g@monu6.cc.monash.edu.au <-16 to 18 March \ [Toxic Custard Workshop]csuaw@warwick.ac.uk (Patrick Clark) (03/14/91)
Daniel Bowen writes: >Now, the clincher is this. Can I use a standard IBM-PC 1.2Mb drive? (Which >will be a great deal cheaper than having to order a special drive from >the UK, as Beeb distributors here are as rare as hen's teeth) > >My logic says yes. A 1.2Mb drive is a double-sided, 80 track >drive running under quadruple density; am I right? > >Where as I want a double-sided 80 track drive running under single >density; okay? But, the density is dependent on the disc controller, >is it not? That way on a PC a 1.2 can impersonate a 360... (which >would be a 40 track double sided, double density). But as I still >want 80 tracks, I should have none of those problems about disc >head width or whatever. Yes this seems to make sense to me . I have a PC disk drive on my beeb BUT it is only 40 trks .. somebody else fitted it for me. Hasving thought about it .. it must have been a 360k drive .. but I dont see any reason why you couldnt do the same with a 1.2 Mb drive. -- ______________________________________________________________________________ Patrick Clark | | 'In Europe and America University of Warwick | patrick@uk.ac.warwick.cs | theres a growing feeling Coventry , CV4 7AL | csuaw@uk.ac.warwick.cu | of hysteria. ' - Sting
gilbertd@p4.cs.man.ac.uk (Dave Gilbert) (03/15/91)
I thought 1.2Mb drives had a different type of magnetic head - something to do with needing a different amount of magnatisation for the different media (at least thats the story I heard why the 1.2Mb discs aren't SUPPOSED to work on other drives) -- ------------------------------------------------------------------------------- - Dave Gilbert - gilbertd@p4.cs.man.ac.uk - The MTBF of a piece of equipment - - G7FHJ@GB7NWP - is inversly proportional to its - ------------------------------------------- importance -
cabr07@vaxa.strath.ac.uk (03/15/91)
In article <1991Mar12.024637.12084@monu6.cc.monash.edu.au>, vac122g@monu6.cc.monash.edu.au (Daniel Bowen) writes: > The disc drive on my prehistoric BBC B has bitten the dust.. so, I > need a new one. But it has to, of course, be the same format as the > old one so I can read my zillions of discs! > > - Acorn Disc Filing System 1.2, Single density, 80 tracks based on > a very ancient 8271 disc controller. > - 80 track drive, double sided, running on single density. > > Now, the clincher is this. Can I use a standard IBM-PC 1.2Mb drive? (Which > will be a great deal cheaper than having to order a special drive from > the UK, as Beeb distributors here are as rare as hen's teeth) > > My logic says yes. A 1.2Mb drive is a double-sided, 80 track > drive running under quadruple density; am I right? Yes but an 8271 can handle only single density drives. > Where as I want a double-sided 80 track drive running under single > density; okay? But, the density is dependent on the disc controller, > is it not? That way on a PC a 1.2 can impersonate a 360... (which > would be a 40 track double sided, double density). But as I still > want 80 tracks, I should have none of those problems about disc > head width or whatever. An 8271 will handle a 720k IBM type drive with the right connector BUT you need a newer type of controller if you want to attach a quad density (1.2M) drive. > Daniel Bowen Gordon. -- -------------------------------------------------------------------------------- |G.N.Sinclair | JANET: G.N.Sinclair@uk.ac.strath.vaxa | |Physics & Applied Phys Dept| BITNET: G.N.Sinclair%vaxa.strath.ac.uk@UKACRL | |Strathclyde University | UUCP: G.N.Sinclair%vaxa.strath.ac.uk@ukc.uucp | |107 Rottenrow |Internet:G.N.Sinclair%vaxa.strath.ac.uk@nsfnet-relay.ac.uk| |Glasgow G4 0NG, Scotland | | --------------------------------------------------------------------------------
rogersh%t5e@uk.ac.man.cs (Huw J. Rogers) (03/16/91)
In article <gilbertd.669031425@p4.cs.man.ac.uk> gilbertd@p4.cs.man.ac.uk (Dave Gilbert) writes: >I thought 1.2Mb drives had a different type of magnetic head - something to do >with needing a different amount of magnatisation for the different media > >(at least thats the story I heard why the 1.2Mb discs aren't SUPPOSED to work >on other drives) There are three separate issues in disk formatting: 1) The track/sector layout (no. sectors/track, sector numbering, etc.) 2) The magnetic density (single, double, or quad) 3) The number of heads (sides) used (1 or 2) BBC DFS is 40/80 track, single density (FM encoding), 1 sided. BBC ADFS is 80 track, double density (MFM encoding), 2 sided. PC 1.44Mb (1.2Mb formatted) is 80 track, quad density (MFM2 encoding), 2 sided. Drives can step to either 40 or 80 tracks in the 5.25'' world, and can be single or double sided. All 3.5'' drives step to 80 tracks, but apart from this 3.5'' and 5.25'' drives are identical and can have as many configurations as each other. The density affects the amount of data you can store per track: FM - 2.5k; MFM - 5k; MFM2 - 10k. This data is split up into sectors (of either 128, 256, 512 or 1024 byte length) on the track. Drives are limited at the h/ware level as to what they can read by the following possibilities: 1) drive is limited to 40 track step resolution. 2) drive has only one head. 3) drive's FDC (Floppy Disk Controller) is FM only. 4) drive's FDC is FM/MFM only. The FDC is mounted internally in the computer and communicates the FM/MFM/MFM2 signal direct to the drive via the interface cable. BBC drives were so ubiquitous and supplied by so many different manufacturers that they fell into some or all of the above limitations. However none of them could read MFM2. The 8271 FDC was FM only, the later WD1770 was FM/MFM. The Archimedes 3.5'' drive also has this latter limitation - it cannot read MFM2 because it's FDC is a VL1772 (which is a WD1772 clone which is essentially a faster stepping variant of the BBC's WD1770.) The actual magnetic head is not, as far as I am aware, an issue here. STs and PCs also use the WD177x FDC standard as do IBM minis/mainframes, DEC vaxes (inc. MicroVaxes), Suns, and almost every other computer/embedded system manufacturer: Hence the ability to read each others disks given the right software/FDC combination. Sorry about this lecture, but the subject needed some airing judging from recent discussion... ;-) -Huw [ H.J.Rogers (INTERNET: rogersh%p4%cs.man.ac.uk@cunyvm.cuny.edu) ] [ ,_, (BITNET/EARN: rogersh%p4%cs.man.ac.uk@UKACRL.BITNET) ] [ :-(_)-o (UUCP: ...!uunet!cunyvm.cuny.edu!cs.man.ac.uk!p4!rogersh) ] [ _} {_ (JANET: rogersh%p4@uk.ac.man.cs) ]
mathew@mantis.co.uk (mathew) (03/18/91)
gilbertd@p4.cs.man.ac.uk (Dave Gilbert) writes: > I thought 1.2Mb drives had a different type of magnetic head - something to d > with needing a different amount of magnatisation for the different media > > (at least thats the story I heard why the 1.2Mb discs aren't SUPPOSED to work > on other drives) Get a 1.2MB disk. Hold it up to the light and look at the surface. Note the colour. Get a 360K disk. Hold it up to the light and look at the surface. Note the colour. They are different. It's not a rumour or a supposition. You can do the same with 3.5" 720K/1.44MB disks. mathew -- "These kinds of remarks are wholly inappropriate and are the mark of a bigot." -- Theodore A. Kaldis <kaldis@remus.rutgers.edu>