hdrw@ibmpcug.co.uk (Howard Winter) (04/09/91)
It was written as a joke, but actually it used to happen: Memory chips were made which had more cpaacity than was needed in the finished chip, and the different banks were tested. Depending on which banks had faults, the connection from the chip to the package was made, so that the good banks were being used, the bad ones weren't. Nowadays I don't think they do this. BTW I understand the medium used in DD vs HD disks IS different, and that the coercivity (the ease with which magnetism becomes permanent) is the variable. I have certainly never been able to reformat an HD 3.5" to 1.44 once it has been formatted at 720, and I believe that the switching of strength of magnetism used is the reason - the weaker HD field cannot overcome the 720. But I may be wrong... Howard. -- Automatic Disclaimer: The views expressed above are those of the author alone and may not represent the views of the IBM PC User Group. -- hdrw@ibmpcug.Co.UK Howard Winter 0W21' 51N43'
david@kessner.denver.co.us (David Kessner) (04/10/91)
In article <1991Apr9.075828.2135@ibmpcug.co.uk> hdrw@ibmpcug.co.uk (Howard Winter) writes: >BTW I understand the medium used in DD vs HD disks IS different, >and that the coercivity (the ease with which magnetism becomes >permanent) is the variable. I have certainly never been able to >reformat an HD 3.5" to 1.44 once it has been formatted at 720, >and I believe that the switching of strength of magnetism used >is the reason - the weaker HD field cannot overcome the 720. > >But I may be wrong... > >Howard. The HD disks are different from the DD disks... I dont know why this is really a question. I mean, just look at them! HD disks are darker and more highly "polished". DD disks are rather dull... I have always had a problem reformatting disks at a different density, I dont know why. Using a big magnet or a bulk eraser will fix the problem, however... I for one will never use disks beyond their rating (ie, using DD as HD, or SS as DS). While it may work for the most part, you do get more errors than normal-- perhapse only one critical error every 10-20 disks but you never know WHEN that error will pop up. I'd rather have some piece of mind, rather than play Russian Roulette... -- David Kessner - david@kessner.denver.co.us | do { 1135 Fairfax, Denver CO 80220 (303) 377-1801 (p.m.) | . . . If you cant flame MS-DOS, who can you flame? | } while( jones);
jpc@fct.unl.pt (Jose Pina Coelho) (04/11/91)
In article <1991Apr10.075541.638@kessner.denver.co.us> david@kessner.denver.co.us (David Kessner) writes: [......] I for one will never use disks beyond their rating (ie, using DD as HD, or SS as DS). While it may work for the most part, you do get more errors than normal-- perhapse only one critical error every 10-20 disks but you never know WHEN that error will pop up. I'd rather have some piece of mind, rather than play Russian Roulette... Why ? Do you have your mind backed up in a floppy ? -- Jose Pedro T. Pina Coelho | BITNET/Internet: jpc@fct.unl.pt Rua Jau N 1, 2 Dto | UUCP: ...!mcsun!unl!jpc 1300 Lisboa, PORTUGAL | Home phone: (+351) (1) 640767 - If all men were brothers, would you let one marry your sister ?
buckland@cheddar.ucs.ubc.ca (Tony Buckland) (04/12/91)
In article <JPC.91Apr11105328@terra.fct.unl.pt> jpc@fct.unl.pt (Jose Pina Coelho) writes: >In article <1991Apr10.075541.638@kessner.denver.co.us> >david@kessner.denver.co.us (David Kessner) writes: > ... I'd rather have some piece of mind, rather > than play Russian Roulette... Actually, you can get all the pieces of mind you want *by* playing Russian Roulette. All over the walls and the furniture.
bill@bilver.uucp (Bill Vermillion) (04/13/91)
In article <1991Apr10.075541.638@kessner.denver.co.us> david@kessner.denver.co.us (David Kessner) writes: >In article <1991Apr9.075828.2135@ibmpcug.co.uk> hdrw@ibmpcug.co.uk (Howard Winter) writes: >>BTW I understand the medium used in DD vs HD disks IS different, >>and that the coercivity (the ease with which magnetism becomes >>permanent) is the variable. I have certainly never been able to >>reformat an HD 3.5" to 1.44 once it has been formatted at 720, >>and I believe that the switching of strength of magnetism used >>is the reason - the weaker HD field cannot overcome the 720. The reason you can't reformat to 1.44 is that the system checks the density of the disk IF IT HAS BEEN PREVIOUSLY WRITTEN UPON. Bulk erase it and it will work just fine. The HD format current requirements will EASILY overwrite anything that DD writes. But you first have to let the machine know that the disk IS blank, and only a bulk eraser can do that. -- Bill Vermillion - UUCP: uunet!tarpit!bilver!bill : bill@bilver.UUCP
hdrw@ibmpcug.co.uk (Howard Winter) (04/17/91)
No - you CANNOT reliably use DD disks as HD - especially 5.25". You can certainly format them (there is no physical indication of the disk type, as there is with 3.5") but you will find that the Format program reports about 25% bad sectors. The inner tracks just cannot take the density unless they are made of the correct material - and 360K disks just aren't. Try writing on sandpaper (the rough side!) with a pencil - you'll find that it is possible with fine grades, but the coarser the grit, the less legible the writing. It's pretty much the same with magnetic media. Disks really aren't that expensive - losing data can be priceless! Howard. -- Automatic Disclaimer: The views expressed above are those of the author alone and may not represent the views of the IBM PC User Group. -- hdrw@ibmpcug.Co.UK Howard Winter 0W21' 51N43'
nigelm@ohm.york.ac.uk (Nigel Metheringham) (04/18/91)
In <1991Apr17.000314.29195@ibmpcug.co.uk> hdrw@ibmpcug.co.uk (Howard Winter) writes: >No - you CANNOT reliably use DD disks as HD - especially 5.25". >You can certainly format them (there is no physical indication >of the disk type, as there is with 3.5") but you will find that >the Format program reports about 25% bad sectors. The inner tracks >just cannot take the density unless they are made of the correct >material - and 360K disks just aren't. This applies just as much to 3.5 inch disks. We have just had a set of people demonstrating software at an exhibition here. One bloke had bought his precious programs with him (only one copy) on some 3.5 inch 720KB disks with the extra hole punched in them to persuade the PC that they were really 1.4MB disks (apparently his Lab had run out of disks in the few days before he came to the exhibition). Our systems could read about 75% of the disk, but wouldn't touch the inner tracks on any of the drives we tried. The morals (probably loose) of the story are:- 1. Use disks of the correct type for the capacity you want. 2. Always have a second copy. 3. If its important have an extra set of copies, or some other way of rebulding it. 4. If its very important don't let it near a computer in the first place :-) ! Nigel. -- # Nigel Metheringham # EMail: nigelm@ohm.york.ac.uk # # System Administrator # Phone: +44 904 432374 # # Department of Electronics # Fax: +44 904 432335 # # University of York, Heslington, York, UK, YO1 5DD #