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View Full Version : modifying a 1.2 MB 5-1/4" drive to write osborne disks?



Mike Chambers
September 30th, 2006, 03:03 PM
as the title asks, can i modify my (only) working 1.2 MB 5-1/4" drive (or use software) to write osborne 1 disk images that will work in my first-gen osborne machine?? any info would be appreciated! i have image files for it already. i'd love to get some use out of that thing.

EDIT: damn, i'm sorry i didnt mean to post it in this subforum! oops.

modem7
September 30th, 2006, 03:25 PM
To get boot disks for my Osborne 1 (second version), I:

1. Went to http://www.classiccmp.org/dunfield/img/index.htm (quoted elsewhere in these forums).
2. Downloaded "Osborne 1 Single Density system disks"
3. Used ImageDisk to extract images to 2S2D diskettes in a 360K drive.

Mike Chambers
September 30th, 2006, 03:31 PM
To get boot disks for my Osborne 1 (second version), I:

1. Went to http://www.classiccmp.org/dunfield/img/index.htm (quoted elsewhere in these forums).
2. Downloaded "Osborne 1 Single Density system disks"
3. Used ImageDisk to extract images to 2S2D diskettes in a 360K drive.

dang... so i need a 360 KB drive? don't have any of those around.

isn't it possible to modify a 1.2 MB drive to act exactly like a 360 KB? i thought i've read about that before. then i would just tell the BIOS to treat it like a 360 KB drive after the modification...?

or am i wrong?

Mike Chambers
September 30th, 2006, 03:35 PM
hmmm after doing some research on google, apparently if i have a TOTALLY clean 1.2 MB disk (no present magnetic data) i can tell the BIOS my 1.2 MB drive is a 360 KB drive and i can write to it and older drives with fatter read/write heads should be able to pick it up because there is no other data to confuse it. i might try completely erasing one of my disks with a low level format and see what happens.

(i'm not expecting much..... but we'll see)

nige the hippy
October 1st, 2006, 02:56 AM
Erase it with a head demagnetiser (or equivalent) & you might stand a chance.

It's all about track width, head width, and the actual problem - eraser head width, the erase head of an 80 track drive erases a stripe half the width of a 40 track head, leaving un-erased stripes between tracks in 40 track mode. if you have a look around this forum there are quite a few discussions about what works with what.

I have some nice new 40T drives in the UK for a fiver each (to cover my time & packing) plus post, to people who I deem worthy of their discounted purchase!

chuckcmagee
October 1st, 2006, 06:16 AM
Yesss indeed, I did own a "Radio Shack cassette tape eraser". I would have to use that on many floppies that would give me "can't format" errors. I would turn on the monster, do a few circles close to the floppy, and Voila, it would format perfect after that. The eraser got very warm fast so you couldn't do many at one time, had to let it sit and cool off. Now, I just toss the disk rather than bother. Of course, can't do that with valuable OLD floppies.

Mike Chambers
October 1st, 2006, 11:54 AM
Erase it with a head demagnetiser (or equivalent) & you might stand a chance.

It's all about track width, head width, and the actual problem - eraser head width, the erase head of an 80 track drive erases a stripe half the width of a 40 track head, leaving un-erased stripes between tracks in 40 track mode. if you have a look around this forum there are quite a few discussions about what works with what.

I have some nice new 40T drives in the UK for a fiver each (to cover my time & packing) plus post, to people who I deem worthy of their discounted purchase!

thanks for the offer! i might do it. i dont have any demagnetizers... i was going to get on my 386 and write a little app to set all bytes on the disc to zero in 720 KB mode on this SD disk i have (to try to help clean up ALL the stripes)

then i'll switch the BIOS to think its a 360 KB disk and try running that ImageDisk program to write the osborne images and pray that it works.

mbbrutman
October 1st, 2006, 01:33 PM
As has been pointed out, the 1.2MB drives can read and write DSDD media. Just make sure it was virgin media. The head width thing has been discussed on this forum many times before.

Here is a more subtle problem. The 1.2MB drives are 80 track drives. To write correctly such that a 40 track drive has a chance of reading the diskette, you need to 'double step' the tracks. Otherwise, you are only reading and writing from the first 40 tracks, which is half of the surface area that you need to read a diskette written on a true 40 track drive.

The BIOS of the machine doesn't do anything like that. Hopefully ImageDisk does, and if it doesn't you might be able to get an enhancement out of the author. My gut feeling would be to just get a 40 track DSDD drive - they are not that rare.

Terry Yager
October 1st, 2006, 02:04 PM
As has been pointed out, the 1.2MB drives can read and write DSDD media. Just make sure it was virgin media. The head width thing has been discussed on this forum many times before.

Here is a more subtle problem. The 1.2MB drives are 80 track drives. To write correctly such that a 40 track drive has a chance of reading the diskette, you need to 'double step' the tracks. Otherwise, you are only reading and writing from the first 40 tracks, which is half of the surface area that you need to read a diskette written on a true 40 track drive.

The BIOS of the machine doesn't do anything like that. Hopefully ImageDisk does, and if it doesn't you might be able to get an enhancement out of the author. My gut feeling would be to just get a 40 track DSDD drive - they are not that rare.

Glad you mentioned that, Mike, becauze ImageDisk is able to write 40-track images, but not in the default instalation. It must be selected from a menu, as single-step (80-track) is the default installation mode. (As a new user, it took me awhile to figger that out, as it ain't very intuitive (there's that word again)). I didn't 'get it' at all until after reading thru several 'help' files (which are (surprizingly) actually helpful). Best to RTFM if attempting to use unfamilliar software.

--T

modem7
October 1st, 2006, 07:03 PM
Yes, ImageDisk supports double stepping, and yes, you do have to change the default value (ImageDisk won't let you use the default value when de-imaging).
And so expanded directions are:

1. Download the "Osborne 1 Single Density system disks" ZIP file from http://www.classiccmp.org/dunfield/img/index.htm

2. Download ImageDisk version 1.12 from the same site.

3. Find a computer with DOS and a 360KB diskette drive (i.e. 40 track, double sided). Needs to be 'true' DOS, not a DOS box within Windows. I used a 386-40 machine.

4. Insert the 2S2D target floppy (new or used) into A: (assumption - A: is the 360KB drive).

5. Run ImageDisk version 1.12

6. At the first screen, press ESC.

7. Change the double-step setting to OFF as follows:
a) Press S.
b) Arrow down to the double-step setting.
c) Press space bar until the double-step setting is shown as 'off'.
d) Press ESC.

9. Press W.

10. select the source file.

11. Press ENTER


NOTE 1: Leaving the Cylinders setting at 80 is not a problem - ImageDisk will use what is specified in the image file (40).
NOTE 2: Because the images used are single sided, a 160KB diskette drive (i.e. 40 track, single sided) can be used.
NOTE 3: If using a 1.2MB drive as discussed in earlier posts (something that I'd never do), the double-step setting would be set to 'on'.