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Use 3.5 drive as 5.25

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MikeS

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Is it possible to use a 3.5HD drive and pretend to MS-DOS or Windows that it is a 5.25DD drive, i.e. format and R/W a 3.5"DD disk with 40 tracks and 9 x 512 byte sectors ?

I've played with DRIVER.SYS and DRIVPARM but no success... ;-(

Thanks,

mike
 
Why would you want to do that way? (which isn't going to work)

Just use IMD for that. It allows you to write pretty much any geometry the FDC supports.
 
You are connecting a HD drive to a XT or equivalent? AFAIK the drivers see that it isn't a DD drive and won't work. With a DD drive those drivers should work.
 
Floppydrives are that stupid things that an XT can not see a difference between a DD and HD drive, and not differentiate between 3.5 and 5.25 inch. It will work, but some cases only as long as you read/write these disks only in that computer.

So if you connect a 80 tracks drive to an XT and does not tell that it is a 80 tracks drive, it will do single step and uses only the first 40 tracks of the disk, with the half width of gap between two tracks like a 40 tracks drive does. This is not compatible to a real 40 tracks drive. (When writing 40 tracks disks with a real 80 tracks drive, the computer must know to do "double step", some drives also have a jumper for double step which has to be set depending on the type of floppydisk you want to write, if the computer does not know about double step 40 tracks)

If you connect a HD drive to a computer that only supports DD, then only DD mode of the drive is used. 3.5 inch is a bit special, as these drives and HD disks have an extra hole to detect HD mode. So the HD drive with a HD disk internally switches to HD mode, but computer still writes in DD data rate. The result is a highly magnetified written track in SD/DD data rate (9 instead of 18 sectors). DD drives will not properly read that strong signal.

If you connect a 5.25 inch 80 tracks drive to a computer which has been setup for 3.5 inch drive, it will work, the computer will not see any difference. Maybe step rate is to slow for old 5.25 inch drives, so they may not move the tracks reliable. For some systems there are tools to set the steprate from 3 to 6 ms, so that is fixable (example: Atari ST).

If you connect a 40 tracks drive to a computer which is setup to 80 tracks drive, it will format up to 40 tracks correctly, but then clonk and failure on track 41.

If you connect a single sided floppy drive to a computer setup for double side, you still can write/format single sided disks with it, but double side will fail.

If you connect a double sided floppy drive to a computer configured for single side operation, you will not be able to access 2nd side of double sided diskettes.
 
MikeS said:
Is it possible to use a 3.5HD drive and pretend to MS-DOS or Windows that it is a 5.25DD drive, i.e. format and R/W a 3.5"DD disk with 40 tracks and 9 x 512 byte sectors ?

I've played with DRIVER.SYS and DRIVPARM but no success... ;-(

Thanks,

mike
Click to expand...
Yes and No.

You don't mention what computer you want to use to create and use these disc's on. For example:
On my IBM XT 5160 with the 11/08/82 bios and stock floppy controller and HD 3.5" floppy drive connected. If i use a 720k or 1.4M floppy (with density hole covered) the Bios will see them as 360k floppy's and attempt / format them as such.

With the later 86 dated Bios, The Bios will see them as 720k floppy's and attempt / format them as such.
I have in the past successfully used 720k and 1.4M floppy's formatted as 360k for use in my XT.

Using said floppy's in a different computer can often lead to failure / Corruption, YMMV.
For my IBM XT i have also used the [ Setdrive ] and [ Dskimage ] utilities, Read the txt files.
 
Just call the 3.5" drive a 360K 5.25' drive in you BIOS or configuration. Most of the time it will work fine so long as you use DD media--they're both 300 RPM and the big difference is in the number of tracks. You'll use only half the drive, but otherwise you should be fine. Floppies are very dumb things. You may run into issues with BIOSes on later (486+) systems where the BIOS does a seek test during POST, but if the BIOS has an option to disable that, you should be okay.
 
Thanks everyone for the replies.

On one end is a PC that only has an FPC 3.5" floppy, so no 5.25 interface or BIOS option; on the other end is an S-100 Cromemco system which has the ability to read & write MS-DOS format 5.25" floppies but no 3.5" DD or HD (unless emulating an 8" drive with a 360RPM modified drive.

Checking some more it looks like the Cromemco also doesn't like the 3.5" drive type; how on earth does it know? Same 300 RPM, same interface, unless it checks the number of tracks...

More research is called for, although it looks like I may have to put a small 5.25 tweener on my desk after all.
 
MikeS said:
Thanks everyone for the replies.

On one end is a PC that only has an FPC 3.5" floppy, so no 5.25 interface or BIOS option; on the other end is an S-100 Cromemco system which has the ability to read & write MS-DOS format 5.25" floppies but no 3.5" DD or HD (unless emulating an 8" drive with a 360RPM modified drive.

Checking some more it looks like the Cromemco also doesn't like the 3.5" drive type; how on earth does it know? Same 300 RPM, same interface, unless it checks the number of tracks...

More research is called for, although it looks like I may have to put a small 5.25 tweener on my desk after all.
Click to expand...
Does it do a seek test? That'd help tell it.
 
Two things: READY signal on pin 34. 360K drives generally have it, some DD 3.5" do but no 3.5" HD comes that way factory configured (although some allow you to jumper it).
And, of course, the number of tracks. However, if it were that, the Cromemco could not distinguish between a 96tpi DD drive (e.g. Teac FD-235F) and a 3.5" DD drive.
 
1ST1 said:
This is a very confusing thread now. Because now it is a "S-100 Cromeco system", but we are here at
area of the forum. There is also

which would mach much better.
Click to expand...
I'm not sure the source of the disk is important; the question is how to read a 360K 40 track 9 SPT MS-DOS format disk on a PC. It could just as well come from another PC.
 
Chuck(G) said:
Two things: READY signal on pin 34. 360K drives generally have it, some DD 3.5" do but no 3.5" HD comes that way factory configured (although some allow you to jumper it).
And, of course, the number of tracks. However, if it were that, the Cromemco could not distinguish between a 96tpi DD drive (e.g. Teac FD-235F) and a 3.5" DD drive.
Click to expand...
What do driver.sys and drivparm effectively do? I assumed that one or the other could be used to override whatever the BIOS assumed but apparently there's more to it...
 
Driveparm informs DOS what to attempt as the driver. However, if the parameters returned from the BIOS don't match with what the driver expects, you're out of luck. You can use an installable device driver to ignore what the BIOS says.
 
Chuck(G) said:
Driveparm informs DOS what to attempt as the driver. However, if the parameters returned from the BIOS don't match with what the driver expects, you're out of luck. You can use an installable device driver to ignore what the BIOS says.
Click to expand...
Thanks, Chuck; guess I'll have to set up a 5.25" system.
 
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