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Black 1.2MB Floppy Drive

I refer you to the IBM 5170 Technical Reference, page 9-5 "Diskette Drive Compatibility".

The IBM AT used Ye-Data drives that were noisy and, in my experience, generally unreliable. So, too, were the Qume drives used in the PCjr and Portable PC -- IBM even had to modify DOS in version 2.1 to slow down the disk timing to make the Qume drives work right!

And then there are also people who claim that you have to low-level format a stepper-motor MFM/RLL hard drive every six months, to account for seasonal temperature changes, or else you'll get read/write errors and data corruption. Meanwhile, the ST-225 in my 5150 hasn't been formatted since 1998, and it still works perfectly to this day...
 
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Originally Posted by Chuck(G)
I refer you to the IBM 5170 Technical Reference, page 9-5 "Diskette Drive Compatibility".

The IBM AT used Ye-Data drives that were noisy and, in my experience, generally unreliable. So, too, were the Qume drives used in the PCjr and Portable PC -- IBM even had to modify DOS in version 2.1 to slow down the disk timing to make the Qume drives work right!

And then there are also people who claim that you have to low-level format a stepper-motor MFM/RLL hard drive every six months, to account for seasonal temperature changes, or else you'll get read/write errors and data corruption. Meanwhile, the ST-225 in my 5150 hasn't been formatted since 1998, and it still works perfectly to this day...
A lot of that stuff is just for ‘CYA’ purposes. :)
 
I don't follow you. You're saying that it's okay with certain floppy drives and not others? Can you construct a matrix of drives and models to show what works?

My point was that simply saying that it is terrible practice. If you're going to make a 48 tpi disk, use a 48 tpi drive; if you're going to make a 96 tpi disk, use a 96 tpi drive.

I am aware of some of the Amiga people taking 96 tpi Teacs and doing an on-board jumper operation to get them to double-step to get an effective 48 tpi--some old MPI/CDC drives can do this as well. But why bother? Are 48 tpi drives that much of an endangered species?
 
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I don't follow you. You're saying that it's okay with certain floppy drives and not others? Can you construct a matrix of drives and models to show what works?

Yes. Half-height 360K drives have less trouble reading disks written to using 1.2MB drives than full-height drives. In fact, it's pretty much down to the margin of error; if one of my disks ever ended up being unreadable in a half-height 360K drive, chances are, either the disk had bad sectors, was contaminated with mold/fungus, was shedding oxide, or a previous bad disk gunked up the drive's heads, causing even good disks to become unreadable. Maybe I just have a lot of bad disks in my collection, but in my experience, a 360K disk becoming unreadable because it was previously written to using a 1.2MB drive is less likely the case than any of those other scenarios.
 
Yes. Half-height 360K drives have less trouble reading disks written to using 1.2MB drives than full-height drives. In fact, it's pretty much down to the margin of error; if one of my disks ever ended up being unreadable in a half-height 360K drive, chances are, either the disk had bad sectors, was contaminated with mold/fungus, was shedding oxide, or a previous bad disk gunked up the drive's heads, causing even good disks to become unreadable. Maybe I just have a lot of bad disks in my collection, but in my experience, a 360K disk becoming unreadable because it was previously written to using a 1.2MB drive is less likely the case than any of those other scenarios.
Based on many years of personal experience I'm going to agree with you 100% once again.
 
I was planning on setting up a 96TPI drive, and a 100TPI drive and experimenting with them by telling my PC they're "720K 3.5 drives" using the BIOS, and then see what happens. I am thinking I can possibly trick my computer to reading and writing that way. It will be interesting to see which works better this way, assuming the drives themselves are fully operational. I was able to format a bootable 8" disk by making the computer think it was a 1.2mb HD drive. Works "ok" not perfect.

Just for fun.

That said...I agree with Chuck and whomever else - you're better off using the drive as intended. Mixing and matching TPI is hit or miss and can be a waste of time..
 
The 100 tpi should behave like an ordinary 96 tpi drive (I've been using them since Micropolis introduced them way back when). However--they're only rated for 77 tracks (like an 8" drive) and you'll have to confine yourself to the 250-300 kbps data rate. Also note that most 100 tpi drives use the "Micropolis" pinout for drive select (slightly different for DS3 and READY). Use DD media.

If I recall correctly, the outermost track is also a bit further toward the edge of the disk, so that a 96 tpi drive will register the 100 tpi track 0 as somewhere around track 6. I don't think there was any substantial difference in the heads between the 96 and 100 tpi drives, just the track spacing and position.

If you're using the old Micropolis leadscrew-positioner drives, track-to-track timing is very slow--around 15 msec. The more modern Tandon TM-100/4M and MPI (don't remember the model) use taut-band positioners and are much faster. However, the Micropolis drives are very accurate and use something like 4 steps per track.

Hope this helps.
 
2.4 MB drives exist. see http://www.vintage-computer.com/vcforum/archive/index.php/t-13205.html Obscure and mostly used by the IBM 3174. One of the more forgotten backwaters of floppy technology.

I stand corrected :D - although it's not a PC format. From what I can tell, you could probably fool a PC controller into reading/writing the correct format, but what would be the point? There wouldn't be another PC on earth that could read it (unless you build 2:/)

Might be worth trying it on a controller that supports 2.88, but from the link above it appears that the data rate is 500kbps so that might confuse things?
 
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