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5150 full height drives - 320k or 360k?

erikarn

Experienced Member
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Dec 14, 2020
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Oakland, California
hi!

My 5150 has two full height 5.25" drives, but my attempts at making 360k boot disks (yes, on a DD 5.25" drive in my 5170 - I remember that from the 90s!) has failed.

Are the drives 320k (8 sector) ? Is it just a BIOS/controller thing? If I make a 320k boot disk on the DD 5170 drive, is that expected to work?

Thanks!


-adrian
 
Yes. The difference is the version of DOS, not the drive (other than being double sided vs single sided). 1.0 was single sided, 8 sectors per track, 160K. DOS 1.1 added double sided support, so 320K. DOS 2.0 added formatting for 9 sectors per track, so 180K singles sided and 360K double sided.

As long as the drive is double sided, it will work as 320K or 360K. Same drives.
 
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DOS 2.x upgraded to 9 sector tracks from the 8 sector tracks of DOS 1.x. The 5150 controller and drive should work fine with DOS 2 or later disks. There are several potential problems and I am not sure which one you are having.

What DOS are you trying to place on the disk?
Early IBM 5150 drives are single sided and will not recognize double sided formats. 160/180 K formats only. Try using format with the /1 switch to make a single sided disk just in case you have single sided drives. It should boot in a double sided drive.
One drive may be out of alignment. Try swapping the A and B drives on the 5150. Remember to switch the terminator as well.
You might want to try to place the 5170 DSDD drive in the 5150. No drive will have better alignment with a drive than the drive itself. Supporting a half height drive in the full height bays is an interesting challenge but there are 3D printed mounting brackets for that.
 
hi!

So right now I'm just trying to whack DOS 6.22 on it, as I don't have a DOS 3.x image running on anything. That may change soon; I have sufficient 286-386 hardware now to setup other random DOS installations with these floppy drives.

How can I identify what kind of full height drive it is?

Also, will the 5150 BIOS boot a 9 sector boot disk, single sided OK?

And yeah, I know it could also be drive alignment and other drive woes; I just wanted to eliminate any user errors here first!

Thanks!
 
The Tandon single sided drives are TM100-1. There should be an IBM label with a part number on each drive. If you can't find the drive model number, it is possible to look up the IBM part number to figure out what drive it is.
https://ibm-pc.webnode.sk/en/collection/floppy-disk-drives/ has pictures of common models of floppy drives used by IBM. If your drives look radically different, it may be necessary to post pictures of the drive.

5150 BIOS has no problem with booting 9 sector single sided disks.
 
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The 8 sector thing on early DOS came from the datasheet for the µPD765 FDC. It was overly generous with the gaps, probably on the assumption that an open-loop DC-powered belt-drive spindle motor was going to be a problem along with the 1 msec "blind spot" after the index. In fact, it's perfectly possible to put 10 sectors per track to make a 400KB disk ever since the use of the second revision of the 765, µPD765A which cut that time by half.
 
ok, it looks like they're a variant of the Magnetic Peripherals Inc full height drive. I'll post some photos later. The PCB is a little different, but the part number is the same.

* It looks like someone swapped the drives but didn't swap the terminator, so I switched it - no dice
* I yanked out the drives and yeah, A: has a very stiff head sled, and B: is less stiff. I cleaned up the B: drive and re-lubricated it with some lithium grease - it now reads fine enough to boot MS-DOS 6.22 (minus a keyboard, so I can't finish booting it :)

It looks like I'm going to have to field strip this full height drive and give it a good cleaning and check-up to make sure the head stepper/sled is working OK.

thanks everyone! onto repair time!


-adrian
 
hi!

So the termination resistors for these Magnetic Peripherals 5.25" drives - it's a 14 pin DIP device with the part number 914C151X2PE. Does anyone know what the internal wiring is? it looks like it isn't a straight 7 x 150 ohm resistors inside.

Thanks!
 
It should be. The MPI drives use 7x 150ohm and the tandon drives use 8x 150ohm. I’ve got some extras of the MPI style if you need one. They can also be found at places like mouser.
 
update - it looks like it's 13 x 150 ohm resistors, with the common on pin 14.

Which is important, it means the orientation of the terminator on the magnetic peripherals drive matters. Brb, going to figure out what it SHOULD be on these drives..
 
Heh, I measured it out - it's 150 ohm from every pin to pin 14, and it's 300 ohms between pins except pin 14. So, that tells me it's a common tie point.

Ok, so that's done and now I know orientation matters! Next up!

The drive spindle is scratching against the bottom of the disk drive frame. If I pull the drive /out/ then the drive spindle is fine, and one of the drives boots fine. However, if I put it back in the case then it scratches against the bottom of the frame and obviously things stop working.

It doesn't have much clearance at all! Like, maybe a half millimeter or something sus like that? Does that sound right?

If I gently tilt the drive up a bit in the frame then everything works A-OK, but that's not exactly the best solution. The drives only mount using two screws on one side. I can get some paper or something to shove in the right places to keep the drive spindle above the metal case, but .. surely it wasn't always this bad? Has anyone seen this?

(The other doesn't; I'll crack out the scope and go check the drive speed, head alignment and signal levels. But the head moves fine, so at least i know the stepper isn't stuck anymore.)
 
Yup! I just went "hey there are two possibilities and I bet they're tied to 5" and bam! It's very obvious on the PCB once I knew what I was looking for.

Thanks!
 
It looks like there are two different PCB for these drives, even though the drives have the same model number. One has the terminator socket oriented 90 degrees from the other. The one I measured initially has 7 x 150ohm. I checked the other and it's just like what you describe. On the 7x150 style, there are 7 pins on the socket tied to +5


63A9AA83-1594-4F02-BEFB-4224F99AAFC8.jpeg

3270FC41-4F48-4FCB-9F84-553D2D4C8475.jpeg
 
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As long as the drive is double sided, it will work as 320K or 360K. Same drives.

Just to clarify: any FDD that's double sided will support 360k with the right version of DOS? Reason I ask is I have a Compaq (Siemens) FDD that I also suspect was originally rated for 320K. It's still in the original packaging, so I've never cabled it up.

Specs: Siemens/WST FD211-5 DS 48tpi
IMG_2652.JPGIMG_2653.JPG

Using DOS 2.0 or higher it should function at 360K just fine?
 
Using DOS 2.0 or higher it should function at 360K just fine?

I’d think so. I’ve got a compaq portable that from I think August of 1983 according to date stamps on the inside of the plastic case, and it supports 360K just fine. I haven’t removed the floppy drives, so I cannot be sure they are the same as yours, bust based on what Chuck posted earlier, I’ll bet it’s a safe bet.

Speaking of NIB stuff, I’ve got an IBM drive new in the box (a very nasty box) and it’s advertised as a 320K drive.

AA30E0D6-2F92-403A-97C0-32BEE557E04A.jpeg
 
I've seen a number of old PC and clone advertisements that described double sided double density 5.25" drives as "320k drives". Then the moment DOS 2.0 came out they all magically became "360k" drives. Unless you have an early Intel FDC chip, a dynamic disk formatter can even squeeze out around 420k. Mathematically, DSDD 40 track drives can store 500k bytes of raw data, but some has to be wasted for gap and used for headers and such.
 
There was such a thing as single density and single sided
Never saw one in an IBM 5150 though

As to your formatting issue you need matched DD disk drives in both computers

If one machine has a 1.2hd drive you can’t read data from said drive even on 360kb media
 
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