Cursed Derp wrote on 2024-07-24, 20:56:

Is there an adapter to plug a 5.25 drive into a 3.5 slot?

I'm sure there are (but a dual connector cable would be easier)

I have several systems where I swap out different types of floppy drives - I made up a cable with a 37-pin 'D' connector at
the back of the PC so that I could more easily plug "most anything" in - It only has a 5.25" drive
connector and I use various adapters to accommodate other drives.

I recently posted a photo of the adapters in your "CAN I FIT IT IN MY PC" thread!

Dave Dunfield - https://dunfield.themindfactory.com

DaveDDS wrote on 2024-07-25, 03:26:

If you read the diskette back on the same (1.2M) drive - no problem, the thinner head doesn't see the "noise" at the
edges.

Not always. The HD head write is much stronger, the magnetic field it generates tends to "spill" outside its narrow head on DD media. It can even affect nearby tracks, sometimes after a time when some of the weaker magnetic domains flip to closest strong field nearby. In other words, a HD write on DD floppy has the potential to degrede with time, much faster than it would if the media was properly written.

Deunan wrote on 2024-07-25, 15:30:

DaveDDS wrote on 2024-07-25, 03:26:

If you read the diskette back on the same (1.2M) drive - no problem, the thinner head doesn't see the "noise" at the
edges.

Not always. The HD head write is much stronger, the magnetic field it generates tends to "spill" outside its narrow head on DD media. It can even affect nearby tracks, sometimes after a time when some of the weaker magnetic domains flip to closest strong field nearby. In other words, a HD write on DD floppy has the potential to degrede with time, much faster than it would if the media was properly written.

That certainly sounds plausible, but I will say that as the creator of "ImageDisk", I've worked *a lot* with floppy disks. and I've never
seen this happen, and I don't recall seeing any mention of it in any of the technical documents I consulted during my research into floppies...

That doesn't mean it's not possible, and to be fair, I'm relying on memories of research I conducted almost 20 years ago.
It kinda says something that IBM provided the capability - and again, I don't recall any mention of it in their documents.

Although personally, I always used actual 40-track DD drives when writing 360k media - and I even (probably still) have a
DD 80-track 5.25" drive (not HD) which I used when creating diskettes for some system that used that media format.

Dave

Granted, the track to track issue is rather rare - in theory the erase heads should be trimming the edges of the track but that too requires correct media to work properly. You can have 80 tracks on DD media (QD drives), though it's not reliable system if HD head / write current is used.

This is still mostly the bit to bit, or rather flux reversal, issue. It's also the very reason HD floppies use different coating material - less dense (to prevent these spills) and with higher coercivity (so it both resists weaker magnetic sources and provides better response for the head).

One way of making decent DD floppies on HD drives (not great, but should work well if the heads are properly aligned) is to fully erase the media first. Demagnetize or use GreaseWeazle hi-frequency write (preferably serveral passes per track in 80 track mode) to destroy any leftover data. On such a floppy a "spill" might even be beneficial, widening the track and makaing it easier for the DD head to pick it up. Such floppy shouldn't age any worse than if written with a DD drive, but to be sure somebody would have to write a buch of floppies and store them for 25+ years.

Deunan wrote on 2024-07-27, 09:46:

Granted, the track to track issue is rather rare - in theory the erase heads should be trimming the edges of the track but that too requires correct media to work properly. You can have 80 tracks on DD media (QD drives), though it's not reliable system if HD head / write current is used.

Which is exactly why I have an 80-track DD (QD) drive - to reliably write QD disks for those systems which used them.

One way of making decent DD floppies on HD drives (not great, but should work well if the heads are properly aligned) is to fully erase the media first. Demagnetize or use GreaseWeazle hi-frequency write (preferably serveral passes per track in 80 track mode) to destroy any leftover data. On such a floppy a "spill" might even be beneficial, widening the track and makaing it easier for the DD head to pick it up. Such floppy shouldn't age any worse than if written with a DD drive, but to be sure somebody would have to write a buch of floppies and store them for 25+ years.

I think I mentioned this in my previous post - I still have two bulk erasers in the drawer, for the rare cases when I did have to write
DD images on HD drives.

Dave

I don't know much about drive compatibility, all the ones I've had read disks just fine. But if you want a really robust and reliable drive, I would recommend the Alps branded drive used in the original 5170 AT. I'm not sure if this applies to all models, but at least the ones used by IBM had painted bezels which prevent them from yellowing.
I also really like the way these drives feel when engaging and disengaging the latch.

There is a "density select" pin on some 5.25" HD drives (pin 2 IIRC).

I seem to recall that some drives actually changed the write flux density, and others just
changed the rotation speed. I also have a vague memory of something in the IBM docs
discussing different densities available on the original AT 5.25"HD drive...

But this is all going back way to far to reliably recall, and unfortunately I don't have the
IBM AT docs anymore.

Dave

I think there are scans of the AT manuals available, including the service manual. I want to say it's on minuszerodegrees.

Wow I got the ImageDisk guy on here

Bro that's epic

Cursed Derp wrote on 2024-07-28, 12:15:

Wow I got the ImageDisk guy on here

Always glad to help out with retro system/storage problems (always been an area of interest to me).

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal