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MFM 5.25 floppy with 5ali61

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First post, by Joakim

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Hey

I saw a 5.25 floppy drive and felt an urge to have it. It is a 1015-VI-F from micropolis from ca 1979. It seems like it was kind of premium for its time being dual headed and able to write a whopping 1 mbyte of data to a single floppy disk.

I realize it is ancient in comparison to my 1998 setup. Is it possible to use it, if I get myself an ISA MFM controller or do I need to complement my purchase with more fitting system? (I am almost hoping for a yes.)

Reply 1 of 49, by evasive

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Found a maintenance manual
https://www.abc80.net/archive/luxor/diskdrive … ance-manual.pdf
https://deramp.com/downloads/floppy_drives/mi … 16%20Manual.pdf

unsure if that can tell if it's compatible with the Shugart or the IBM PC interface
https://en.wikipedia.org/wiki/Shugart_bus

https://web.archive.org/web/20180630190124/ht … ents/floppy.pdf

Reply 3 of 49, by snufkin

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Wow, back when manuals meant something. Doesn't look like either PC or Shugart, what with DS4 on pin 34 (page 30 on the .pdf from deramp). Can probably be adapted though, most of the other signals are in the right place.

So I think what would need to be done is:
Connect PC pin 34 to Drive pin 6 (connects the ready signals)
Leave PC pins 4&6 not connected (so the drive isn't signalling ready on a reserved pin)
PC Pin 2 (Density Select) should be ok to connect to Drive pin 2 (HeadLoad) as the drive will perform the head load when the DS is asserted. Having a separate HeadLoad signal is apparently only there to make it possible to keep the heads in place to save time if swapping between drives. I'm assuming (haven't read all of the manual) that open the drive catch will make everything safe.

Sector/Index pulse diagrams worried me for a moment as it showed pulses per sector rather than revolution, then I remembered about hard sectored disks. So I think it should be ok for soft sectored disks. Set it as DS2 (same as Shugart DS1/PC Drive Sel B), then it should work as expected with a standard PC floppy cable. Not sure what controllers will make of a drive designed for 8 sectors/side, but I think pretty much all floppy controllers are MFM (FM might have been 8"?).

So it might work. Probably. I think.

[It's got a belt driving the main spindle! It's got strobe patterns on the main spindle for calibrating the spindle speed! And the manual has schematics! This is great.]
[Last thing before I get too far in to the manual, it looks like it might have a weird tpi (100tpi) so disks written on this drive are probably only readable on similar models. There's a bit here https://www.retrotechnology.com/herbs_stuff/d … ive.html#100tpi ]

[Last edit... So I got wondering about the exact model, since the manual wasn't quite lining up with the description in the ebay listing, and it looks like Micropolis had very similar model numbers for different drives. Found a link via Wikipedia to here https://books.google.co.uk/books?id=aj4EAAAAM … epage&q&f=false, which includes a snippet about Micropolis releasing some new 96tpi / 70 tracks/side drives, including the "1015-VI: a two headed version of the MFM drive, 872KB, priced at $530". So it looks like it is actually 96tpi, but only 70 tracks. Head may travel a bit further than that, so it's possible it'd get 80 tracks in. 70 tracks is sufficiently obscure that I can't just find anything about it. Things might still work (it is MFM, so that's standard floppy coding), but I'm a bit less confident that it'll just work]

Last edited by snufkin on 2021-05-17, 17:40. Edited 1 time in total.

Reply 4 of 49, by Joakim

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Yeah those manuals are awsome. Sadly only a 12 paged manual is included in the purchase, but it is in its original box.

Oh and I thought mfm was something else than the inbuilt controllers. Maybe I am mixing it up with mfm hard disk drives?

Should I be ok with one of those regular slot floppy cables and somehow move the wires to different pins? (I don't have a cable.)

What a out storage media? I read somewhere that you should have quadra density dual disks for these drives, but I never heard of them.

Edit I now read the article you linked snufkin and see there are some info on this. Thanks!

Reply 5 of 49, by snufkin

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Joakim wrote on 2021-05-17, 17:32:

Oh and I thought mfm was something else than the inbuilt controllers. Maybe I am mixing it up with mfm hard disk drives?

So my understanding is that early floppy drives were FM coded, so one transition in a given window for a '0' and two for a '1'. The regular transitions made it easy to keep the receiving end in sync in case you had a long sequence of '0's. Then they changed to Modified FM, with a single transition in the middle for a '1', and no transition for a '0', unless the previous bit was a '0', in which case there would be a transition at the start of the window. More complicated, but each bit now only needed the space needed for one magnetic transition rather than two, so the bits/inch could be doubled. And there floppies stayed through to 2.88MB. The floppy controller has to figure out the data rate by trial and error by looking at the RDATA stream coming from the floppy, trying to sync a PLL to it, then trying to read some header information from track 0, complete with some deliberately malformed bits that the controller can use as markers.

Anyway, point being that the standard PC floppy controller has to handle MFM.

So, SD was FM coding, DD is MFM coding, and I think QD is going from 48tpi to 96tpi, HD is then going from 9 sectors to 18 sectors/side.

My guess is that with any floppy controller then the drive will be able to write/read 9 sector/80 track disks (so a sort of 720k 5.25"). Although the drive heads might not be able to move far enough for the last 10 tracks. I don't know whether you'll need a specific controller to handle 8 sector disks. If it does work then the formatted capacity will likely be around 560kB (512 bytes/sector * 8 sectors/track * 70 tracks/side * 2 sides).

Should I be ok with one of those regular slot floppy cables and somehow move the wires to different pins? (I don't have a cable.)

You can probably bodge something together to test by taking a regular floppy cable, then use a knife to cut along the cable to extract the individual strands you need, then cut, strip, lengthen and rejoin as needed (e.g. extract wire 6 and 34, cut them, strip the ends of 6 from the drive and 34 from the PC, then link them together with a joining wire). You might get away with just twisting the wires together as a test since none of these are particularly sensitive Data signals.

What a out storage media? I read somewhere that you should have quadra density dual disks for these drives, but I never heard of them.

Don't really know, other than that link, which seemed inconclusive.

Essentially, I started out thinking it'd be a simple case of rewire the cable, then realised there were some format oddities. I think it'll probably still work, but with possible odd behaviour. OTOH, and this is the main reason I keep floppy drives in my computer, the sound when booting should be great.

Reply 6 of 49, by Deunan

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The 1015F MOD VI is QD drive - not very useful with PCs. All the cons and none of the pros. It's a nice drive, not doubt, I like these old things myself, but it's just not for PCs.

It is 96tpi so has narrow head and can do 80 tracks, but that means not being able to properly erase/write to typical DD 360k floppies. That BTW is a problem with any non-48tpi drive, not just this one in particular. But it has 300rpm motor, not 360rpm like the PC HD drives do. So you can just forget about 1.2MB floppies and frankly also 360k ones because there is no way to properly set i up in BIOS. If you set 360k you won't get double-stepping. If you set 1.2M then BIOS (so also DOS) will use 300kbit instead of native 250kbit data rate, that's how the 360->300 rpm problem is solved on PCs. But this one is already 300rpm...

With a proper cable/interface it might be a good drive for IMD to dump QD floppies - if you are into preservation and actually have QD 5.25" floppies. Otherwise I'd say it's not worth the trouble, unless you just like repairing old junk like I do 😀

Reply 7 of 49, by snufkin

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Deunan wrote on 2021-05-17, 18:44:

The 1015F MOD VI is QD drive - not very useful with PCs. All the cons and none of the pros. It's a nice drive, not doubt, I like these old things myself, but it's just not for PCs.

It is 96tpi so has narrow head and can do 80 tracks, but that means not being able to properly erase/write to typical DD 360k floppies. That BTW is a problem with any non-48tpi drive, not just this one in particular. But it has 300rpm motor, not 360rpm like the PC HD drives do. So you can just forget about 1.2MB floppies and frankly also 360k ones because there is no way to properly set i up in BIOS. If you set 360k you won't get double-stepping. If you set 1.2M then BIOS (so also DOS) will use 300kbit instead of native 250kbit data rate, that's how the 360->300 rpm problem is solved on PCs. But this one is already 300rpm...

With a proper cable/interface it might be a good drive for IMD to dump QD floppies - if you are into preservation and actually have QD 5.25" floppies. Otherwise I'd say it's not worth the trouble, unless you just like repairing old junk like I do 😀

Interesting. What would you think would happen if you told the BIOS it was a 720k 3.5" DD (I figure that's the closest standard drive to this one)? 300rpm would then be ok for the controller to sync to. I don't know if there was any change in the actual density of magnetic transitions between 8 or 9 sectors/track, or if they just had longer gaps between sectors for the 8 sector format. If the transition rate is faster then maybe the write electronics would struggle to cope with the difference? Drive rpm might need to be calibrated a bit tighter.

(only just thought to check, looks like DOS standard format command allows for /8 to set 8 sectors/track, although maybe that also sets total tracks to 40 as well).

Reply 8 of 49, by Deunan

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720k setting should work, but the problem is with media. You need QD floppies to have realiable write to them and 5.25" QDs are rare.

It might just work with DD if these are good quality, but I'm not sure about longevity and error rates. And BTW all such flopies will have to be properly demagnetized if to be used in standard 360k drive. HD floppies on the other hand will also kinda work but the write currents on QD heads are just barely strong enough to erase or magnetize HD media. It's not going to be reliable at all, especially after a few writes. Wikipedia lists QD floppies as 300 Oe but I seem to recall a different, higher number. If these are really just 300, like standard DD, then you can forget about the head being able to properly erase or write to 600 Oe media.

8/9 sector formats only differ in timing (gaps) between sectors and the last sector to index mark. On signal level it's not really a big issue, it looks like Amiga used 11 sectors and that worked. Problem is DOS is not really respecting the format byte on the floppy, instead it uses hard-coded values for specific floppy drive types reported by BIOS. So you are limited to these if you want to actually read/write files and not just access the floppy low-level via IMD or OmniDisk.

EDIT: Well, there's FDFORMAT package, sure, but that's not really standard and most "weird" formats require TSR loaded to patch the DOS code.

Reply 10 of 49, by Joakim

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I see. writing is the biggest problem due to heads being too weak and that's why you need QD media which is hard to find. This is maybe not a huge deal as long as I can find a few writable disks at least and I can have some fun.

What about reading? Would I be able to read 720 k disks? What about 360 k ones? What I really want to do is play for instance kings quest 1 from floppy.

Reply 11 of 49, by Deunan

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Once set to 720k the drive should be able to format, write and read back from floppies it made, assuming you use DD media. Again, if there are problems with writing over previous 360k content then a demagnetizing will surely help. There aren't any PC 720k 5.25" disks, at least none I know of - so it's usable as storage but not really for anything else.

Now, such drive should, in theory, be able to read standard DD 360k disks. But as I've said DOS will probably consider this a 3.5" drive and I'm not sure it will work or not. But FDREAD TSR should help here, it's exactly the use case.

If you can copy the contents of two 360k floppies to one 720k without filename collision then it should work (with FDREAD, which BTW also allows writing, don't let the name fool you).

Reply 12 of 49, by Joakim

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So I picked up the drive and it looks to be in almost mint condition except for some bent pins.

I still don't have a way of connecting this beast. I don't even dare doing so until I've read the manual thoroughly. Oh and I will scan the manual that came with it and post it here even though there seem to be some other manuals online.

There were some questions of Shugart or IBM and one of the pages it actually sais that some connectors are Shugart compatible. (I did not read that in manuals I found online.)

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Reply 13 of 49, by snufkin

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Joakim wrote on 2021-05-23, 17:26:

So I picked up the drive and it looks to be in almost mint condition except for some bent pins.

Lovely. Really like those curvy, organic traces (I guess hand drawn) around the Micropolis logo.

There were some questions of Shugart or IBM and one of the pages it actually sais that some connectors are Shugart compatible. (I did not read that in manuals I found online.)

I think the manual for a different version of the drive had the pinout as being neither Shugart or IBM (closest to Shugart I think), so it'll be interesting to see what this one is. Can't see any jumpers for configuring it, so fingers crossed you can make it work with just a modified floppy cable and not have to touch the drive at all.

Reply 14 of 49, by Joakim

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There is one jumper, which is not explained in my version of the manual but in an other version.

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It just sets the drive to no 1-4. (You can daisy chain these with up to 3 more drives.)

Now if I only could get ahold of a 44 pin floppy slot cable..

Reply 15 of 49, by snufkin

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Joakim wrote on 2021-05-24, 04:12:

There is one jumper, which is not explained in my version of the manual but in an other version.

Ah! I saw that and assumed they'd figured out a way to save a chip and put in a wire mod rather than fit the chip. Should have realised that if it was just a wire mod then they wouldn't have fitted the socket. Drive 2 would be the PC setting.

Joakim wrote on 2021-05-24, 04:12:

Now if I only could get ahold of a 44 pin floppy slot cable..

I'm being dense, the picture shows a 34 position edge connector, isn't that a standard 5 1/4" slot connector?

Last edited by Stiletto on 2021-05-24, 21:03. Edited 1 time in total.

Reply 16 of 49, by Joakim

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Yes typo. 34 pin! "Standard" and I don't have one yet. I'm a little confused about if I need to modify the connector (which should be quite easy to do) because there are a couple of pins that are not according to to shugard standard, the ones without stars next to them in the manual. I actually don't know much about what signals are actually needed but I would guess that the ready signal needs to be properly connected.

Sorry for the bad quality, my scanner at home is misbehaving so they were taken with my phone.

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Reply 17 of 49, by snufkin

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Yeah, looks like the only that's a real issue for connecting to a PC is the Ready signal. Probably a few ways to connect it up, but I think one way is to cut wire 6 and 34 in the cable, then join wire 34 from the motherboard to wire 6 from the drive. That leaves drive input 34 DS4 not connected, but I don't think that'll be a problem (likely pulled high on the drive). Set the drive as DS2, then it should work with a standard PC floppy cable (A: at end of cable after the twist, B: before the twist).

Head Load input to the drive will be driven by Density Select output from the motherboard, which aren't the same function, but I don't expect it'll actually matter. From the manual, I think the Head Load input is only useful if you want to save a bit of time by having the heads in place before the drive is selected, and the drive will put them on the disk as required when the drive is selected (via the DS input) regardless of the Head Load input. This may all be irrelevant since the manual suggests that some models don't even have a Head Load solenoid and the heads contact the disk whenever the door is closed.

If you get a full floppy cable (so one connector for the motherboard, two connectors just before the twist and two after) then you could do the 6->34 mod after the twist and put this drive at the end of the cable as A: (still set as DS2 though), then still be able to attach another standard drive on the B: connector.

Reply 18 of 49, by Deunan

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Joakim wrote on 2021-05-24, 09:45:

Yes typo. 34 pin! "Standard" and I don't have one yet. I'm a little confused about if I need to modify the connector (which should be quite easy to do) because there are a couple of pins that are not according to to shugard standard, the ones without stars next to them in the manual. I actually don't know much about what signals are actually needed but I would guess that the ready signal needs to be properly connected.

First you need to determine what kind of motor drives the spindle. It can be a more modern DC type motor, which will respond to Motor On signal, or it can be the older AC type. Which BTW might need 115V or 230V AC input, so do check. You will not easily find a replacement motor. If it is AC one then it can also be 50 or 60 Hz, or it might allow both by having 2 pulleys and you just put the belt on the correct one.

Your drive has/needs Head Load signal. No PC controller that I know of has an output to control that signal, but you can tie it with Motor On. Do note, depending on how the head mechanism works, if your PC hangs with the drive spinning (thus head still loaded) you might need to cut power first to safely remove the floppy. Note, Head Load must not be connected to Density Select which is present on pin 2 of PC FDCs, so re-route that wire or change it on the drive (with jumpers if there are any, or you could cut traces but preferably do that on the cable side).

You can usually ignore pins 4 and 6, these are usually not connected PC-side, but do check. Or just cut those on the cable to be sure. Ready, present on pin 4 on your drive, should be relocated to pin 34. Now, pin 34 should have Disk Change but you don't have a signal like that at all, not sure if Ready will do instead. It seems to work for 360k drives (BIOS actually tends to ignore it completly) but might just not for a 720k drive. If you get everything connected, spinning, etc, but DOS always says the drive is not ready, might be that signal. I can be worked around but with additional electronics, not some simple wire swapping.
BTW it should be safe to connect pins 6 and 34 on your drive, since 34 is input, and so long the drive is not jumpered to address 4 (and should not be for PC, it needs to be 2) it will not matter. Oh and some drives count the Disk Select address from 0, and some from 1, keep that in mind.

Rest should bolt as-is assuming you use a cable with a twist, you use the end (after twist) connector and the drive is jumpered to respond to DS2 signal. Then there is only the problem of power input, especially the spindle motor, rest is most likely the usual +5 and +12V. Some drives might need 24V too though - all that should be in the manual.

Reply 19 of 49, by Joakim

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Interesting. I'm learning a lot from you guys and I am very grateful. Nice to see you agree with the ready signal being needed! 😀

I post the PDF that I managed to make last night but for some reason the pages are in the wrong order. Also some are missing but it is because they were simply were not in the package. Maybe they were full of (very bad) pictures and when they were printed 40 years ago someone probably wanted to save ink! 😀

I have tried to compare the manual to the one online and it does not look to be exactly the same but I really have not put too much effort into it. On sheet 18/19 it sais "All waveforms shown high true." and I guess it means they are "pulled up true"?

I am a little confused about the section about the power on page 11/19. I have a 4 pin Molex connector on my model, but I also have the 10 pin molex connectors. Is 4 pin molex is enough? Maybe the other connectors are there for compatibility reasons?

I will come back to you on the motors. 😀

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