All you never wanted to know about 8 inch floppy drives
Hello! Today we are going to talk about floppies. Uh, not that floppy - it's not even floppy, so it doesn't count. But the actual real floppy thing. And so, that's the five and a quarter inch.
But that's the one for babies, we want to talk about the one for adults: the eight inch floppy. Three we go, it fits. So, that's how the floppy was born, this is the original format from IBM. Well, hello and welcome back. If you follow the channel, you know that we had a previous run-in with 8” floppy drives, when we helped paleontologists recover a trove of fossil data, locked into what turned out to be the very first IBM floppy format for IBM 360 mainframes.
And during that adventure, we also befriended the multi-talented Antoine, part paleontologist, part musician, and part retro-computing enthusiast. We even visited him later in Paris, where he showed us his amazing chip collection. Antoine has now become a member at large of our little team.
So, you know that we have had a run-in with those previously on the channel. But the reason I want to do it again, is because I want to revive the HP version of those floppies. There is the 9885, which was introduced specifically to support Mr Fancy Pants' favorite machine, the HP 9825. You get it, right? 9825, 9885, they go together. And then, it evolved into this big monster, which is the 9895.
And that one is meant for the mini-computers, the small mainframe machines that they had. It has an HP-IB interface, which means it can connect to almost everything. It's a little bit of a universal floppy, which is why it's very interesting to get one. And I lucked out, because I got a pile of them during my last haul from LA. It was a few years ago, so it's about time we start working on them. So, inside of that big monster of a 9895 unit, there are two drives, also monstrous.
And I have taken one out over here. So that's the HP one, and actually, this is one of the original IBM ones. We should talk about this one first.
So you might, or might not know, that the floppy was invented by IBM. It was already introduced as a read-only media, so they could load their boot microcodes in their bigger machines. Distributing microcode had always been a problem, this was actually a cost reduction for distributing firmware. They eventually made a read/write version that a customer could use.
And this one is one of the early ones. This is a 31 SD, and you can see it has a single head. This is just a pusher.
So this is a single sided disc, and it's also single density. But the early ones don't have DC motor, they have an AC motor that's always on. And then you have another huge motor, which is the stepper motor. So that's the stepper motor to move the head, and that's the motor to spin the disc. They have this proprietary interface. And next to the IBM, I have put the HP version.
It's actually not HP, they bought it from somebody else. You can see it's similarly built: it has this huge AC motor, and it has this very large stepper motor. But here, it's double headed: there's a head on the top and on the bottom. And also, while I'm telling about single-sided low density drives, and this double-sided drive, I have to mention that there are four different types of floppies.
This is the original one, Type 1, which later got called single-sided single density. So this one has only one side, and it can hold about 300 kilobytes. Then IBM came up with a Type 2. It says diskette 2, and this one just has two sides. So it holds double the amount, so that's about 600k.
And then, they came up with their next trick, which consisted of changing the encoding, and they reached double density. They needed better media to do that, so this is a Type 2D, the double-sided double density, which now has a very respectable 1.2 megabytes of data. And there was a money pincher somewhere that also invented the single-sided double density. So I've taken the double [sided] and a single [sided] out of their pockets. The index hole in the double-sided is off to the side, whether the index hole in the single-sided is closer to the center.
So that's how you can tell. This is a little hole that comes once per revolution, and tells where the track begins. This one can only do the Type 1 diskette, so, single-sided, low density.
This one is actually a universal one. It can do single-sided, double-sided, low and high density. Also, this one has now the standard Shugart 50 pin interface. That's from Al Shugart, who is the person that headed the team that developed the original floppy. And then, when he went on his own after IBM was forced to open up their ecosystem, he standardized the interface.
And it's called the Shugart interface, and we still use a descendant of that in the modern floppies. So theoretically, since this HP drive, which we’ll see is not an HP anyhow, has a more or less a standard interface, we should be able to hook it up to a PC to test it. However, it turned out to be quite difficult, and we’ll show in the rest of the video how and why we had to develop a complicated adapter cable.
But here is the good news: Antoine has transformed this unwieldy cable into a nice little adapter, available on Tindie. On one side of the adapter, it has the 50 pin edge board connector for the 8 inch disk drive, and on the other side, a regular 34 pin connector that will plug into your computer floppy cable. It still has a whole bunch of options that have to be jumpered carefully, but Antoine has made a manual for that, and in this video will explain all the silly details. By the way, that’s the same adapter that Adrian used to connect his drive to a PC in his 8 inch floppy video. So we have proof that it works for more than just us… But yes, you can connect an ancient 8” drive to a PC, and boot from it. I think it's booting! Welcome to Dos on an 8 inch floppy diskette! Directory.
Tada! And so, this one is maxed out, because I put Donkey Kong on it. It's loading. And if you really want it, you can play your favorite DOS game right from the diskette. See how far I make it. Probably not very far... Ah! Or use it from within Windows 98 instead of a boring 3.5” floppy.
We are of course going to use this for an entirely different purpose, to test our HP drives, and to recover and recreate old 8” disks in non-native PC format. So, here is the story of how we did it. It starts quite a while ago, when Antoine was visiting, and Carl had not yet moved to Florida. [Marc] Flexible disk memory.
It's not hooked up to anything. And here is the power. [Carl] That's an interesting sign. And this looks like it's not flush, so it might even be... [Marc] Yeah, this one moved.
No power up test, drive one. So that one is not happy. [Antoine] It let the magic smoke escape? [Marc] It's time to extract the drives, and do some inspection and cleaning. So, what we have figured out so far. That's how the heads load.
This, we have to unbend, because the thing is all bent downwards. I want to clean the heads. So, this is a CDC drive apparently. Where was it written? It's Magnetic Peripherals, Inc. Control Data Corporation.
This is Oklahoma City Operations. This is from Oklahoma! This definitely had seen better days. There we go.
That was very needed. Oh, it binds. What binds? Antoine just found what's not right. And there is a little piece of plastic that's broken. And that's broken in three out of four motors that we have checked so far.
So it's an endemic problem. Then at the back, it needs - we have the mains, which is the beautiful safety proof everything. And here you have 24 volts at 5 volts. [Marc] Smoke test? [Antoine] Smoke test! [Marc] But I push it like this. [Antoine] Yep.
[Marc] And this is aligned. [Antoine] Yeah, and it's good. [Marc] 600 milliamps, no smoke.
24 volts, 42 milliamps - so, nothing. [Antoine] Yeah, that's good. [Marc] We're spinning! Okay, try to hook it up to the computer? [Antoine] I guess so, next step! [Marc] And that’s where things started to get more difficult. See, the original 8” Shugart interface has a 50 pin connector, and is fairly well thought out. But later on, the interface was condensed to make it fit on a cheaper 34 pin connector, which is this pinout.
And then, horrors of horrors, the IBM PC folks introduced the ignominious cable twist. That was very much in keeping with the spirit of the original PC, which was a bunch of hacks hastily cobbled together rather than a properly engineered machine, which later caused endless suffering. Anyhow, I had to come up with a way to fit 50 pins into 34 pins, and after a bit of head scratching, I came up with my own ignominious one day hack, back when we were trying to read our fossil data diskettes for our scientists. Mind you, just like the PC, it looked quite bad but worked quite well.
So, I figured, it should just be a simple case of reusing the same cable with our HP drive, and we’d be up and running in no time. [Antoine] Here you go, it's just a bit stiff. [Marc] In Dolch we trust. So from previous experience, our cable should be good.
But will the drive appear as A or B? With the various BIOS settings, the drive’s unknown configuration and the ignominious PC cable twist, it’s anyone’s guess. But if the BIOS is configured for both drive A and drive B, it should attempt to seek either drive at boot. Okay, there you go. We are powered up. Floppy disk fail! Floppy disk fail is not good, but it could be just that we configured it as the wrong thing in the BIOS, or the computer controller can’t recognize 8” drives.
More worrying though, is that we did not hear the drive seek. But I didn't hear it! Here, the splash screen says Windows 98, but I am just booting to the pure DOS stage. So I can run my favorite DOS tool, Omnidisk. Okay, Omnidisk.
Oh, drive one, there you go. Seek 20. [Antoine] Huh.
[Marc] Times out. [Antoine] No, it did not do anything. [Marc] Scan. [Antoine] Not happy! [Marc] No. So, try number two with the other disk drive, which doesn't have the plastic part broken. [Antoine] The ejection mechanism is better too.
[Marc] Right, yeah. [Antoine] Mains? [Marc] Uh, yep. [Antoine] Alright! [Marc] Okay, smooth. We just had a seek, I didn't capture it! OK, this drive is more promising, it seeked during the early BIOS boot process, as it should. And then while I was issuing seek commands with Omnidisk, something happened. [Carl] Did this just go? Do it again, with a higher level.
[Marc] Drive 1, seek, like 60? [Carl] No, what I meant was, go back to drive 0 and do the seek to a higher level. [Marc] Drive 0. Ah! [Antoine] Oh yeah. [Carl] So they're both drive 0. [Antoine] They're both A! So that's the jumper, it's hard wired there on the board.
[Carl] Yeah. [Marc] Okay, all right. All right, we got some action.
But apparently both my internal drive and the 8 inch drive think they are disk A, which is drive 0 on Omnidisk. So that’s an issue. We are having some better luck.
We disconnected the internal disk drive, so now I can seek to 60. Yay! Seek to 0. All right! [Antoine] But also, are the heads... I wonder if the heads are loaded or not? [Marc] Ah, I didn't load the head. Okay, so we're missing a signal probably.
[Antoine] Yeah. Yeah, there's probably something extra with the head load. [Marc] Right. So, the seeking works, but then, it can't read any signal, because there is no head loaded, nor, probably, the read amplifier is not engaged. On your other disk, it worked all by itself, right? [Antoine] It was more modern, and also the motor was turning on and off. [Marc] Yes.
[Antoine] So it did not add any wear on the disk because of that. This one had to implement something different, because the motor is always on. So they are limiting the wear on the disc by loading the head. [Marc] Or I should I do motor on, and should that load the head? Aha.
The 8 inch drive we had tried before was more advanced and PC compatible. Like a more modern drive, the heads are simply dropped on the disk after insertion by the door lock handle. Then the computer just turns on a low voltage DC motor to spin the disk when it wants to read it. But our CDC drive is way older and has an always-on AC motor.
The the heads need to be loaded by the PC 'Motor On' signal instead. But I thought I had wired that. [Marc] So, we are making some forensic progress here. We found what our drive is: it's a Control Data Corporation model 9406. And it has a whole freaking bunch of options on here. And here are the million options.
They are not on switches actually, they are configured permanently, either on or off. So, there's this one, there is this, there is that. When the little things are open, the option is off. When it's continuous, the option is on.
It tells you also what default configuration they have. And it turns out, ours is not the default configuration. It's head load with 'In Use' instead of the 'Head Load' signal.
And then, somewhere else, we found that 'In Use' is on pin 18. No, sorry, 'In Use' is pin 16. And, on the cable I made, we have connected the regular connection, which is pin 18, which is 'Head Load'. You'd use 'Head Load' for head load.
And what the HP drive uses, is 'In Use', which is pin 16, which is not connected. Therefore, we're going to put a manual switch on it. So here's our modified cable. And that is pin 16, and that should do 'In Use'.
And so, one of this positions should load the head. Hopefully. We think. [Antoine] Everything's connected.
[Marc] Okay. So you want me to try to do the head? [Antoine] Yeah, let's do it! Oh! Do it again? [Marc] It did the door lock! It didn't do the head. [Antoine] It does the door lock, the LED in on.
[Marc] Oh, because it's not selected! [Antoine] Ah... [Marc] So, what I'm going to do, is actually lock it, put it in use, and see if that will allow me to access it now from Omnidisk. [Antoine] Oh, it's loaded! [Marc] Oh! [Antoine] It just did load.
[Marc] Excellent! Oh, I have 0.8 amps on the 24 volts, so now it's... [Antoine] Oh, it just seeked! [Marc] Yeah so... [Antoine] There it is! There is the data! Oh! [Marc] We got it! [Antoine] We got it! It just had to seek. So, it was timed out from the...
[Marc] No, it just got it for [head] 1, 26 sectors. It got the 26 sectors. Oh! This one is only one head! [Antoine] Yep, it's a one-sided disc. [Marc] Right! You think I can use image disk and it will read it? [Antoine] Oh, let's try it. [Marc] IMD. Okay, Settings - S. Drive A. Cylinders 77.
Read disc into file. Oh yeah! [Antoine] It does stuff! [Marc] It's working fine At this point, we got it working in reading, but it would not be fully operational until Antoine developed the final adapter. It is available to everyone on Tindie, and comes with jumpering options, to address the differences between 8 inch drives and their later 5-1/4 inch cousins. There are over 11 areas where 8 inch drives differ, and think I got in trouble for every single one of them. So it’s worth spending some time looking at the adapter in detail.
Here is the schematic of Antoine’s adapter, with the standard 34 pin floppy connector to the PC on the right, and the 50 pin connector to the 8” floppy on the left. Half of the pins are ground, so we can ignore these. Let’s go through the signals that connect easily first. SS is head select, which connects to the pin of the same name on the other side. The PC generates the correct signal to toggle between the upper and the lower head. However, this brings us to the difference number 1: some 8” floppies are single sided, and others are double sided.
Drives that support both standards will detect what type is inserted, thanks to the location of the index hole. The drive will then indicate which type of diskette is inserted, using pin FD2S. However, there is no support for single sided drives on the PC, so we leave it dangling.
In fact, a PC will get very annoyed with a single sided disk, thinking it lost the signal from one of the heads. The only way to read and write single sided disks on a PC is to run specialized tools like ImageDisk. Next is the RD line with the read data. There is an equivalent on our drive, so no issue here. Nest, WP is the write protect signal.
It also connects straight through. However, beware of difference number two. Write protection works reverse on 8” floppies. On an 8 inch floppy, a disk is write protected when there is no tab across the notch. You can only write to it when you cover the tab with a sticker. Which is of course the exact opposite of 5-1/4 PC disks . Guess how I found out.
Moving on, Track 0, Write Enable and Write Data connect right across, so no problem with these. Same goes for Step and Direction. These are the lines that control the stepper motor to seek the head.
These two lines make it very easy to check if a drive seeks, you don’t even need a computer. Just shortly ground the STEP line to the ground, and the head should move one step, with the direction depending on whether the DIR line is grounded or not. The index line provides a pulse every time the index hole passes in front of the photodetector, and marks the start of the track. No problem here, it connects to the equivalent line.
Now, we come to difference number 3, which is a vexing one: drive selection lines. On the 8” floppies, there are 4 address lines, so you could have 4 of them connected to a single controller, as A, B, C and D drives. But on the PC side, it is a royal mess. PCs have only A and B drives. To make things worse, PC designers hijacked the two remaining address lines to make them motor control lines.
So we have Motor A, Drive Select B, Drive Select A, and Motor B. But wait, that is only if you have a straight cable! The PC designers decided that it would be an unsurmountable task for a user to configure a drive with a clearly marked jumper, so it would respond to the A or the B select line. In their infinite wisdom, they decided that all drives would be jumpered to the same default, as drive B. Yes you heard right, the default is B, not A. Remember, that’s to make life
simpler for us, the ignorant users. So to make a drive appear as an A drive, they used a cable with a twist, which inverts the A and B lines. So, when the computer tries to access the A drive, unbeknownst to it, it actually triggers the B lines through the twist, and the B drive responds as an A. Which is obviously much
better for the user, which life will be improved by this great decision, because it is not confusing at all. So, in order for our external 8” drive to respond as drive B, and not conflict with our internal drive A, one possible way is to use the B line and a straight cable. Then we put a jumper on Antoine’s adapter in the DS1 position.
This will connect the signal to the DS1 address select on the floppy. We then need to configure our floppy to respond to the DS1 address. In our case, this was accomplished by flipping the second microswitch here. Alright, now we got the address select sorted out.
But what do we do with the motor B line? This is difference number 4: early 8” drives, including ours, do not have motor control, it’s always on. Instead, they control the loading and unloading of the heads. Fortunately, Antoine thought about it. The motor B wire gets routed to two jumper blocks, giving you the option to wire it to Head Load, or Door Lock, or both.
If our drive had the default configuration, the wires would have done what they said, and by connecting the Motor On to Head Load via the header, we’d be done. But sadly, it did not, far from it. It had many configuration changes from the default. In fact, every highlighted line differs from the default. And what about the Door Lock then? That’s difference number 5. In the old 8” drives, you need to activate a mechanical door lock while you access the disk, so you can’t accidentally remove the disk while the heads are loaded.
This also prevents from changing the disk without the OS knowing about it. The door lock feature got removed for cost reasons on the PC drives. But in an 8” drive with loaded heads, you would certainly want to jumper the Door Lock header. Our case was more complicated. Our drive had an optional In Use line connected to pin 16, which had complicated internal logic from other signals, so it could decide on its own when to lock the door, light the LED, and load the heads.
So, long story short, after I deciphered the super complicated options, the way to make our drive work was to jumper the Door Lock header. Next comes the Disk Change wire. That is difference number 6. The original 8” drives are straight shooters: they know when the disk is in, and when the disk is out. And since they have a door lock, they can enforce that the disk is not taken out at the wrong time.
So they just report Disk Ready if there is a disk in there, and Not Ready if it’s not there. I like that. But we already saw that the door lock feature was deleted on PCs. So, knowing there is a disk in there is not enough, it does not guarantee it’s the right one. It could have been changed for another disk at any time. So the PCs introduced the disk change signal instead.
This signal is only active the first time the drive is accessed, if the door has been opened and re-closed, and a disk is present. Same happens if a power reset has been detected. After that, it becomes inactive for all of the next disk accesses. This way, the OS can detect if a disk has been changed, and it does not need to lock it. So the correct jumpering on a PC, is always to Disk Change. By the way, a PC will get hopelessly confused if you jumper it to the disk ready signal instead - it will think that you are keeping changing the disk over and over, and it will give you the “Disk Not Ready” error, even though there is clearly a disk in there.
Next comes difference number 7: write current, controlled by the TG43 pin. On early diskette media, the write current had to be reduced on the inner tracks, past track 43. That requirement disappeared when better magnetic media became available. So this obsolete signal got hijacked by PC drives, to deal with the dual density drives, forcing the drive to change speed for the appropriate disk type.
So we leave that one unconnected. Phew! That’s it for the adapter settings. This is tragically complicated. But wait, there is more! We have four more quirks to deal with. Issue number 8 is the pull-up resistors. When these disk drives were invented, there was no such thing as a tri-state bus.
Instead, they used pull-up resistors to 5V on shared lines. But there is an issue with that. Early drives used very low 150 Ohm pull ups. Most modern PC controllers can’t drive enough current to pull them low. And sure enough, our drive schematics showed the infamous 150 Ohm pull ups, so I needed to change them. They were all contained in a small array package that looked like an IC.
But looking closer, the resistor pack was not original, it had an HP number on it. HP had already switched them to 600 Ohm resistors. However, if your diskette has 150 Ohm pull ups, you will likely have to replace them with something higher. Next issue on our list is number 9, the 500 kHz bit rate. PCs support different bit rates depending on the diskette density.
The low density diskettes spin slower and run at 250 kHz. We need to force the PC to expect 500 kHz instead, or it will give us the dreaded Floppy Fail error. However, that’s easy to accomplish: you just need to set your BIOS to expect a high density 1.2M floppy on B, not a 360k. The high density floppies have the same rate of 500 kHz, so this will do the trick.
No more Floppy Fail at boot. On to issue number 10: FM modulation support. That refers to the scheme used to encode the bits on the drive. The original Type 1 single density 8 inch floppies used FM modulation. This is what our IBM disks from the fossil episode had.
Unfortunately, not all PC floppy controllers support this ancient format. On my Pentium II Dolch, the controller is able to read FM discs, but I cannot write to them. So I was still able to recover our paleontologists’ data, but I could not recreate an old FM disk image for an IBM mainframe with this setup. And last but not least on our list, difference number 11: the number of tracks, or cylinders as they call them, which is simply the number of positions that you can move the head to. PC disks have either 40 or 80 tracks. But 8” disks have neither: they have 77 tracks.
So, you have to be a little bit careful, because they have only 77 tracks. You have to tell the program. So this is IMD, ImageDisk, which is one of my favorites. And here, if you want to work with a diskette to make an image, the first thing you have to do, is go to Settings. And 'Drive', you change it to B, because it's on the B drive.
And here, 'Cylinders', you have to go to 77 here. Make sure it doesn't try to seek beyond that. Sides, this is double-sided, double step off. And now you should be good to go. If I do 'Read Into File', Test, Insert Disc to Read...
And now, it's going to happily do the read of the diskette. So I'm going to abort that. So, for Omnidisk, it's similar.
You have set it for Drive 1, that's the equivalent of Drive B. You want to tell it, it's 77 cylinders. We're going to map it. And scan. It's going to find out what's on the diskette in terms of cylinders and sectors and encoding. So it's an MFM disk, with 15 sectors. So it's a DOS disk.
So, same thing, you have to tell it it's 77 cylinders. Which brings us an interesting thing. What if you want to play with it in your PC, and want to format it? My favorite utility for that is NFORMAT. You want to choose 1.2MB and you want, to edit it, and make sure you change that to
77. And that's all you have to do. So now, it knows it has 77 tracks, it's down to 1.15 MB.
And press the key, and it should go, and format the thing. If you don't have any of those tools, you can still do it from DOS. You do FORMAT B: /F:1.2. We format it as a 1.2MB diskette. So DOS will do it. But at the end, and I don't like that, it just bumps the head.
Now you can hear it bumping. No sectors there! But it will still complete, it will still do it. It's just fine.
It's not elegant, but it works. And under Windows 98, it just appeared as a 5-1/4 inch floppy, doesn't know any better. So it's a 1.2 MB diskette.
And you can also format it from there. You just go 'Format'... And it will do the same thing as in DOS. It will start and it'll be fine, and then it'll bump the head into the stop when it goes past 77. You can hear it.
Actually it does a cleaner job than DOS, didn't insist too much. But then once you're there, it's just a regular disc. You use it like anything else you want. Let's put a music file. There we go. (plays the music) There you go.
So then you can just use it as a regular disc to your heart's content. Let's see if we can play Kong on an 8 inch diskette. It's loading! So, this is 1.2MB, so it's big enough for a game and the DOS installation minus the
sound drivers. I figured out it was more fun with sound. OK, start game. And I am absolutely horrible at Champ Kong as it's called. See how far I make it.
Probably not very far. [Game Music] Ah! Okay, I'm dead already. But you get it, you can run a PC off an 8" diskette, this is a pretty good format. [Windows 95 startup sound]
2023-01-17 17:27
