Thread
Write 800k Floppies?
I have an iMac-DV 400MHz G3. I need to write 800k floppy disks, and was wondering if anyone could provide input on what kind of USB floppy drive to get, and what app to use to write with. I have some disk images that I need to write for older stuff.
Thanks.
Thanks.
Sorry, not possible.
Mac 800k floppies use a physical method of reading and writing that is completely incompatible with PC floppy drives. All USB floppy drives are really just standard PC floppy drives, so they won't work with 800k Mac disks.
You'll need a "beige"-era Mac with a built-in floppy drive to read and write 800k Mac floppy disks.
(When Apple moves to 1.4 MB disks, they went with the PC standard method of reading and writing; but their floppy *DRIVES* still had to be compatible with their previous non-standard 800k and 400k disks; so while Apple's 1.4 MB drives can read and write any 400k, 800k or 1.4 MB Mac disk, as well as any 720k or 1.4 MB PC disk, the PC world didn't reciprocate.)
Mac 800k floppies use a physical method of reading and writing that is completely incompatible with PC floppy drives. All USB floppy drives are really just standard PC floppy drives, so they won't work with 800k Mac disks.
You'll need a "beige"-era Mac with a built-in floppy drive to read and write 800k Mac floppy disks.
(When Apple moves to 1.4 MB disks, they went with the PC standard method of reading and writing; but their floppy *DRIVES* still had to be compatible with their previous non-standard 800k and 400k disks; so while Apple's 1.4 MB drives can read and write any 400k, 800k or 1.4 MB Mac disk, as well as any 720k or 1.4 MB PC disk, the PC world didn't reciprocate.)
So does that mean that my PowerBook 150 can read 800k floppies?(When Apple moves to 1.4 MB disks, they went with the PC standard method of reading and writing; but their floppy *DRIVES* still had to be compatible with their previous non-standard 800k and 400k disks; so while Apple's 1.4 MB drives can read and write any 400k, 800k or 1.4 MB Mac disk, as well as any 720k or 1.4 MB PC disk, the PC world didn't reciprocate.)
Yes. And write them, too.
So, hold one here! If I say, hook the floppy drive up to a USB to IDE adapter, and the eject mechanism was somehow compatible, I could probably write 800k floppies? I think I might have a spare one from a busted 150... All I need now is a USB to IDE cable. Off to dealextreme.com!
The Powerbook 150 (and other Mac internal floppies) use a proprietary cable.
...and a proprietary interface. It's not even close to IDE.
Odd, you can put a standard 2.5 inch notebook hard drive in there. Would it be possible that it is IDE with pins switched around, sounds like a waste to have multiple interfaces in there.
No, it is not; I have looked at the insides of my (unfortunately) non-booting PB 150 and the interface is in no way like IDE. In fact, you might call it only used by Apple.
The hard drive is a standard 2.5" IDE device, exactly the same as those used in 90% of all laptops out there.
However, the floppy drive is a completely different matter, its the same interface as whats used on classic desktop Macs, just with a smaller, more PowerBook-friendly cable and connectors. The only drive you can plug in there is another floppy drive from another PowerBook. (PB150 needs manual inject, btw, such as those used in PowerPC 'Books) The interface has absolutely nothing in common with IDE, or even the PC floppy drive interface. As JRL said, its an Apple-only standard, never used by anyone apart from Apple.
However, the floppy drive is a completely different matter, its the same interface as whats used on classic desktop Macs, just with a smaller, more PowerBook-friendly cable and connectors. The only drive you can plug in there is another floppy drive from another PowerBook. (PB150 needs manual inject, btw, such as those used in PowerPC 'Books) The interface has absolutely nothing in common with IDE, or even the PC floppy drive interface. As JRL said, its an Apple-only standard, never used by anyone apart from Apple.
You seem to be assuming that the use of an IDE hard drive somehow implies that the floppy interface is also IDE. I don't know why you would make that association -- it would be unique among computers if it were so. A scsi-equipped mac does not have a scsi floppy drive; PCs with IDE hard drives have proprietary floppy interfaces that, although sharing a common heritage with IDE, are not themselves IDE.Odd, you can put a standard 2.5 inch notebook hard drive in there. Would it be possible that it is IDE with pins switched around, sounds like a waste to have multiple interfaces in there.
Floppy and hard drives have very different characteristics, and their interfaces evolved independently as a result.
And no, the 150's floppy interface is not just an IDE with "pins switched around." I really meant what I wrote earlier: The floppy interface in a Mac is nowhere near IDE in design.
Darn! With a small bit of hope left: is the floppy interface in a Mac like a floppy interface on a PC's motherboard? ?
Nope, not even close.
To my knowledge, the actual limitation isn't the floppy drive itself. That is to say that a PC floppy drive could read or write 800 kB floppies.
BUT
Old Mac and PC floppy drives are nothing like USB floppy drives. The old devices were low level devices that needed a special controller to do a lot of the work for it (e.g. telling the motor that moves the drive head when to start and when to stop).
This means that the floppy drive controller is not the only piece of hardware that you have to consider. The other piece of hardware that you have to consider is the floppy drive controller. So even if a PC and Mac floppy drive were electrically compatible (which they are not), you still could not hook-up a Mac floppy drive to a PC floppy drive controller and expect it to read or write Mac floppy diskettes.
BUT
Old Mac and PC floppy drives are nothing like USB floppy drives. The old devices were low level devices that needed a special controller to do a lot of the work for it (e.g. telling the motor that moves the drive head when to start and when to stop).
This means that the floppy drive controller is not the only piece of hardware that you have to consider. The other piece of hardware that you have to consider is the floppy drive controller. So even if a PC and Mac floppy drive were electrically compatible (which they are not), you still could not hook-up a Mac floppy drive to a PC floppy drive controller and expect it to read or write Mac floppy diskettes.
Sigh, Ok.
Also, from memory, the 1.4MB Apple drives can write 800k floppies, but not 400k ones.
They actually write 400k disks fine; just not in OS 7.6 and above.
Here you go:
Apple's floppy drives are unique in that they have almost no circuitry on the drive themselves. The drive is just a dumb set of motors and heads. The floppy drive controller chip resides on a board in the computer. This is true from the Apple II all the way up to the beige G3 and PowerBook G3. On the Apple II, it was an add-in controller card, on all Macs (again, up to the beige G3 and the last PowerBook G3 with a floppy drive,) it's on the motherboard. There is only one cable running in to an Apple floppy drive. This cable contains all of the 'raw' data pins, as well as the power to run the motors.
On a PC, much of the electronics are on the drive itself. The controller on the motherboard (or, on very early PCs, an add-in card,) is much simpler than the chip on a Mac. This is because the drive itself has some 'smarts' to it. This also means that the floppy drive needs its own separate power. The data cable carries not the raw 'straight-from-the-heads' data, but is similar in concept (if not implementation) as IDE and SCSI in that the data arrives packaged. (Note that even though my explanation is long winded, it's still technically simplified, so some things are technically inaccurate in the name of ease of understanding.)
The big deal here is that, for example, a PC that can only talk to a 720 KB floppy drive, is incapable of using a 1440 KB floppy drive. This is because the controller won't speak the same language as the drive. On a Mac, you can slap a 1.4 MB "SuperDrive" into a computer that only understands 800K drives, because the raw electronics in the drive are the same, only the read head's ability to deal with the newer disks is different. It's just that in an 800K-only computer, the drive will act exactly as an 800K drive, since the controller chip doesn't know about 1.4 MB disks.
The deal is that when Apple introduced the 1.4 MB controller chip, they not only added the ability to read and write High Density disks, but they changed the raw method in which the disks are read to and written from to be the same physical style as PC disks. Then all it took was software to be able to read and write PC disks. Unfortunately, because of the difference in the physical style of writing lower-density disks, PCs could not just have software to let them read Mac lower-density disks.
But, the ability to read and write older 400K and 800K Mac disks remained. My PowerBook 100 running System 6 has no problems reading my MacWrite 1.0 disk from an original Macintosh 128k.
Because the two mechanisms are so different (Mac vs. PC) anything[/i that assumes a PC-style floppy drive (wether an actual PC, or a USB floppy drive case,) will not work with a Macintosh floppy drive, and therefore, no Macintosh 400K or 800K disks. (In spite of the similar nature of notebook floppy drives on PCs vs. Macs, PC notebook drives still use the same PC floppy interface, only with a smaller physical plug; and Mac drives still use the same Mac floppy interface, only with a smaller physical plug.)
Finally, the PC floppy interface predates IDE (Properly called "ATA") by quite a few years, and is a completely separate interface. You can *NOT* plug a PC floppy drive (of any kind) into a PC ATA controller (of any kind.) (Just as you cannot plug a Mac floppy drive into a SCSI port.) It just so happens that many PC notebooks (and even a few Mac notebooks,) used the same physical 'expansion bay' for both floppy drives and hard drives or ATA optical drives. The electrical signal is 100% separate, though. They go through the same physical plug, but the physical plug carries both kinds of signals on different pins. The device plugged in is just wired to the proper pins. (This idea exists in the new notebook computer expansion card "ExpressCard", used on the MacBook Pros as well as many PC notebooks. The slot contains both pins for PCI Express as well as USB. The card manufacturer decides which set of pins they want to use. For example, I have a FireWire 800 card that uses the PCI Express pins, and a flash memory card reader that uses the USB pins. So in System Profiler, one appears under "PCI Express", one appears under "USB".)
Apple's floppy drives are unique in that they have almost no circuitry on the drive themselves. The drive is just a dumb set of motors and heads. The floppy drive controller chip resides on a board in the computer. This is true from the Apple II all the way up to the beige G3 and PowerBook G3. On the Apple II, it was an add-in controller card, on all Macs (again, up to the beige G3 and the last PowerBook G3 with a floppy drive,) it's on the motherboard. There is only one cable running in to an Apple floppy drive. This cable contains all of the 'raw' data pins, as well as the power to run the motors.
On a PC, much of the electronics are on the drive itself. The controller on the motherboard (or, on very early PCs, an add-in card,) is much simpler than the chip on a Mac. This is because the drive itself has some 'smarts' to it. This also means that the floppy drive needs its own separate power. The data cable carries not the raw 'straight-from-the-heads' data, but is similar in concept (if not implementation) as IDE and SCSI in that the data arrives packaged. (Note that even though my explanation is long winded, it's still technically simplified, so some things are technically inaccurate in the name of ease of understanding.)
The big deal here is that, for example, a PC that can only talk to a 720 KB floppy drive, is incapable of using a 1440 KB floppy drive. This is because the controller won't speak the same language as the drive. On a Mac, you can slap a 1.4 MB "SuperDrive" into a computer that only understands 800K drives, because the raw electronics in the drive are the same, only the read head's ability to deal with the newer disks is different. It's just that in an 800K-only computer, the drive will act exactly as an 800K drive, since the controller chip doesn't know about 1.4 MB disks.
The deal is that when Apple introduced the 1.4 MB controller chip, they not only added the ability to read and write High Density disks, but they changed the raw method in which the disks are read to and written from to be the same physical style as PC disks. Then all it took was software to be able to read and write PC disks. Unfortunately, because of the difference in the physical style of writing lower-density disks, PCs could not just have software to let them read Mac lower-density disks.
But, the ability to read and write older 400K and 800K Mac disks remained. My PowerBook 100 running System 6 has no problems reading my MacWrite 1.0 disk from an original Macintosh 128k.
Because the two mechanisms are so different (Mac vs. PC) anything[/i that assumes a PC-style floppy drive (wether an actual PC, or a USB floppy drive case,) will not work with a Macintosh floppy drive, and therefore, no Macintosh 400K or 800K disks. (In spite of the similar nature of notebook floppy drives on PCs vs. Macs, PC notebook drives still use the same PC floppy interface, only with a smaller physical plug; and Mac drives still use the same Mac floppy interface, only with a smaller physical plug.)
Finally, the PC floppy interface predates IDE (Properly called "ATA") by quite a few years, and is a completely separate interface. You can *NOT* plug a PC floppy drive (of any kind) into a PC ATA controller (of any kind.) (Just as you cannot plug a Mac floppy drive into a SCSI port.) It just so happens that many PC notebooks (and even a few Mac notebooks,) used the same physical 'expansion bay' for both floppy drives and hard drives or ATA optical drives. The electrical signal is 100% separate, though. They go through the same physical plug, but the physical plug carries both kinds of signals on different pins. The device plugged in is just wired to the proper pins. (This idea exists in the new notebook computer expansion card "ExpressCard", used on the MacBook Pros as well as many PC notebooks. The slot contains both pins for PCI Express as well as USB. The card manufacturer decides which set of pins they want to use. For example, I have a FireWire 800 card that uses the PCI Express pins, and a flash memory card reader that uses the USB pins. So in System Profiler, one appears under "PCI Express", one appears under "USB".)
With some laptop expansion bays the floppy drive uses a different connector for the floppy drive then they do the ATA drive - I know PB1400s have two connectors in the optical bay - one for ATA, the other for a floppy drive.
The floppy drive mechanisms in both cases are pretty dumb devices. PC floppy drives are actually dumber than Mac floppy drives -- about the only thing they can do by themselves is reset the heads to track 0 on power-up, and the bus they use is pretty much the same as the old Shugart SA400 from 1976 -- one step at a time, no direct control of phases. Apple 3.5" floppy drives have registers inside them for various things, I've forgotten what, so they're marginally smarter than PC drives. (I do know they use the stepper motor phases as a register select bus.)
The Disk II was the dumbest of all, having nothing more than the stepper motor and a head amplifier, and I think that's what Anonymous Freak had in mind.
Anyway, the real issue here is what the controller does with the data once it receives it. The IWM, just like the Disk II before it, is just a state machine that pulls raw bits off the disk and expects the OS to make sense of them. This makes it quite flexible; you could probably read an MFM disk on an IWM if you knew what bits to tweak. (I'm not sure what magic the SWIM chip uses for MFM, but I would imagine the reason it wasn't done sooner is that either the IWM or the Mac itself couldn't handle 500-kbit MFM data reliably.)
PCs, however, use a chip that traces its ancestry back to the NEC uPD765 that was in the original IBM PC/XT; specifically, they're variants of either the Intel 82072 or Western Digital 37C65 PC/AT floppy controllers, depending on whose Super I/O chip you have. The 765 is easy to program and supports DMA, but it's also incredibly inflexible compared to the IWM; it only supports FM or MFM in the standard IBM "midrange" formats, and all data appears "cooked" -- raw disk access is pretty much impossible without hacks, as is reading a disk that strays too far out of the IBM specs. It also expects to use the same data rate across the entire disk (CAV mode); Mac 800k disks are zoned CLV, making them even trickier to read.
Pretty much all USB floppy drives use this particular setup, as it's well-known and easy to implement using off-the-shelf parts, so reading anything "weird" on them is out of the question. There's also the odd LS120/240 drive floating around still; they're very fast in floppy mode, but also limited to MFM (though they don't use 765s as far as I know).
Back in the day, there was a piece of hardware, the Copy II PC Deluxe Option Board, that got around all this by cutting the 765 out of the loop and using its own custom ICs to process the raw bits coming off the disk. It could read practically anything if it knew what to look for. Unfortunately, they're kind of hard to find now, and would require an older machine with ISA to be useful. That said, I have one, and it does actually work once you find the utilities...
Failing that, your best bet is to use an older Mac as a go-between. One of the reasons I still have my 8600 is that it can read and write 800k disks for my ROM 0 IIgs. (That and my 475's floppy controller is messed up.)
The Disk II was the dumbest of all, having nothing more than the stepper motor and a head amplifier, and I think that's what Anonymous Freak had in mind.
Anyway, the real issue here is what the controller does with the data once it receives it. The IWM, just like the Disk II before it, is just a state machine that pulls raw bits off the disk and expects the OS to make sense of them. This makes it quite flexible; you could probably read an MFM disk on an IWM if you knew what bits to tweak. (I'm not sure what magic the SWIM chip uses for MFM, but I would imagine the reason it wasn't done sooner is that either the IWM or the Mac itself couldn't handle 500-kbit MFM data reliably.)
PCs, however, use a chip that traces its ancestry back to the NEC uPD765 that was in the original IBM PC/XT; specifically, they're variants of either the Intel 82072 or Western Digital 37C65 PC/AT floppy controllers, depending on whose Super I/O chip you have. The 765 is easy to program and supports DMA, but it's also incredibly inflexible compared to the IWM; it only supports FM or MFM in the standard IBM "midrange" formats, and all data appears "cooked" -- raw disk access is pretty much impossible without hacks, as is reading a disk that strays too far out of the IBM specs. It also expects to use the same data rate across the entire disk (CAV mode); Mac 800k disks are zoned CLV, making them even trickier to read.
Pretty much all USB floppy drives use this particular setup, as it's well-known and easy to implement using off-the-shelf parts, so reading anything "weird" on them is out of the question. There's also the odd LS120/240 drive floating around still; they're very fast in floppy mode, but also limited to MFM (though they don't use 765s as far as I know).
Back in the day, there was a piece of hardware, the Copy II PC Deluxe Option Board, that got around all this by cutting the 765 out of the loop and using its own custom ICs to process the raw bits coming off the disk. It could read practically anything if it knew what to look for. Unfortunately, they're kind of hard to find now, and would require an older machine with ISA to be useful. That said, I have one, and it does actually work once you find the utilities...
Failing that, your best bet is to use an older Mac as a go-between. One of the reasons I still have my 8600 is that it can read and write 800k disks for my ROM 0 IIgs. (That and my 475's floppy controller is messed up.)
Thanks for the very complete explanation, lee4hmz!
It may be of interest that the Outbound Model 125 reads and writes the Mac 800K format using a standard Citizen brand notebook floppy drive.
Of course there's a circuit board between the Citizen and the Outbound.
The main components on the circuit card are (IIRC):
WD 37C65
WD 92C32 (Digital Data Separator for floppies)
74LS624 (VCO)
XP9103 (digital potentiometer)
28C64
GAL16V8 (the part that holds me up cloning the thing)
and a few assorted 74 series logic chips.
Oh, yeah, and right at the input (host) end is an 85C30--makes me wonder what protocol the Outbound is using to talk to the thing.
One of these days I really need to whip up a schematic on this thing. It reads and writes 400K, 800K and 1.44MB format Mac floppies.
One kind of curious thing is that if my understanding is accurate, the 37C65 already has the functionality of the 92C32 built into it, so why the separate 92C32? I suspect that the VCO and the XP9103 are in some way used to control the motor speed of the floppy disk.
Other kind of interesting facts are that the Model 125 came out around 1990, uses the ROM of a Plus or SE and uses a standard IDE notebook drive (but only certain models). Arguably (or perhaps totally) the first Mac hardware to use an IDE drive.
Of course there's a circuit board between the Citizen and the Outbound.
The main components on the circuit card are (IIRC):
WD 37C65
WD 92C32 (Digital Data Separator for floppies)
74LS624 (VCO)
XP9103 (digital potentiometer)
28C64
GAL16V8 (the part that holds me up cloning the thing)
and a few assorted 74 series logic chips.
Oh, yeah, and right at the input (host) end is an 85C30--makes me wonder what protocol the Outbound is using to talk to the thing.
One of these days I really need to whip up a schematic on this thing. It reads and writes 400K, 800K and 1.44MB format Mac floppies.
One kind of curious thing is that if my understanding is accurate, the 37C65 already has the functionality of the 92C32 built into it, so why the separate 92C32? I suspect that the VCO and the XP9103 are in some way used to control the motor speed of the floppy disk.
Other kind of interesting facts are that the Model 125 came out around 1990, uses the ROM of a Plus or SE and uses a standard IDE notebook drive (but only certain models). Arguably (or perhaps totally) the first Mac hardware to use an IDE drive.
Sort of. The 92C32 and the VCO are there so the card can set an arbitrary bit rate (the 37C65 only supports the standard FM/MFM rates). That way, it can read 800k disks without changing the motor speed; PC floppy drives are built like HDDs, and are locked to a certain speed (usually 300 or 360 RPM). It's also, most likely, using the XP9103 as a cheap substitute for a DAC (I don't have a have data sheet handy for it, so this is pretty much a WAG...) to control the VCO.One kind of curious thing is that if my understanding is accurate, the 37C65 already has the functionality of the 92C32 built into it, so why the separate 92C32? I suspect that the VCO and the XP9103 are in some way used to control the motor speed of the floppy disk.
The Deluxe Option Board actually uses a similar trick, though they used a UMC data separator instead of a Western Digital.
-lee
Thanks for the analysis lee4hmz. Have you actually examined one of the Outbound floppies or is your analysis based on experience with your floppy adapter?
I'm always happy to find another person with experience of the Outbound Laptop Model 125.
I'm always happy to find another person with experience of the Outbound Laptop Model 125.
I've never actually seen the Outbound adapter, but I did find a discussion somewhere (I've forgotten where now) of how the DOB works internally, and judging from the chips that are on it, the Outbound's adapter board would seem to work the same way.Thanks for the analysis lee4hmz. Have you actually examined one of the Outbound floppies or is your analysis based on experience with your floppy adapter?
-lee