[HN Gopher] Emulating the Early Macintosh Floppy Drive
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Emulating the Early Macintosh Floppy Drive
Author : GloriousCow
Score : 83 points
Date : 2024-08-25 16:04 UTC (1 days ago)
(HTM) web link (thomasw.dev)
(TXT) w3m dump (thomasw.dev)
| GloriousCow wrote:
| An in-depth dive into the Macintosh floppy drive system,
| including the fascinating IWM (Integrated Woz Machine) custom
| floppy controller. The level of fidelity to properly emulate the
| Macintosh disk drive is impressive, and this should be an
| essential resource to any aspiring Macintosh emulator developers.
| tom_ wrote:
| Feels slightly surprising, at least from the comfort of my 21st
| century armchair, that they went to all that effort for 800 KB
| per disk. The Atari ST (with an off the shelf 1772 FDC) had no
| problem with 800 KB - 2 sides, 80 tracks, 10 sectors per track,
| 512 bytes per sector - and that seemed perfectly reliable.
|
| The Amiga did its own thing, same as the Mac, but at least it got
| some extra storage. 880 KB per disk!
|
| (880 KB was also an option on the ST, but only for disks written
| a track at a time, which was impossible to guarantee if using the
| OS. With 11 sectors per track, writing individual sectors wasn't
| reliable as the gaps between them are so small. The OS didn't
| support irregular disk geometry so you couldn't have more sectors
| on the outer tracks.)
| brudgers wrote:
| Per Wikipedia, early ST's floppies were 360K even though it
| came out a year after the Macintosh.
| https://en.wikipedia.org/wiki/Atari_ST#Floppy_drive
|
| Hardware got better really quickly in the 1980's and 90's,
| including floppy disks. By the end of the 20th century, there
| were 120MB floppies. Basically Moore's Law seemed to apply to
| spinning rust for awhile.
| chuckadams wrote:
| > By the end of the 20th century, there were 120MB floppies
|
| In the form of Zip disks, yes. I'm reasonably sure 3.5"
| disks, the last thing to be called "floppies", topped out at
| 2.88M.
| wtallis wrote:
| LS-120 drives were floptical drives that were backwards-
| compatible with 3.5" 1.44MB disks. IIRC you needed special
| media to use the 120MB capacity, but the same slot could
| accept the common 1.44MB disks and give you much better
| performance than normal floppy drives. The successor LS-240
| drives also had the ability to write 32MB to a standard
| floppy disk using shingled magnetic recording.
|
| If Zip disks, CD-R and USB flash drives hadn't showed up,
| these drives would have been pretty widely recognized as
| the next generation of floppies.
| chuckadams wrote:
| Right, I forgot about flopticals... but I guess almost
| everyone else did too. NeXT boxes had those, didn't they?
| wtallis wrote:
| NeXT boxes used magneto-optical disks, which usually
| meant a laser was used to heat the magnetic material
| during the write process, and at lower intensity to read
| data optically. The optics in a floptical drive are just
| part of the head alignment servo mechanism, so it was
| probably much easier to make them cheap and backwards-
| compatible with mainstream floppies.
| wazoox wrote:
| Nope, NeXT had magneto-optical 128 MB drives, somewhat
| related. They were 3.5" but using an entirely different
| media, and were absolutely incompatible with ordinary
| floppies.
| ForOldHack wrote:
| NeXT cubes used a 256 Mb optial drive, and some slabs
| has. 128Mb optical, and someone said that the turbo color
| slab had a 230Mb optical drive. Mine did not.
| wazoox wrote:
| Yes, and the Cube came first with _only_ the slow MO
| drive, no hard drive because it wasn 't "high tech"
| enough for Steve Jobs :)
| brudgers wrote:
| Almost all digital formats die in obscurity. 3" floppies,
| 5v SmartMedia, Jazz disks, and DAT were good ideas in the
| moment that were not good ideas a moment later. The
| logistics of reading even popular formats like Qic 40 and
| ADAT today are hard.
| NikkiA wrote:
| The most ironic thing, IMO, is that at the time everyone
| seemed to be holding their breath for Castlewood's 'Orb
| drive', which promised the perfection of a fast and big
| storage media.
|
| It was delayed so long that by the time it actually
| reached the market it didn't get noticed.
| rasz wrote:
| Op meant LS120.
|
| "Ordinary" floppies peaked in 1988 (yes, before IBM 1990
| PS/2 2.88 ED) with 'Triple' or '2TD' format developed and
| shipped by NEC inside PC-88 VA3. 13MB unformatted, _9,120
| kB_ formatted capacity. Triple because it tripled track
| density from 80 to 240 while reusing ED barium ferrite
| magnetic media and perpendicular recording head of ED
| drive, same ~100KB/s speed.
|
| https://necretro.org/PC-88_VA3
|
| https://en.wikipedia.org/wiki/List_of_floppy_disk_formats#:
| ~...
| NikkiA wrote:
| There was also the Sony HiFD Which was 200MB and used the
| same form factor disks as FDHD drives, thus maintaining
| compatibility.
|
| It had a 'click of death'-like failure like Zip did though,
| and lost the battle during its recall and redesign. (IOMEGA
| were lucky in that the click of death didn't really kill
| Zip's market until about the time that CDR/CDRW was beating
| them anyway)
| thought_alarm wrote:
| It's all just an evolution of their existing disk drive
| technology that started well before the last-minute decision to
| go with the Sony 3.5" drive.
|
| The variable drive speed comes of the development of the
| "Twiggy" drive, which was an 850 kB 5.25 disk format originally
| intended for the Apple III in 1980 but never worked reliably.
|
| BTW, the Atari ST uses the same floppy disk format as the IBM
| PC, 360 kB per side.
|
| The Amiga uses a variable drive speed like the Mac, but they
| eke out extra capacity by eliminating sectors. This allows an
| extra 512 bytes per track, but the trade off is that the disk
| controller can only read or write an entire track at a time,
| rather than individual sectors.
|
| An infamous Apple II copy protection scheme used the same trick
| to expand 5.25 disk capacity from 16 sectors to 18 sectors (512
| bytes per track).
| tom_ wrote:
| 360 KB/side was indeed the default for the Atari ST, but
| there were numerous tools (I think Fastcopy III was the one I
| usually used) to format with more sectors per track, and 10
| sectors/track (so 400 KB/side) was the standard
| recommendation if you just wanted more data per disk and no
| hassle. More than 80 tracks was also an option, and 81 or 82
| tracks was apparently also reliable. That never sat right
| with me though, so I didn't do it.
|
| (18 sectors per track with 256 byte sectors is also possible
| with the 1770 series. This was one of the disk format options
| on the BBC Micro. Definitely not written a track at a time!
| There just wasn't the memory for that.)
| rasz wrote:
| >Amiga uses a variable drive speed
|
| Amiga uses standard PC drives with slight tweaked pinout
| https://linuxjedi.co.uk/2020/12/05/converting-a-pc-floppy-
| dr...
| s800 wrote:
| The Amiga is fixed RPM or CAV, not CLV like the og Mac. With
| one exception- later models could halve the RPM to read/write
| HD floppies (1.44MB PC or 1.76MB Amiga).
| ForOldHack wrote:
| You only read the data sheets. The twiggy drives had 4 heads
| to cut latency and had two access windows one in the back
| like all 5.25 and one in the front for the extra heads. The
| Lisa used this too.
| sumtechguy wrote:
| With some PC drives you could push the cylinders and sectors
| and get the same size. There were a couple of utilities out
| there to do it. However, not all PC drives were alike. So you
| could do that on your machine and your buddies machine would
| not read it at all.
| joezydeco wrote:
| Andy Herzfeld explains the backstory of the Mac disk drive in
| that classic Folklore.org story:
|
| https://www.folklore.org/Hide_Under_This_Desk.html
| Lammy wrote:
| > The disadvantage of this technique was that there was no
| interoperability with PC diskettes possible, at all, even with
| software changes. For the Macintosh, this changed with the
| introduction of the Macintosh SE in 1987. The Macintosh SE had a
| new floppy drive controller, the 'SWIM' (Super Woz Integrated
| Machine) and a new disk drive which could read and write both
| Macintosh CLV and PC CAV formatted diskettes.
|
| Pardon my nitpick, but there were two versions of the SE and the
| author has the dates mixed up here. The original 1987 model had
| the same disk capabilities as the Mac Plus except it could have
| two of them installed internally instead of just one on the Plus.
| Or one 800K drive and an internal SCSI HDD in the other bay --
| your choice! (Mine actually has all three thanks to a third party
| internal HDD bracket!)
|
| The FDHD (floppy disk high density) version was released in 1989
| as a standalone computer and also as an upgrade kit for the
| original model containing one (1) SuperDrive, SWIM, updated ROM,
| and little "FDHD" and "800K" badges to put next to the upgraded
| and remaining original drives respectively.
|
| See https://bylenga.ddns.net/FDHD/MacSEservice.pdf#page=87
| ForOldHack wrote:
| SE and SE HD, and if you took the 400 or 800k version of the
| second floppy from your Mac plus, you could use it as a third
| floppy. I tried this on an SE and it worked, but never tried it
| on a SE HD. I thought that some early MacIIs had iwm chips in
| them, and with A FD HD upgrade you got a SWIM chip and a pair
| of ROMs to put in.
| hnpolicestate wrote:
| Got myself 3 iMacs (1998) and 2 Macintosh SE's (not sure specific
| model yet) yesterday at an estate sale for $50.
| memcg wrote:
| I was given a Macintosh SE model M5010 and a M5011 in 2020.
| Both have bad hard drives, but the batteries are not leaking.
| I'm not sure when I'll get around to working on them.
| lisper wrote:
| Does anyone make a usb floppy drive capable of reading Mac disks?
| I would be willing to pay quite a lot for one.
| Locutus_ wrote:
| If you have important Mac disks to archive, then a Kryoflux is
| probably the way to go.
|
| It's a external USB attached floppy drive controller that uses
| a normal PC floppy drive.
|
| It reads the raw disk stream and software then decodes that for
| whatever disk format it was. It seems old Mac disks can be
| recovered with it:
|
| https://www.kryoflux.com/?page=home
| http://forum.kryoflux.com/viewtopic.php?t=135
| Lammy wrote:
| Also https://github.com/keirf/greaseweazle
| lisper wrote:
| Thanks!
| ForOldHack wrote:
| There are two sets of kryofluxed floppies on archive.org. the
| 800k image is 58Mb, and all four floppies have errors at
| 60~65%. All the data is extractable except for the bad
| regions so... It looks like they kryofluxed the disks to
| preserve what data they had left, but it's not a solution.
| It's a huge waste of space, can you imagine a box of disks
| all inflated to 73 times their size?
|
| Apple got Sony to make cav drives, (MacIIx and SE HD to the
| 9600 )and when they raised the price, no floppy. Sneaker net
| was over until USB drives became cheap.
|
| One disk on archive that is unrecoverable is Adobe Type
| Manager. The areas where the fonts are is corrupted, but the
| data is available elsewhere, but the program isn't.
|
| Now it sits in the cloud ( someone else's hard disk ) in a
| corrupted state. Wish I had an SE 30 to restore the disk, and
| put it's compressed image up as a replacement.
| ForOldHack wrote:
| It says 800k/400k, but all his images are 800k. The
| filesystem may be different, but for diskcopy 4.2, it never
| made a difference. ( MFS vs hfs ). I am sure that for
| kryoflux, it does not make a difference either.
|
| It does not show how kryoflux assists in recovery. They can
| be archived, and preserved, but not recovered. ( Just try the
| 800k ATM disk on archive.org )
| ForOldHack wrote:
| There were USB drives that sold for iMacs,but the ability to
| read MFS (400 and800k) floppies disappeared soon afterwards..
| zydeco wrote:
| As far as I recall, none of the USB drives of the iMac era
| could read 400/800K GCR disks, they were PC drives that could
| only use 720/1440K disks. The Imation SuperDisk drives could
| also use their own 120MB "floptical" disis. Later versions
| extended it to 240MB, and could also write 32MB to a standard
| floppy disk. MFS refers to the file system used on 400K
| disks. 800K disks used HFS.
| mmmlinux wrote:
| The easiest solution is get a late model vintage mac that still
| has a floppy drive. the late model drives can read pretty much
| all mac floppies. the machine will be able to image the disk
| and copy it to usb(pci usb card) or over a network.
|
| Or you can get something like a Greaseweazle[1] and go that
| route if you want to do more advanced extraction.
|
| [1] https://github.com/keirf/greaseweazle
| userbinator wrote:
| It's interesting how much of the (latency sensitive) data
| processing is done on the main CPU; I've not used early Macs
| much, but given they have a multitasking GUI, would user input be
| noticeably delayed during disk activity, or could it cause
| problems to e.g. move the mouse rapidly while it was accessing
| the disk? 16 CPU cycles per bit sounds like it wouldn't leave
| much time for anything else.
| camhenlin wrote:
| Early Macs are not really multitasking in the sense that newer
| machines are. Each running application has to hand back control
| to the operating system as a part of its main loop (think like
| video game main loop if you are familiar with that)
|
| In the same way, disk operations themselves are generally
| blocking and will hand back control to the OS and apps during
| their read/write cycles so that other things can happen on the
| computer.
| wmf wrote:
| Hard real time was pretty easy to do on the Mac because you
| could run code in interrupt handlers. For example, dragging the
| mouse (e.g. to pull down a menu) suspended all processing in
| the system so that it would be responsive. The floppy driver
| might have run at an even higher priority, causing the mouse to
| skip during I/O.
| bogantech wrote:
| On my Mac Plus the cursor lags horribly when the floppy is
| being accessed
| ForOldHack wrote:
| Yes! You got the icon with the oval windows! Now try this in your
| emulatiom: if you named a disk '.Sony' you can kiss the data good
| bye. The drivers name is '.sony' too. Someone named their hard
| disk '.' and that was the beginning of multiple software
| problems.
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