Emulating the Early Macintosh Floppy Drive
thomasw.dev
Emulating the Early Macintosh Floppy Drive
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Re: Emulating the Early Macintosh Floppy Drive
#2An 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.
Re: Emulating the Early Macintosh Floppy Drive
#3Feels 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.)
Re: Emulating the Early Macintosh Floppy Drive
#4Andy Herzfeld explains the backstory of the Mac disk drive in that classic Folklore.org story:
Re: Emulating the Early Macintosh Floppy Drive
#5> 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.
Re: Emulating the Early Macintosh Floppy Drive
#6Feels 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…
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.
Re: Emulating the Early Macintosh Floppy Drive
#7Feels 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…
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).
Re: Emulating the Early Macintosh Floppy Drive
#8Feels 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…
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.
> 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.
Re: Emulating the Early Macintosh Floppy Drive
#9Got myself 3 iMacs (1998) and 2 Macintosh SE's (not sure specific model yet) yesterday at an estate sale for $50.
Re: Emulating the Early Macintosh Floppy Drive
#10Earlier quoted context omitted.
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.
> 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.
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.