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Emulating the Early Macintosh Floppy Drive

thomasw.dev

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Re: Emulating the Early Macintosh Floppy Drive

#21

Post by brudgers »

chuckadams wrote: post #12
wtallis wrote: post #10

Earlier quoted context omitted.

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 fl…

Right, I forgot about flopticals… but I guess almost everyone else did too. NeXT boxes had those, didn’t they?

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.

Re: Emulating the Early Macintosh Floppy Drive

#22

Post by memcg »

hnpolicestate wrote: post #9

Got myself 3 iMacs (1998) and 2 Macintosh SE's (not sure specific model yet) yesterday at an estate sale for $50.

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.

Re: Emulating the Early Macintosh Floppy Drive

#23

Post by userbinator »

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.

Re: Emulating the Early Macintosh Floppy Drive

#24

Post by camhenlin »

userbinator wrote: post #23

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.

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.

Re: Emulating the Early Macintosh Floppy Drive

#25

Post by wmf »

userbinator wrote: post #23

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.

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.

Re: Emulating the Early Macintosh Floppy Drive

#27

Post by ForOldHack »

Lammy wrote: post #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. Pard…

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.

Re: Emulating the Early Macintosh Floppy Drive

#28

Post by ForOldHack »

thought_alarm wrote: post #7
tom_ wrote: post #3

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…

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 A…

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.

Re: Emulating the Early Macintosh Floppy Drive

#29

Post by ForOldHack »

wazoox wrote: post #17
chuckadams wrote: post #12

Earlier quoted context omitted.

Right, I forgot about flopticals… but I guess almost everyone else did too. NeXT boxes had those, didn’t they?

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.

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.
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