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The Apple Disk II Controller Card (2021)

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Re: The Apple Disk II Controller Card (2021)

#11

Post by RachelF »

TMWNN wrote: post #5
dboreham wrote: post #4

Earlier quoted context omitted.

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

>Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. I disagree that the approaches are similar. The 4040 https://en.wikipedia.org/wiki/Commodore_4040 > is a monstrosity; even the later single-drive models, such as the 1541, are massive. Apple's 1978 floppy drive +…

Yes, at the time the Commodore drive was jokingly referred to as "the Cadillac of disk drives" - long and slow.

Re: The Apple Disk II Controller Card (2021)

#12

Post by cameldrv »

dboreham wrote: post #4
TMWNN wrote: post #3

As zellyn said, Disk II is pure genius writ large. It's flabbergasting how good Woz's designs were. Almost on a whim, he with the Disk II did something no one anywhere in Silicon Valley—anywhere in the world —was doing. Forget about IBM, HP, Shugart, Tandon. Just within Commodore and Tandy, Apple's direct 1977 competitors, there were abundant human and engineering resources to come up with a fast, inexpensive, and re…

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

They were really slow though. It took minutes to boot up a game from the 1541. I never had one but my friends did, and one of them had a "Fast Load Cartridge", which I believe just replaced the software on the drive and on the computer with better software that was something like 5x as fast.

Re: The Apple Disk II Controller Card (2021)

#14

Post by ajross »

dboreham wrote: post #4
TMWNN wrote: post #3

As zellyn said, Disk II is pure genius writ large. It's flabbergasting how good Woz's designs were. Almost on a whim, he with the Disk II did something no one anywhere in Silicon Valley—anywhere in the world —was doing. Forget about IBM, HP, Shugart, Tandon. Just within Commodore and Tandy, Apple's direct 1977 competitors, there were abundant human and engineering resources to come up with a fast, inexpensive, and re…

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

That's very much missing the point. It's absolutely true that the "approach" was similar (the bit encoding was software-generated in a timing loop and fed to non-ASIC hardware to send to the drive).

But the Disk II card was 8 chips you could get from Radio Shack, where the 8050 was a monster with a whole CPU/memory/bus (you can see the board appear in this video at 1:15 https://www.youtube.com/watch?v=S3d2cNSAB9A&t=69s).

And Woz's was faster. And hit market almost two years earlier. There's an aesthetic judgement to be made here too, and... it's not remotely close.

Re: The Apple Disk II Controller Card (2021)

#15

Post by II2II »

TMWNN wrote: post #5
dboreham wrote: post #4

Earlier quoted context omitted.

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

>Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. I disagree that the approaches are similar. The 4040 https://en.wikipedia.org/wiki/Commodore_4040 > is a monstrosity; even the later single-drive models, such as the 1541, are massive. Apple's 1978 floppy drive +…

We need to be careful with our comparisons here.

Even though the Disk ][ was significantly faster than the 4040, the 4040 was significantly faster than the 1541. Apparently the difference was largely due to a bug in the controller used for the Commodore serial bus.

Commodore's 8-bit micros also used IEEE-488 (or a serialized form of IEEE-488) for their floppy drives, rather than a dedicated expansion card that was connected to a bus with direct access to the CPU and RAM. While the expansion bus on the Apple II was fast enough to control the drive directly, the most Commodore could do was send and receive a stream of data to the drive. The drive had to have the smarts to interpret that stream of data. The drive electronics was going to be more complex than Apple's even if Commodore assigned amazing engineers to the task.

Finally, Commodore's approach had its own advantages. Since the drive accepted and handled commands, the CPU could be freed up for other tasks. I don't know how useful that was in general, but the classic example involved two drives autonomously copying floppies. (You could literally remove the cable between the computer and the drives after the operation was setup.) I also recall hearing about classroom setups where multiple computers would share a drive (PET era). It also allowed more drives to be connected to the same bus. Apparently 8 drives were supported. In contrast, the Apple II would support two drives per expansion slot.

Re: The Apple Disk II Controller Card (2021)

#16

Post by TMWNN »

cameldrv wrote: post #12
dboreham wrote: post #4

Earlier quoted context omitted.

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

They were really slow though. It took minutes to boot up a game from the 1541. I never had one but my friends did, and one of them had a "Fast Load Cartridge", which I believe just replaced the software on the drive and on the computer with better software that was something like 5x as fast.

>that was something like 5x as fast.

... which is still significantly slower than the Disk II.

The 1978 Disk II is about 30 times faster than the unaccelerated 1982 Commodore 1540/1541, as well as more reliable,[1] cooler-running,[2] and just more elegantly designed. The same comparison holds for the 4040 and other pre-1541 Commodore drives, albeit with the speed disadvantage vis-a-vis Apple being less.[3]

[1] The 1541's drive head often goes out alignment despite both it and Disk II using similar "ratatatat" methods to return to the first track. Also, the first couple of years of 1541 production were notorious for failures in general.

[2] As the 1541 is a standalone 6502-based computer with an integrated power supply, overheating is constantly an issue.

[3] Yes, the 1541 is slower than earlier Commodore drives, because of the move from parallel to serial IEEE-488 and a hardware bug (that both necessitated and allows for Fast Load and its counterparts)

Re: The Apple Disk II Controller Card (2021)

#18

Post by musicale »

I just have to say when I saw BMOW 1 I was delighted.

Also Magic-1, another homebrew CPU, also made out of 74LS TTL chips from the 1970s.

Fantastic trend, really.

https://www.bigmessowires.com/bmow1/

https://homebrewcpu.com

(Of course it's a lot easier [but still quite fun] to make your own homebrew CPU/system on an FPGA.)

Re: The Apple Disk II Controller Card (2021)

#19

Post by gblargg »

Great read. The section about copy protection and being able to step the head motor half tracks and do things like store tracks at half positions, or even store 180 degrees at one position and another for the rest, was very interesting. The disk copiers at the time always seemed pretty sophisticated, but I didn't realize they had to deal with things like this. I bet those were fun to write (and be part of the arms race).

Re: The Apple Disk II Controller Card (2021)

#20

Post by dezgeg »

cameldrv wrote: post #12
dboreham wrote: post #4

Earlier quoted context omitted.

Commodore disk drives (4040 and so on) actually use a very similar approach. There's no FDC controller chip and the 6502 is hooked to the drive (literally the same SA-390 as Apple used) via simple hardware. The only significant difference is that the 6502 (actually two of them) is in a separate enclosure from the Pet , communicating via IEEE-488. Since Commodore manufactured the 6502 presumably it was ok to use them…

They were really slow though. It took minutes to boot up a game from the 1541. I never had one but my friends did, and one of them had a "Fast Load Cartridge", which I believe just replaced the software on the drive and on the computer with better software that was something like 5x as fast.

The bottleneck was with the serial protocol between the drive and C64. It was done via bit banging in software due to some chip bug. The fastloaders replaced the protocol with something more amenable to bitbanging.
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