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intric8
Seattle, WA, USA
Website

Posted Mon Jul 13, 2020 11:21 am

4-minute video on the Cadillac of Commodore 8-bit floppy disk drives: the 1581.


The Commodore 1581 is a 3-and-a-half inch (3.5”) floppy disk drive that debuted in 1987 for Commodore 64 and 128 computers. It was even compatible with the Plus 4, Commodore 16 and VIC-20. Can you imagine using the 1581 with a VIC? It would have been insane!
1581-amigalove.jpg
Photo © Amigalove, Attribution 3.0 Unported (CC BY 3.0)


The 1581 uses double-sided double-density disks formatted in a Modified Frequency Modulation scheme, or MFM, which could also be used with CP/M, IBM compatible PCs and Amigas. These disks can store up to 800 kilobytes of data, 400 per side. The 1581 was the highest capacity serial-bus floppy drive ever produced by Commodore for its 8-bit line, although CMD (Creative Micro Designs) would later surpass it in the early 1990s.
IMG_7836.jpg
Photo © Amigalove, Attribution 3.0 Unported (CC BY 3.0)


As a comparison, a single side of a Commodore 64 5-and-a-quarter floppy disk could hold approximately 170 kilobytes (so a little over 300 KB per disk if you notch a disk, flip it and use both sides). Therefore, a Commodore 1581 disk can hold more than twice a double-sided 5.25” “flippy disk”, and over 4 times a single-sided 5.25” floppy. 
With special software and under the right conditions, it is even possible for the 1581 to read MS-DOS disks. And even cooler, the Amiga can read 1581 disks, too.
IMG_E8399.JPG
Photo © Amigalove, Attribution 3.0 Unported (CC BY 3.0)


The 1581 also supports the C128’s burst commands - commands used for machine language programs - that transfer data several times faster than the standard or fast serial rates. (Sorry Commodore 64s, no bursting for you!). It can automatically adjust its speed to the computer it is connected to, Compared to a 1541, the 1581 has about 20% faster loads and about 45% faster saves. Add JiffyDOS to the mix and it might feel like it is hitting Warp 9.

The 1581 also has support for sub-partitions and directories, which helped make it become an archivist’s dream, not to mention Bulletin Board sysops needing a lot more space at the ready.

However, unlike the 1571, which is nearly 100% backwards-compatible, the 1581 is only compatible with previous Commodore drives at the DOS level. It can’t utilize software that performs low-level disk access, which the majority of C64 games do. To be honest, this major flaw is really the only knock against it. But from a pure storage perspective, the 1581 was, and is, a great piece of period-correct hardware.

At the end of the day, the 1581 is one of the quietest, fastest, smallest and sexiest drives Commodore ever made for the C64 and C128. And it deserves the highly regarded status it has earned over these past 30+ years.

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Zippy Zapp
CA, USA

Posted Mon Jul 13, 2020 9:08 pm

Awesome write up and video, intric8. This for me was one of my favorite drives back then. I also bought mine from Toys R Us around the time it came out. I think it was $299 for me though, although I don't still have the receipt, but thankfully I kept it in its original box with all papers and have the original test/demo disk. I can't believe what they are going for now.

One thing to note though is that some early drives had a problem and may have needed a new controller chip, IIRC. It led to corrupt directories and some other oddities. I don't know if they fixed it with a ROM patch or a different WD chip. Mine is an early unit and I seem to remember a utility that was made that could identify if your drive had the problem. I never got mine fixed but it worked for my uses.

I do know that mine occasionally locks up when reading the directory but not always and not in every software package that uses it. I used mine mainly as a download section for my BBS which was awesome at the time. There is a command you can enter that fixes the lockup bug and prevents it from happening. I think my BBS software did this at bootup. I seem to recall it is in the Action Replay 5 docs too.

On the software front there was a few applications that took advantage of it. Many of the later fast loader carts supported it on 64. Maverick Copier supported it as did many utility programs including Quantum Link's own utility software. Also GEOS is great with a 1581. I also used it for storing many of the SID .MUS music files with accompanying Word (.WRD and Picture .PIC) files that were all the rage on Q- Link. I made game compilations too with disks filled with 1 file games and utilities.

LoadStar had published quite a few apps for 1581 use and they even started making LoadStar available on 1 3.5" disk instead of 2 5.25" disks. Ah well, sorry for rambling but you hit my nostalgia bone again.

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Bulletdust

Posted Tue Jul 14, 2020 2:57 am

Here in Australia, where the C64 had really dropped in popularity in favor of the Amiga by the time the 1581 was released, the drive itself fetches a fortune and is literally unobtainium.

That particular example is very clean Intric8.

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intric8
Seattle, WA, USA
Website

Posted Tue Jul 14, 2020 10:59 am

@Zippy Zapp
Thanks for the kind words. Glad you liked it!

If I were to install JiffyDOS into the 1581, wouldn't that eliminate the potential for all of the original bugginess? I think someone suggested as such to me.

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Zippy Zapp
CA, USA

Posted Tue Jul 14, 2020 6:58 pm

intric8 wrote:
Tue Jul 14, 2020 10:59 am
@Zippy Zapp
Thanks for the kind words. Glad you liked it!

If I were to install JiffyDOS into the 1581, wouldn't that eliminate the potential for all of the original bugginess? I think someone suggested as such to me.
I think it may fix some. But check this out, as it lists all the bugs and the causes and most importantly the name of the program to detect the bugs:





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