This is the video recording of “The Ultimate Commodore 1541 Disk Drive Talk” at VCF West 2021. As always, if you think it’s too fast, try watching it at 0.75x speed!
I will post the slides in Apple Keynote format later.
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12 thoughts on “The Ultimate Commodore 1541 Disk Drive Talk [video]”
Did you explain how file write protection works? You know the `PRG<`.
That's a filesystem feature, right?
I did not. But it’s easy. Bit #6 of the file type is the write-protect (lock) bit, so just OR the type with $40 to protect it. $83 is PRG, so $C3 is write-protected PRG. The 1541 doesn’t have a DOS command to protect/unprotect, some later drives support it.
Are you familiar with the copy protection on Chess Master 2100? I have always wondered how it worked. There were just a small file that started up the game.
Great video about 1541!
Any news about Commodore Peripheral Bus series?
Part 6: JiffyDOS  (coming soon)
Part 7: Fast Serial [C128; 1986] (coming soon)
Part 8: CBDOS [C65; 1991] (coming soon)
Really interested about C128 fast serial.
There was also the earlier 1540 drive, which came with the VIC-20. It had a faster data transfer because the VIC-20 didn’t have the C-64’s extra 40µs video gaps as explained in the video, but it was too fast for the C-64. It could later be converted into a 1541 by exchanging the operating system on the EPROM.
Lots of great info that I had no memory of any more, including all the improvements made to the transmission and formats after my initial discoveries.
Since Apple’s drives were mentioned, here’s another interesting detail: Apple didn’t change the encoding density on the various tracks in 4 groups as it was done on the Commodore drives but instead had different spinning speeds depending on the track number, and in a more gradual form, IIRC. This made it impossible to read/write Apple II floppys on a Commodore drive.
are you sure that the Apple disk II drives have variable speed?
Afaik they are fixed speed while the Macintosh DD format drives uses variable speed.
A source claiming fixed 300 RPM speed:
Apple used Shugart SA-400 drives running at a fixed 300 rpm. However, they used their own amplifier board, which was much cheaper than the original board.
The fixed speed is the reason why an Apple Disk ][ has a capacity of 143 kB, while the 1541 stores 170 kB per disk area.
So I been using 1571 with Zoom Floppy to convert all my disk to NIB and latter to G64….Any specific setting for nibtools to read specific protection or best default settings?
Ok I just watched this video for the first time, and it was incredible. I was intending it being some background listening while I was working on other things and just found myself watching. The depth was perfect, and I did not find the delivery to be too fast at all.
Please do more!
Thank you very much for this incredible talk. It was very inspirational, so I decide to digitize ROM comments from “Inside Commodore DOS” book: https://g3sl.github.io/c1541rom.html I hope it will be useful.