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When powered on 1541 reads the disk for a brief moment. Is it used to boot system from floppy? Is it possible to create a bootable commodore 64 floppy?

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On the C64, no.

On power up, the drive is resetting and the motor may spin briefly, but the drive is not actually reading the disk.

And even if it were, it is an IEC slave device and cannot initiate communication with the C64/C128 bus master itself.

For an auto boot concept to be implemented, it would have to be the computer's kernal directing the flow of events, on reset.

While theoretically possible to implement, no such option exists on stock C64 machines.

However, the C128 actually implements this concept and at reset checks the sector 0 of track 1 for a special signature boot sector.

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  • I wonder why the C128 looked at T1S0 rather than trying to load a file with a particular name? The latter would have failed faster in the absence of a disk in the drive.
    – supercat
    Commented Sep 19, 2020 at 18:46
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    @supercat Other than the boot sector concept probably being inspired by other systems that did it like that, the PRG gives a hint of the rationale by stating that "The loading of sequential sectors [from the boot sector] is designed primarily for special applications (such as CP/M or games) that do not need a disk directory entry" [p.447].
    – user6576
    Commented Sep 19, 2020 at 20:09
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    Note that there is also a basic command (BOOT) on the C128 [PRG, p.29], to boot off a bootable disk, without resetting the computer. So you could put in a disk, and then launch it.
    – user6576
    Commented Sep 19, 2020 at 20:21
  • Its probably worth adding that the C128 autoboot function works with almost all Commodore drives and many 3rd party compatible ones (including all CMD disk and HDD drives) as well.
    – mnem
    Commented Sep 19, 2020 at 21:31
  • @Retrograde: If the magic name were longer than 16 bytes, then drives that understand it (like the 1571 could be programmed to do) could treat it as a cue to seek to the first track, check whether a disk is present, and if so start retrieving data sequentially, while existing drives like the 1541 would simply use the first 16 bytes. That would make it possible to have a bootable CP/M disk without having to reserve track 18.
    – supercat
    Commented Sep 20, 2020 at 17:30

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