Re: Question about writing to 1541

From: Nicolas Welte (
Date: 2005-05-06 09:42:01

Hi Spiro,

Spiro Trikaliotis wrote:
> OTOH, the 4040 used a gap between the data block header and the data
> block itself of 10 bytes. The 2031 and 1540 (and 1541 up to $E000-ROM
> version -02) used 8 bytes, while the 1541 (-03, -05 and later) and 157x
> use 9 byte. I believe 8 bytes are critical if a disk is to be
> interchanged between a 154x and a 4040, as there might be "double SYNC
> marks", making the data block unreadable. With 9 byte, it is much more
> unlikely that this happens than with 8 byte.

This is very interesting! Did you actually disassemble all the format and 
block write routine versions to gain above values? good work!

What about the sync length of different ROM versions? Are they the same or do 
they also differ?

Interpreting your result, the disks can be damaged when you write to a disk 
that has been formatted on a short-gap drive with a long-gap drive, because 
the drive would not overwrite the old sync completely, but start rewriting it 
too late, because it waits for more gap bytes. Is that correct?

Hmm, now I'm curious what the 2040 does, with the extra sector on tracks 
18-24 (670 blocks free).


-> My Commodore hardware projects and the X1541 Shop at <-

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