Re: format difference between a 4040 and a 1541

On Sun, Sep 28, 2025 at 6:48 PM Spiro Trikaliotis
<ml-cbmhackers_at_trikaliotis.net> wrote:
>
> Hello,
>
> just to add a little bit to Andrés statements:
>
> * On Sun, Sep 28, 2025 at 02:44:10PM +0200 André Fachat wrote:
>
> > The dual CPU drives write 8 byte of real gap data bytes, which get translated
> > into 10 GCR bytes.

if the conversion program I'm using is doing its job, on a freshly
formatted header, even the 4040 has 9 bytes of gap (gcr encoded).

4040 raw header:
; Following raw bytes:  52 57 d5 55 72 9a a6 a5 29 4a 52 94 a5 29 4a 52 94 a5
 2b

1541-05 raw header:
 ; Following raw bytes:  52 57 95 79 72 9a e6 e5 55 55 55 55 55 55 55 55 55 55
 55 ff

(the ff should be the sector sync start)

On the other hand, when a sector has been re-written after the initial
formatting, there're differences:

4040:
; Following raw bytes:  52 57 25 29 72 9a a6 a5 29 4a 52 94 a5 29 4a 52 94 a5
 10 de ff

1541-05:
 ; Following raw bytes:  52 57 75 29 72 9a e6 e5 55 55 55 55 55 55 55 55 55 55
 52 bf

It seems the 4040 waits one byte too much before starting to write the
data part of a sector and "spoils" the start of the data sync. On the
other hand the 1541-05 delay is consistent with the length of the gap
used at format time.
If I understand correctly what's going on of course.

Best regards
Frank IZ8DWF