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ADAM Nonstandard Disks - Interleave Values


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Greetings programs!


From Marcel's ancient but incredibly useful site, I came across this information on disk sizes utilized by the ADAM (with 160K being the 'coleco standard' size):

image.png.7441002d8257082626be46973b4d34cf.png

 

I can confirm that 160K and 320K work just as described with a sector interleave of 5. That is, the sectors on a track are laid out in the following order:

00  05  02  07  04  01  06  03

 

And the 720K parameters also make sense with a sector interleave of 4 (given 9 sectors/track):

00  04  08  03  07  02  06  01  05

 

But the 1.44M (and 640K which I don't care much about) seems wrong. With 18 sectors/track, the interleave of 4 doesn't make sense to me. Maybe the first 9 sectors of a track and last 9 sectors of a track are both 'Interleave 4' but I don't see how 18 sectors could be 'Interleave 4' as the modulo math doesn't work out.

 

Interestingly enough, an Interleave of 5 still works out for the 1.44M parameters:

 

00  05  10  15  02  07  12  17  04  09  14  01  06  11  16  03  08  13

 

Anyone have any insights on how a 1.44M disk was laid out for Adam use?

 

 

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11 hours ago, wavemotion said:

Anyone have any insights on how a 1.44M disk was laid out for Adam use?

Greeting programmer!

 

Since Marcel hasn't been involved in a LONG time, your next best option to find any pertinent info would be the tech files that Micro Innovations shared with the community and most include source code. Here's a direct link to the proper directory on The ADAM Archive:

 

(AdamArchive.Org) - The home for everything ADAM

 

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Boom! Thanks, Jim. That was exactly what I needed - the firmware is well commented and the skew factor is, indeed 4:1 but they SKIP from 15-->2 (5:1) to get the sectors back on track (no pun intended).

 

image.thumb.png.70e85360eec451402ed9e82461dee3d5.png

(note: sectors here are one-based:  1-18)

 

Soft sectored disks can be laid out in any manner - including just a linear layout (1,2,3... etc). The skew is simply used to help efficiency since while the computer is processing the sector just read, other sectors will fly by under the disk read head and having a skew means that when the computer asks for the next logical sector it's more likely to have that sector "coming up" rather than wait for a full rotation of the disk to get that sector back under the head.

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