ATR Header?

[+Larry]

Here is info from Nick Kennedy's SIO2PC docs about the ATR header:

 

"WORD = special code* indicating this is an Atari disk file

WORD = size of this disk image, in paragraphs (size/16)

WORD = sector size. (128 or 256) bytes/sector

WORD = high part of size, in paragraphs (added by REV 3.00)"

 

I am not familiar with "paragraphs". If I try to use the typical (low byte + high byte x 256) /16 then I end up with 718.5. (?)

 

Does anyone know how to correctly decipher these "size" numbers (including the "extra" word added by "REV 3.00") ?

 

Thanks,

Larry

[drac030]

The size is counted in "16 byte increments", aka paragraphs. For example, 256 bytes = 16 paragraphs. 1024 paragraphs = 16x1024 = 16384 bytes.

Edited June 24, 2011 by drac030

[+Larry]

Thanks for the paragraph information, Konrad.

 

I think that I've also determined why the "size" doesn't come up to 720 (with my calculation) -- it would be off by exactly the 3 "single density" boot sectors.

 

If I nail this down, I'll re-post. Google referenced several related posts in the past, but I saw none that really answered my query.

 

Edit:

Yes, that's it! A SD disk/image should contain 720 * 128 = 92160 bytes.

a 90K ATR header shows a "word" value of 128, 22

That would be 22*256 + 128 = 5760 "paragraphs"

5760 * 16 = 92160 bytes.

Thanks, again!

 

-Larry

 

 

The size is counted in "16 byte increments", aka paragraphs. For example, 256 bytes = 16 paragraphs. 1024 paragraphs = 16x1024 = 16384 bytes.

[+CharlieChaplin]

Hello Larry,

 

do you still use version 3.00 of SIO2PC ?? Remember, this version has a bug, it produces enhanced density ATR`s with a length of 140kbytes (143,xxx Bytes), so better use a newer version like 4.1x or 4.2x. If you try to copy/download such a 140k ATR with a Sectorcopy program, most of the time the copy program will recognize it as SD/90k, so you have problem there... (which I solved with MyCopier 1.c and setting the "E"nhanced density switch to "on")...

 

-Andreas Koch.

Edited June 25, 2011 by CharlieChaplin

[+Larry]

Hi Andreas-

 

Thanks, but I don't use SIO2PC -- just Win APE. However Nick's SIO2PC docs explain the header slightly better than Steve Tucker's Disk Image FAQ's, so I quoted from Nick (verbatim). I don't think that I'd ever heard of the "paragraph" term before.

 

-Larry

 

Hello Larry,

 

do you still use version 3.00 of SIO2PC ?? Remember, this version has a bug, it produces enhanced density ATR`s with a length of 140kbytes (143,xxx Bytes), so better use a newer version like 4.1x or 4.2x. If you try to copy/download such a 140k ATR with a Sectorcopy program, most of the time the copy program will recognize it as SD/90k, so you have problem there... (which I solved with MyCopier 1.c and setting the "E"nhanced density switch to "on")...

 

-Andreas Koch.

[Chilly Willy]

A 180K double-density disk is off by three sectors of 128 bytes because the first three sectors are ALWAYS 128 bytes, even in double-density. This is because the disk boot process loads three sectors assumed to be 128 bytes each. Double-density disks store the data as 256 bytes sectors, but the control board only returns half the sector data for the first three sectors.