Defining Disk Image Dump Standard

From: Sellam Ismail <>
Date: Thu Jun 1 12:35:39 2000

On Wed, 31 May 2000, Sellam Ismail wrote:

> Track Descriptor Header
> 1. Track number (2 bytes: 1 for whole number, 1 for fraction) [1]
> 1. Track format (logical or raw; host computer specific) (1 byte) [2]
> 2. Track size in bytes (2 bytes) [3]
> 3. Sector format (single-density, double-density, etc) (1 byte)

Insert "Sector Interleave" (will 1 byte suffice = 2 4-bit values?)

> 4. Sectors in this track (1 byte)
> 5. Bytes per sector (2 bytes)
> 6. Bits per byte (1 byte)
> 7. Offset to next Track Descriptor Header (2 bytes)

Special raw disk bytes such as synchronization bytes (as on the Apple ][)
will have to be denoted in some fashion. But how?

There were anywhere from 8 to 16 8-bit sync bytes (having the value 255)
found at the beginning of each track and before each sector that contained
two additional zero bits at the end (so they looked like 1111111100).

How will these get stored? Perhaps a map could be included with raw track
data to specify sync bytes. The map would be a series of bits, each bit
corresponding to a byte in the raw track image, a 1 bit meaning the byte
is a sync byte and a 0 meaning normal. The bits can be packed into bytes
so that a track of 5,472 bytes (roughly the theoretical size of a raw
16-sector Apple ][ disk track) would take 684 additional bytes.

Sellam International Man of Intrigue and Danger
Looking for a six in a pile of nines...

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Received on Thu Jun 01 2000 - 12:35:39 BST

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