Defining Disk Image Dump Standard

From: Eric Smith <eric_at_brouhaha.com>
Date: Wed May 31 16:57:38 2000

Sellam wrote:

> Broderbund came out with an 18-sector format for the Apple ][, but in
> order for the disk to be readble the first track is encoded as standard
> 16-sector format.
>
> This 18-sector format provided two benefits: 1) increased storage space
> and 2) a form of copy protection.

On some later Infocom titles for the Apple ][ family, they went to two
disk sides, and in order to maximize the amount of data on the second
size (and hence minimize flipping), they went to *one* sector per track.
This does away with the "wasted space" of intersector gaps.

Where they screwed up, though, was in sticking to a single byte of XOR
checksum over the entire "sector". The checksum scheme Apple used was
arguably inadequate for 256-byte sectors; it was truly horrible for
>5.5 Kbyte sectors.
Received on Wed May 31 2000 - 16:57:38 BST