Re: Infocom V4+ nibble format (was Re: 80 Cols. In Apple II Infocom Games)

[russotto@grace.speakeasy.net (Matthew Russotto)]

In article <4512f3f2$0$18495$9b4e6d93@newsspool3.arcor-online.net>,
Linards Ticmanis  <ticmanis@gmx.de> wrote:
>Hello,
>
>Speaking of the Infocom games, I wonder if anybody has already
>deciphered the nibble format that they used on the back side of the disk
>for the Apple versions of their V4 and later games.
>
>It's obviously a "one giant sector per track" format, not for copy
>protection (which Infocom generally did in the form of package contents
>that were needed to solve the game), but for getting more bytes onto
>that disk surface.

Once you know that, you pretty much know it all, except for the
interleave.  Each track has 18 data fields (including the d5/aa/ad
and de/aa/eb).  I believe they are uninterleaved, but I'm not sure.  I
think there's already a program on the IF-archive to read them off a
.nib image; I know I wrote one at one point, which may or may not be
the one in the archive.