Mental Blocks game diskette both IBM and C64 format on same side of disk

[Fort Apocalypse]

Meant to post this yesterday when it got slashdotted (sorry! I'm slow):

http://games.slashdot.org/article.pl?sid=08/09/29/157232

 

Article here:

http://trixter.wordpress.com/2008/09/28/th...-trixters-mind/

 

Description of how game "Mental Blocks" by Avantage (Accolade’s budget publishing title) was custom formatted so that it would work for both C64 and IBM on the same side of the diskette!

 

Here is the section of the article by Trixter that you might find interesting:

...until I looked at the FAT12 for the disk and saw that tons of sectors in an interleaved pattern were marked as BAD — very strange usage.

 

A DIR on the disk shows that only about 256K of it is usable as space, instead of 360K. My Central Point Option Board’s Track Editor (TE.EXE) confirmed that every other track on side 0 cannot be identified as MFM data. So the manual is correct, and this truly is a mixed-format, mixed-architecture, mixed-sided diskette.

 

This diskette has officially blown my mind.

 

This is the very first time I have ever seen something like this. The data for the IBM program takes up more than 160KB as evidenced by a DIR. The C64 1541 drive is a single-sided drive; IBM’s is double-sided. Based on all this, we can deduce how this diskette is structured and why:

 

- The IBM version of the game required more than 160KB (ie. needed more than one side of a disk), probably because it has a set of files for CGA/Herc (4/2 colors) and another for EGA/Tandy (16 colors) and either set will fit in 160K but both won’t

- The C64 version required around 80K, based on the fact that every other track is unreadable by an IBM drive

- The publisher had the requirement of using only a single disk to save on packaging and media costs

- Not wanting to limit the game to either CGA or EGA, someone at Artech (the developer) built the format of this diskette BY HAND so that DOS would not step on the C64 tracks, and somehow the C64 would also read/boot the disk

 

I don’t know how the C64 portion boots since track 0 sector 0 looks like a DOS boot sector, but quick research shows that C64 disks keep their index on track 18. If anyone knows how C64 disks are read and boot, I’d love to know.

...

 

(note: if you can help him, please reply on that page in addition to this one)

[crunchysuperman]

I seem to recall some floppies like this from way back when. Pretty neat trick really, but then the inefficiency of the 1541's head made lots of crazy nonsense possible.

 

Inside Commodore DOS was the bible for Commodore users back in the day, maybe that'll help him. There's an online copy here.

[crunchysuperman]

double post

Edited October 1, 2008 by crunchysuperman