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PC Historian Finds Puzzling Game Diskette Image
This past weekend, Trixter — a self-proclaimed IBM PC historian — picked up some old software for his archive. What he didn't count on was a couple of additional Avantage titles that had never been released into the wild. If this weren't enough of a find, one of these titles provided Trixter with an interesting puzzle: the diskette for Mental Blocks is apparently hand-formatted to work on both C64 and IBM (on a single side, not the "flippy disks" of old). Quite an interesting little piece of history.
Wonder how many patents this potentially invalidates?
This does look like a very early example, but the technique is not as novel and amazing as the article makes out.
For example, in the UK around 1989 there was a magazine for Atari ST and Amiga users called "ST/Amiga Format" that used a hybrid format on 3.5" coverdisks. The ST used a PC-like 720MB format, whereas the Amiga had its own filesystem that fitted 880MB on the same disk. The hybrid disks weren't flippable, they were read double-sided on both systems and just marked the part of the disk used for the other filesystem as bad.
For some reason it reminds me of the floppy records that came inside magazines, when I was a kid. We would transfer the audio from the record to a cassette, then load the cassette into the computer.
Nobody even whispered, because we were convinced the least bit of sound would get mixed in and corrupted the whole thing. Same goes for acoustic-couple modems, except it really worked that way sometimes. Too much background noise and you'd lose carrier.
Ahhh.. the good old days.
Never ask for directions from a two-headed tourist! -Big Bird
That was the case for heavy-duty copy protection schemes. The idea was that you'd have a small area of the drive with a loader program in the "normal" format and track 18-0 as readable as well so you could do the directory, the rest in your own non-standard format the couldn't be read at all. You'd then do all sorts of wacky code tricks to obscute the loader program itself, but once it loaded, it could deal with the non-standard data blocks/tracks on the disk.
Ted
Actually, I butchered a few terms in my post most likely. My brain nearly froze trying to remember the different terminologies (block/sector etc) from back in the day! I haven't done low level disk stuff on any platform since the late 80's. I think I got the meaning across OK hopefully.
Also- I think the encoding was more likely at a lower level then even what you'd consider "track basis". I don't really know the IBM side so I don't know if the interleave would have been same, etc. Again I can visualize what I mean here, but I can't remember the terms anymore for what the "lead in", "gap" etc in the low level bit encoding was called. I think I've blocked out all the programming knowledge I used to have regarding getting the 1541 to do it's voodoo (*shudder*, assembly from hell!).
Ted
The "Macintosh-format" CDs don't use ISO, they actually use HFS/HFS+. The dual-format disks actually contain an ISO and an HFS partition, but they're engineered so that they share data. You can have ISO-only files, HFS-only files, and shared files; the shared files are only stored once. The ISO partition is used to store data for windows; the HFS partition is used to store data for Mac OS.
The interesting thing about those disks isn't that they're formatted to have two different filesystems on them -- by the time the dual-format CDs were around, putting two partitions on a disk was no big shocker. The interesting part was that they were designed to have two partitions own the same data.
Compare with the disk mentioned in the article. It sounds like the data for the IBM and C64 are entirely separate. The interesting feature is making what is essentially a two-partition disk out of a disk that's designed to be single-partition.