Jarek Adamski wrote: > > Dnia 00-03-18 Mac Buster pisze: > > > Its is possible to format track w/o any ID at all :) > Right, is possible on 1793 type FDC, but not on 765A vel 8272 > (the one used by IBM in its primitive computer).
This is possible and I know several copy-protection system on PC which uses such scheme. The main idea is very simple. You're formatting a track and write there standard IDs, next, you can used combination of "write track" and "force interrupt" to do a trick called "short format". > > But you can not read them back =) > Only with #E0 command in 1973 type FDC. Then you have to check > CRC, because the data can be inverted. Inverted ? Strange... I know sector data might be shifted on 1 or 2 bytes (called "time slice"), but inverted... > > But it is almost impossible to read disks with incorrect side > > marks, etc. > "Almost impossible" means it is possible, but not via INT 13h. "Almost impossible" means that it is possible to read it only on some machines - other machine may not read it. > I had recently the same problem with TOS A.2 disks. But finally > I made it without such special tricks. > It would be better to fix format code in Beta 128... This is dangerous. Almost all turbo-loaders use direct FDC programming and direct sub-routines addressing. If you change something in TRDOS rom then you may have "disk format" instead of "load program". Also TRDOS v5.xx in Beta 128 does not use complete track format and there are no special sector in beginning of each track. > [GCR] > That is what I meant. Any idea where to find GCR decoding description ? > > If you're working with standard disks only readed into . > I use 820kB disks with my SAM... ;) With 1kB sectors. :) > -- > Yarek.
