Evening John, Thanks for yet more explaining. I discovered (!) that if I take the file_id from the file's entry in the directory and use that to index into the block map (having subtracted 1 first) I get a 'value' which I call stragely, the block number.
Multiply that by the number of sectors per disc and we have a sector number. Multiply that by 512 and we have the file's address in the hard disc. It appears that in QLWA formatted 'discs' there is a header of 64 bytes at that address immediately followed by the first 2048-64 bytes of the file. Progress! I haven't yet figured out where the second block of the file should be, but I'll be looking at some point in the future.e I thought that the block number (also) pointed at the next block in the chain but when I followed that logic, I found that the second block in my test file was not in anyway connected to the first one. Needs more investigation I think. > Almost :-) > The chain actually belongs to the header/map and map entry $F > (containing $0000) is the last in the chain. Hmmm, see above. This is where I seem to lose the plot. Are you saying that the zero block in the map, holding $0001 is telling me (a) where on disc to find the 4 sectors for this block PLUS (b) where the second block in this file is (ie, map entry $0001). This is what I tried with my test file but got nowhere. :-( >> Unless you >> mean block $338f and not block zero of course, as the first free >> block. > > Yes: > > map_entry_for_first_free_group->map_entry_for_next_free_group->... Ok, thanks. > That's right - the file number is an index into the directory, not the > map or the disk. I was going to ask about sub-directories and adding/deleting files to and from those but then I discovered that each entry in every directory has a file_id word (implies 65536 maximum files per disc) at offset $3a in the directory entry - which leads nicely into the block map and from there to the first 4 sectors on disc. >> last question for now. Where did you find out? > I could tell you but then I'd have to kill you :-) Aha, that old one - I use it often myself at work. :-) > Actually, the scheme is basically the same as used by FAT-formatted PC > disks. Ok, thanks, I'll see what other info I can dig up on FAT discs sometime. Might help! > The rest is just experience and a (little) bit of logic... Ah well, experience is something I can look forward to, I only started this yesterday! Thanks again. Cheers, Norman. _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
