John Hall writes: > Hi, Norman. > >>> 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). > > Hmm... the map chain is, perhaps, a bad example because it is not > actually associated with a file. > > Consider the root directory: > > The medium header tells us that its first group number is $10, i.e. > its first 4 sectors are sectors $40, $41, $42, $43 on the disk. > > If the $10-th entry in the map is zero, the directory is contained > within those 4 sectors. > > If not, the map entry tells us its next group number, i.e. where its > next 4 sectors are. > > For your disk, the $10-th map entry is $5c, so the 5th sector is > sector $170 (since $5c*4 = $170) and the 8th sector is sector $173. > > If the directory is more than eight sectors in length, the $5c-th > entry will be non-zero, and so on... > > For all other files, the first group number is, as you say, stored in > the directory entry (offset $3a) for that file.
Good stuff all this. I hope someone's taking notes! It would be nice to have this information in a neat documentary form. Luckily, this seems to be what Norman (condolences!)is trying to do with his well-made and useful QDOSMSQ.Dunbar-it.co.uk site. Thanks guys! Per _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
