Lisa's scores

[...] What did they do in that filesystem? I am curious because the PERQ, which was another machine that came from the Xerox PARC work also had a very interesting filesystem under POS (the first OS that was written for it). In particular : Files are linked lists of blocks. The sector header of each sector on the hard disk contains pointers to the previous and next blocks in the file, along with some other info that I've forgotten Files may be sparse - the fact that block n exists does not mean that block n-1 does Block 0 of each file (I think, maybe block -1) contains the 'file descriptor' - bascially an i-node. Negative block numbers are the file allocation map. You can use this to quickly find any block in the file without following the links. Directories are sparse files. When you access a file in a directory, the filename is hashed in some way (the algorithm is not in the manual), and the hash value is used as the first directory block to look in. If the 'file descriptor' gets mangled it can be recreated from the header pointers. If the header pointers get mangled they can be recreated from the file descriptor. Ditto about other important structures on the disk - loss of any single one is generally recoverable using standard utilities. Were any of those things done on the Lisa? -- -tony ard12(a)eng.cam.ac.uk The gates in my computer are AND,OR and NOT, not Bill