David_W_Tamkin@cup.portal.com (11/02/88)
If you have allocated sectors on a disk outside a file (typically the boot sector[s] of a disk intended to be used with a 128), validating the disk frees them again and leaves them vulnerable to overwriting. In the 1581 format one can protect them by partitioning them off. If one points a dummy file to a boot sector, its first two bytes provide an invalid link ($43, $42) and make the validation abort in midstream, making things even worse. I had the idea that perhaps relative files were validated by reading the list of blocks named in the side sectors as a more efficient way than going through all the links in the chain of data sectors. If one tampered with the side sector[s] to name the boot sectors instead, perhaps that would protect the boot sector[s] from being de-allocated during validation. Well, it didn't work. In validating a relative file, the 1571 goes down the chain of side sectors and the chain of data sectors. So did my MSD-2.