fischer-michael@YALE.ARPA.UUCP (07/07/87)
I wrote a little program to display the FAT (File Allocation Table) on a disk that appeared to be completely full and was surprised to see the last two clusters (= 4 sectors) free. Looking at the data itself confirmed that they were unused. Doing a little arithmetic, I came up with the following: When formatting a SS disk, TOS announces 357376 bytes free. Floppy disk space is allocated in clusters of 2 sectors = 1024 bytes, so 357376 bytes = 349 clusters = 698 sectors. Add to that 1 for the boot sector, 5 for each of the 2 copies of the FAT, and 7 for the root directory, and you get a total of 716 sectors. A standard format disk has 80 tracks times 9 sectors per track for a total of 720 sectors, so indeed there is a discrepency of 4. Similar results apply to a DS disk: TOS announces 726016 bytes free = 709 clusters = 1418 sectors. Add to it the 18 sectors at the beginning to get 1436 sectors, 4 less that the 1440 on a raw disk. Has anybody else noticed this before? Is it a TOS bug? If so, has it been fixed in the newer ROMs? --Mike Fischer <fischer@yale.arpa> -------
dragon@oliveb.UUCP (Give me a quarter or I'll touch you) (07/08/87)
in article <8707071803.AA02575@yale-eli.arpa>, fischer-michael@YALE.ARPA (Michael Fischer) says: > I wrote a little program to display the FAT (File Allocation Table) > on a disk that appeared to be completely full and was surprised > to see the last two clusters (= 4 sectors) free. Looking at the > data itself confirmed that they were unused. Doing a little > ... > Has anybody else noticed this before? Is it a TOS bug? If so, > has it been fixed in the newer ROMs? > > --Mike Fischer <fischer@yale.arpa> I've sort of noticed this, in the sense that when a disk is formatted under MS-DOS it gives more space available (~361,000 bytes) than a TOS disk which is 'supposedly' formatted in a compatible way. Now why this is done, I don't know, but imagine it would be explained in the Abacus book about ST drives and disks. Anyone else have a clue? -- Dean Brunette {ucbvax,etc.}!hplabs!oliveb!olivej!dragon Olivetti Advanced Technology Center _____ _____ __|__ _____ 20300 Stevens Creek Blvd. | | _____| | | Cupertino, CA 95014 |_____| |_____| |__ |_____
dclemans@mntgfx.MENTOR.COM (Dave Clemans) (07/09/87)
From what I've understood, the two missing sectors in GEMDOS disk partitions are a result of a mistake made by whoever at Digital Research implemented GEMDOS. MS-DOS reserves the first two entries in the FAT, as does GEMDOS. However, MS-DOS adjusts the FAT table size to account for the reserved entries (i.e. increases its size by two). GEMDOS doesn't do this; thus the last two clusters get lost. dgc