The first entry (cluster 0 in the FAT) holds the FAT ID since MS-DOS 1.20 and PC DOS 1.1 (allowed values 0xF0-0xFF with 0xF1-0xF7 reserved) in bits 7-0, which is also copied into the BPB of the boot sector, offset 0x015 since DOS 2.0. The first two entries in a FAT store special values: Reference: Wikipedia, Design of the FAT file system, Yes, it has been there since PC-DOS 1.0 at exactly this address! However, the byte only appears at address 0x015 in the BPB as of DOS 2.0. Here the so-called media descriptor appears again. Take a look at the very first byte in the second sector. The question now arises, how can DOS distinguish between single-sided and double-sided disks if there is no information in the BPB. The range 0x00B - 0x017 is completely empty no BPB!
The 9-sector format (SS & DS) was introduced with PC-DOS 2.0!įormatted as: 5,25", 160K, 48 tpi (SSDD), 8 sectors/track. The range 0x00B - 0x017 is „empty“ except for the string no BPB! PC-DOS 1.1īasically, PC-DOS 1.1 knows two disk formats: 160K, 48 tpi (SSDD), 8 sectors/track and 320K, 48 tpi (DSDD), 8 sectors/track. In the boot sector above, you will find two strings „7-May-81“ and the name Robert „Bob“ O'Rear. Furthermore, the standard signature 0xAA55 at the end of the boot sector is missing.įormatted as: 5,25", 160K, 48 tpi (SSDD), 8 sectors/track. This was not necessary at that time, as there was only one disk format (single sided, 160K, 8 sectors/track). The bootsector does not contain any information about the disk parameters. It is very different from the later one's (DOS 2.X. In the next figure you can see the original boot sector of PC-DOS 1.0.
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