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File systems:

Boot sector

The Boot sector is in the beginning of each logical drive (the first sector of the track following the PT). In the start of the sector there is the Jmp command – transfer to the start of the loader code. By offset 3 there is a 8-byte length field, which contains the name and the OS version, it is not used at loading. Further, by offset 0B there is a block of 19 bytes, which describes the logical parameters of the disk – the number of bytes in a sector (for DOS-512), the number of sectors in a cluster, the number of spare sectors (i.e. the number of sectors from the start of the disk to the first FAT copy – usually one), the number of FAT copies (two), the FAT format as a text, (FAT12, FAT16 or FAT32), the root directory size (counted in entries, 32 bytes each) and the number of sectors in FAT.

All this data is written in a clear form by the Diskedit in the as Boot sector mode. At offset 2B there is the volume mark (11 bytes in length). At offset 3E is the initial loader itself. Its task is to check the first sector root directory for presence of IO.SYS and MSDOS.SYS files and, having detected them, load them to the address 0000:0700 H, after which, transfer operation to it. In the last two bytes of the sector the usual signature 55AAH is written.

Created during formatting.



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