8/25/2023 0 Comments Floppy disk format commands![]() The normal setting is code 2 (512 bytes). The size code (N) can take on any one of the four standard values shown below: N | Sector Size (bytes) | Sector Size (KB) The cylinder and head parameters are not actually needed in this address mark because the read/write head is positioned mechanically at the proper track and the side is selected electronically, but they are recorded and tested as a safety check. When a sector is being read or written, the diskette controller searches the diskette track for the sector's ID, the essential part of which is R, the record or sector number. The 4 bytes are referred to as C for cylinder, H for head, R for record (or sector number), and N for number of bytes per sector (also called the size code). The 4 bytes of data associated with a sector on the disk are known as address marks and are used by the disk controller to identify individual sectors during the read, write, and verify operations. When you format a disk track, the 4-byte groups are written to the diskette immediately in front of the individual sectors in the track. ![]() You specify these 4 bytes for each sector to be formatted by creating a table of 4-byte groups and passing the table's address in the register pair ES:BX. In the words of Peter Norton, from The New Programmer's Guide to the IBM PC and PS/2:Įvery sector on a diskette track has 4 descriptive bytes associated with it. If CF is set, then an error occurred and the AH register contains the error code. If the interrupt returns with the carry flag ( CF) clear, then no error occurred and the AH register will contain 0.
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