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Basic I/O System (BIOS) Functions
SET TRACK NUMBER
ENTRY
cx:
Track Number
FUNCTION 10
SETTRK
RETURN
This function sets a track number. Register CX contains the track number for
subsequent disk accesses on the currently selected drive. Programs can seek the
selected track at this time, or delay the seek until the next read or write actually
occurs. Register CX can take values in the range 0-76 (for floppy diskettes) and
0-720 (for hard disk) corresponding to valid track numbers. A call to this function
with the value 00 in CX is equivalent to a call to function 8.
SET SECTOR NUMBER
ENTRY
CX: Sector Number
FUNCTION 11
SETSEC
RETURN
This function sets a sector number. Register CX contains the translated sector
number (see function 16) for subsequent disk accesses on the currently selected
drive. Programs can send this information to the controller at this point, or delay
sector selection until a read or write operation occurs. The BIOS uses a combination
of track number and sector number to determine the physical location of data on a
diskette.
• For single-sided, single-density diskettes (lD), there are 26 sectors (num-
bered 1-26) per track, and one track per cylinder.
• For double-sided, double-density diskettes (2D), there are 26 sectors
(numbered 1-26) per track, and two tracks (numbered 0 and 1) per cylinder.
Track 1, sector 1 refers to cylinder 0, sector 52.
• For hard disks, there are 64 logical sectors (numbered 1-64) per track, and 8
tracks per cylinder.
See Chapter 7 for more complete addressing information.
5-13
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