User`s guide

BDOS FUNCTION 46: GET DISK FREE SPACE
Entry Parameters:
Registers C: 2EH
E: Drive
Returned Value: First 3 bytes
of current DMA
buffer
Registers A: Error Flag
H: Physical Error
The Get Disk Free Space function determines the number of free sectors, 128 byte
records, on the specified drive. The calling program passes the drive number in
register E, with 0 for drive A, 1 for B, and so on, through 15 for drive P in a full 16-
drive system. Function 46 returns a binary number in the first 3 bytes of the current
DMA buffer. This number is returned in the following format:
fso fsl fs2
Disk Free Space Field Format
fso = low byte
fsl = middle byte
fs2 = high byte
Note that the returned free space value might be inaccurate if the drive has been
marked Read-Only.
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BDOS Function Calls CP/M 3 Programmers Guide