User`s guide

BDOS FUNCTION 27: GET ADDR(ALLOC)

Entry Parameters:

Returned Value:

CP/M 3 maintains an allocation vector in main memory for each active disk drive.

Some programs use the information provided by the allocation vector to determine

the amount of free data space on a drive. Note, however, that the allocation infor-

mation might be inaccurate if the drive has been marked Read-Only.

Function 27 returns in register pair HL, the base address of the allocation vector

for the currently selected drive. If a physical error is encountered when the BDOS

error mode is one of the return modes (see Function 4S), Function 27 returns the

value OFFFFH in the register pair HL.

In banked CP/M 3 systems, the allocation vector can be placed in bank zero. In

this case, a transient program cannot access the allocation vector. However, the

BDOS function, Get Disk Free Space (Function 46), can be used to directly return

the number of free 128-byte records on a drive. The CP/M 3 utilities that display a

drive's free space, DIR and SHOW, use Function 46 for that purpose.

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BDOS Function Calls CP/M 3 Programmers Guide