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Basic Disk Operating System (BDOS) Functions
The region beginning at paragraph address 700H is now available for allocation in
the next request. Note that a memory request will fail if eight memory regions have
already been allocated. Normally, if all program units can reside in a contiguous
region, the system allocates only one region.
MEMORY CONTROL BLOCKS (MCB)
Memory management functions (functions 53-57) reference a Memory Control
Block (MCB), defined in the calling programs, which takes the form:
16-bit
16-bit
8-bit
MCB:
M-Base
M-Length
M-Ext
where M-Base and M-Length are either input or output values expressed in 16-byte
paragraph units, and M-Ext is a returned byte value, as defined specifically with
each function code. An error condition is normally flagged with a OFFH returned
value in order to match the file error conventions of CP/M-80.
GET MAXIMUM MEMORY
ENTRY
CL:
35H
DX: Offset
ofMCB
FUNCTION 53
GET MAX MEM
RETURN
AL: Return Code
The Get Maximum Memory function finds the largest available memory region
which is less than or equal to M-Length paragraphs.
If
successful, M-Base is set to
the base paragraph address of the available area and M-Length to the paragraph
length. Register AL returns the value OFFH if no memory is available, and OOH if
the request was successful. M-Ext is set to 1 if there is additional memory for
allocation, and 0 if no additional memory is available.
4-35
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