Allocate Memory Block

Call With

AX = 0501H
BX:CX = size of block (bytes, must be nonzero)

Returns

if function successful
Carry flag = clear
BX:CX = linear address of allocated memory block
SI:DI = memory block handle (used to resize and free block)

if function unsuccessful
Carry flag = set
AX = error code

8012H	linear memory unavailable
8013H	physical memory unavailable
8014H	backing store unavailable
8016H	handle unavailable
8021H	invalid value (BX:CX = 0)

Notes

• The allocated block is guaranteed to have at least paragraph alignment.

• This function always creates committed pages.

• This function does not allocate any descriptors for the memory block. It is the responsibility of the client to allocate and initialize any descriptors needed to access the memory with additional DPMI function calls.

• Under DPMI hosts that support virtual memory, the memory block will be allocated unlocked. The client can lock some or all of the memory after it is allocated with the Lock Linear Region function (Int 31H Function 0600H).

• Under many DPMI hosts, allocations by this function are page granular. This means, for example, that if the DPMI host uses a page size of 4 KB (1000H), an allocation of 1001H bytes will actually result in an allocation of 2000H bytes. Therefore, it is best to always allocate memory in multiples of the unit of granularity (under DPMI 0.9, use 4K bytes), which can be obtained with Int 31H Function 0604H.