Allocate Memory Block

Allocates and commits a block of linear memory.

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:

o  The allocated block is guaranteed to have at least
   paragraph  alignment.
o  This function always creates committed pages.
o  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.
o  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 Fn 0600H).
o  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 Fn 0604H.