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====== Int 31H, AH=05H, AL=04H ======

===== Version =====

1.0

===== Brief =====

Allocate Linear Memory Block

===== Input =====

  AX = 0504H
  EBX = desired page-aligned linear address of memory block, or zero if linear address unspecified
  ECX = size of block (bytes, must be nonzero)
  EDX = flags

^ Bit ^ Significance ^
| 0 | 0 = create uncommitted pages 1 = create committed pages |
| 1-31 | reserved, should be zero |
    
===== Return =====

  if function successful
  Carry flag = clear
  EBX = linear address of memory block
  ESI = handle for memory block
  
  if function unsuccessful
  Carry flag = set
  AX = error code
  8001H	unsupported function (16-bit host)
  8012H	linear memory unavailable
  8013H	physical memory unavailable
  8014H	backing store unavailable
  8016H	handle unavailable
  8021H	invalid value (ECX = 0)
  8025H	invalid linear address (EBX not page aligned)

===== Notes =====

Allocates a block of page-aligned linear address space. The base address of the block may be specified by the client, and pages within the block may be committed or uncommitted.

A DPMI 1.0 host that is 16-bit only will not support this function.

A 16-bit client of a 32-bit DPMI 1.0 host can use this function.

The allocated block is always page-aligned. If a specific linear address is not requested (EBX = 0), the DPMI host allocates the memory block at any available page-aligned linear address. If a specific linear address is requested (EBX nonzero), the host either allocates the block at the specified address or returns error code 8012H (linear memory unavailable).

Int 31H Function 0501H, which can also be used to allocate linear memory blocks, does not necessarily page-align its blocks and does not have the ability to create uncommitted pages or allocate a block at a specific linear address. 
       
===== See also =====

   

===== Note =====

Text based on [[http://www.delorie.com/djgpp/doc/dpmi/]]

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