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INT 0x21 - 0x4a - DOS 2+ - Resize Memory Block

This function :

  • modifies memory block allocated by int 0x21 - 0x48.
  • can be used by program to shrink or increase the size of allocated memory


reg value descr
AH 0x4a
BX New memory size in paragraph
ES segment (block) to resize


CF is cleared if successful

CF is Set if error

reg descr
AX Error Code (0x07, 0x08, 0x09) (See Int 0x21, 0x59, Dos Error Code)
BX maximum paragraphs available for specified memory block

Notes & Comments

  • PC-DOS 2.1 and DOS 3.x will allocate the largest available block if CF is set. BX will equal the size allocated.
  • under DOS 2.1-5.0, if there is insufficient memory to expand the block as much as requested, the block will be made as large as possible
  • DOS 2.1-5.0 coalesces any free blocks immediately following the block to be resized


back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_4a.txt · Dernière modification : 2023/01/16 17:54 de