DOS Fn 4aH: Shrink or Expand a Memory Block

                                                         Compatibility: 2.0+ 
 Expects: AH    4aH
          ES    segment of an allocated memory block
          BX    desired size for the block, in paragraphs (16-byte chunks)
 Returns: AX    error code if CF is set to CY
          BX    largest block available (if a "grow" request fails)
    Info: Changes the size of an existing memory block.

          When a program receives control, the 4bH EXEC function has
          allocated a memory block starting at the PSP that contains all of
          available memory.  To make memory available to EXEC a child
          process, shrink the block starting at your PSP paragraph.

   Notes: ■ DOS Fn 31H and INT 27H shrink the block at the PSP.

          ■ .COM programs: Move your stack down BEFORE shrinking your

See Also: Memory Control Functions
          Memory Control Block
          DOS Functions