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  Function 48H (decimal 72) dynamically allocates memory. You request the
  number of paragraphs (16-byte units) you want allocated in BX. On return,
  AX contains the segment of the allocated memory block.

  If an error occurs, the carry flag is set and AX contains an error code:
  07H (memory control blocks destroyed) or 08H (insufficient memory). If
  there is insufficient memory to satisfy your request, BX contains the
  size, in paragraphs, of the largest available block of memory.

  Memory blocks allocated to a program using function 48H are freed by DOS
  when the program terminates with function 00H or 4CH, but they remain
  allocated to a memory-resident program that terminates with the
  Terminate-and-Stay-Resident function, 31H.