4. Flat Model

• The flat memory model is a non-segmented configuration available in 32-bit operating systems.

• Flat model is similar to tiny model in that all code and data go in a single 32-bit -addressable block of memory.

• To write a flat model program, specify the .386 or .486 directive before .MODEL FLAT:

      .386
      .MODEL FLAT
      ; All data and code, including system resources, are in a single 32-bit segment.
  

• The operating system automatically initializes segment registers at load time.

• A program may need to modify segment registers only when mixing 16-bit and 32-bit segments in a single application.

• CS, DS, ES, and SS all occupy the supergroup named FLAT.

• Addresses and pointers passed to system services are always 32-bit near32 addresses and pointers.

• Flat model does not require far addresses. By default, all addressing is relative to the initial values of the segment registers.

• Therefore, far addressing does not apply to flat model programs.