MEM F000h:FFE0h - COMPAQ 386 MACHINES Size: 16 BYTEs SeeAlso: MEM 80C00000h Format of Compaq 386 Memory Configuration Data: Offset Size Description (Table M0134) 00h WORD Compaq 32-bit extra built-in memory available (FFFFh if not) 02h WORD Total size of Compaq extra memory 04h WORD Count of available paragraphs of Compaq extra memory 06h WORD ParagraphA 16-byte unit of memory. This size is the result of the 8086's segmentation model, where incrementing the segment by one advances the absolute location by 16 bytes. address of last paragraph in use as Compaq extra memory 08h 2 BYTEs product class signature "03" 0Ah 6 BYTEs signature "03COMPAQ" Notes: The full "03COMPAQ" signature can be found in (at least) Compaq 386 machines which have dual harddisk controller. (see also CMOS(Complementary Metal-Oxide-Semiconductor) A type of integrated circuit design known for its low power consumption. 70h) However, the 6-byte "COMPAQ" signature also seems to be available in other Compaq machines with dual hard disk controllers, at least the MS-DOS/PCIBM PC DOS IO.SYS/IBMBIO.COM checks for if before it calls INT 15/AX=E400h and INT 15/AX=E480h. Compaq's extra memory is mappable memory starting at FE00h:0000h growing downwards. It can be made available for example with Novell DOS 7+ EMM386.EXE /COMPAQ=ON. Although this structure resides at a ROM-address it is actually write- protected RAM(Random Access Memory) See also DRAM, SRAM.. To write to the structure to map in Compaq extra memory the write-protection must be temporarily disabled by setting bit 1 at WORD 80C00000h.