1-6 Technical Information
Non-cacheable portions of memory are defined by software (see the following subsection
for a system memory map). The system does not cache the following regions:
n
video text memory block from A0000 to BFFFF
n
PCI memory space on top of main memory to 4 GB
n
any access to the PCI or AT bus
The cache can be cleared by software instructions.
System and Video BIOS
The system and video BIOS are stored in a 1 MB (128 KB by 8) flash memory device
(Flash ROM). The system BIOS uses 64 KB, the video BIOS uses 32 KB, and 32 KB is
reserved. The system BIOS is capable of being shadowed and cached through the system's
Setup utility (see Section 2 for Setup information). System BIOS is write protected and
automatically enabled.
The BIOS programs execute the Power-On Self-Test, initialize processor controllers, and
interact with the display, diskette drives, hard disks, communication devices, and
peripherals. The system BIOS also contains the Setup utility. The hardware setup default
copies the ROM BIOS into RAM (shadowing) for maximum performance.
The Flash ROM allows the system and video BIOS to be upgraded with the BIOS Update
utility, without removing the ROM (see Section 2 for further information on the BIOS
Update utility). The Flash ROM supports the reprogramming of the system BIOS and the
video BIOS.
The system memory map in shown in Table 1-2.
Table 1-2 System Memory Map
Memory Space
Size
To
Function
FFF80000-FFFFFFFF
512 KB
4 GB
BIOS ROM
04000000-07FFFFFF
64 KB
128 MB
Second level cache (non-cacheable)
First level cache (cacheable)
01000000-03FFFFFF
48 KB
64 MB
Always cacheable
00F00000-00FFFFFF
1 MB
16 MB
Optional memory space gap
00100000-00EFFFFF
14 MB
15 MB
Cacheable
000F0000-000FFFFF
64 MB
1KB
System BIOS (shadowed in DRAM)
000C8000-000EFFFF
160 KB
960 KB
Expansion region (shadowed in DRAM)
000C0000-000C7FFF
32 KB
800 KB
Video BIOS (shadowed in DRAM
000A0000-000BFFFF
128 KB
768 KB
Video buffer (SMM space non-cacheable)
