Specification Sheet

Datasheet, Volume 2 of 2 33
Processor Configuration Register Definitions and Address Ranges
2.4 Legacy Address Range
The memory address range from 0 to 1 MB is known as Legacy Address. This area is
divided into the following address regions:
• 0 – 640 KB - DOS Area
• 640 – 768 KB - Legacy Video Buffer Area
• 768 – 896 KB in 16 KB sections (total of 8 sections) – Expansion Area
• 896 – 960 KB in 16 KB sections (total of 4 sections) – Extended System BIOS Area
• 960 KB – 1 MB Memory, System BIOS Area
The area between 768 KB – 1 MB is also collectively referred to as PAM (Programmable
Address Memory). All accesses to the DOS and PAM ranges from any device are sent to
DRAM. However, access to the legacy video buffer area is treated differently.
Assumption: GT never sends requests in the Legacy Address Range. Thus, there is no
blocking of GT requests to this range in the System Agent.
Figure 2-3. DOS Legacy Address Range