Datasheet

Datasheet, Volume 2 75
Processor Configuration Registers
2.5.26 TOM—Top of Memory Register
This register contains the size of physical memory. BIOS determines the memory size
reported to the OS using this register.
B/D/F/Type: 0/0/0/PCI
Address Offset: A0–A7h
Reset Value: 0000_007F_FFF0_0000h
Access: RW-KL, RW-L
Size: 64 bits
BIOS Optimal Default 000_0000_0000h
Bit Attr
Reset
Value
RST/
PWR
Description
63:39 RO 0h Reserved
38:20 RW-L 7FFFFh Uncore
Top of Memory (TOM)
This register reflects the total amount of populated physical
memory. This is NOT necessarily the highest main memory address
(holes may exist in main memory address map due to addresses
allocated for memory mapped IO). These bits correspond to
address bits 38:20 (1 MB granularity). Bits 19:0 are assumed to be
0. All the bits in this register are locked in Intel TXT mode.
19:1 RO 0h Reserved
0RW-KL 0b Uncore
Lock (LOCK)
This bit will lock all writeable settings in this register, including
itself.