Intel IA-32 - Manual (Page 482)

10-42 Vol. 3A
MEMORY CACHE CONTROL
10.12.2 IA32_CR_PAT MSR
The IA32_CR_PAT MSR is located at MSR address 277H (see to Appendix B, “Model-Specific
Registers (MSRs),” and this address will remain at the same address on future IA-32 processors
that support the PAT feature. Figure 10-7 shows the format of the 64-bit IA32_CR_PAT MSR.
The IA32_CR_PAT MSR contains eight page attribute fields: PA0 through PA7. The three low-
order bits of each field are used to specify a memory type. The five high-order bits of each field
are reserved, and must be set to all 0s. Each of the eight page attribute fields can contain any of
the memory type encodings specified in Table 10-10.
Figure 10-7. IA32_CR_PAT MSR
Note that for the P6 family processors, the IA32_CR_PAT MSR is named the PAT MSR.
31 27 26 24 23 19 18 16 15 11 10 8 7 3 2 0
Reserved PA3 Reserved PA2 Reserved PA1 Reserved PA0
63 59 58 56 55 51 50 48 47 43 42 40 39 35 34 32
Reserved PA7 Reserved PA6 Reserved PA5 Reserved PA4
Table 10-10. Memory Types That Can Be Encoded With PAT
Encoding Mnemonic
00H Uncacheable (UC)
01H Write Combining (WC)
02H Reserved*
03H Reserved*
04H Write Through (WT)
05H Write Protected (WP)
06H Write Back (WB)
07H Uncached (UC-)
08H - FFH Reserved*
NOTE:
* Using these encodings will result in a general-protection exception (#GP).