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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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MSRs Added

General

The Pentium® processor was the first IA32 processor to implement Model Specific Registers (MSRs) and the two instructions that are used to access them:

  • RDMSR instruction. The numeric ID of the MSR to be read is placed in ECX and the RDMSR instruction is then executed. The 64-bit content of the MSR is placed in the EDX:EAX register pair, with the 32 msbs in EDX and the 32 lsbs in EAX.

  • WRMSR instruction. The numeric ID of the MSR to be written to is placed in ECX, the data to be written is placed in the EDX:EAX register pair and the WRMSR instruction is then executed.

The RDMSR and WRMSR instructions can only be executed by programs running at privilege level 0.

The Pentium® implemented the MSRs described in Table 21-1 on page ...

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