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

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MTRRs Added

Know the Characteristics of Your Target

Introduction

When the processor must perform a memory access, it is important that it have an understanding of the characteristics of the type of device that occupies the memory address to be accessed. If it does not, the manner in which the memory access is performed may result in improper operation of the device or of the program.

Why the Processor Must Know the Memory Type

As an example, assume that an area of memory is populated with a series of memory-mapped IO registers associated with one or more IO devices. Now assume that the program performs a 4-byte memory read to obtain the status of a device from a 32-bit, device-specific status register. If the processor were to assume that the ...

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