MTRR
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On Intel P6 family processors (Pentium Pro, Pentium II and later) the Memory Type Range Registers (MTRR's) may be used to control the semantics of processor access to memory ranges. This is most useful when you have a video (VGA) card on a PCI or AGP bus. Enabling write-combining allows bus write transfers to be combined into a larger transfer before bursting over the PCI / AGP bus. This can increase performance of image write operations 2.5 times or more, at the cost of losing the simple sequential read/write semantics of normal memory.
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