mtrr

MTRR是Memory Type Range Register的縮寫，可翻譯為存儲區域類型暫存器，它規定了讀寫某段範圍物理記憶體的策略，用於最佳化CPU數據傳送性能。例如可將MTTR設為在顯存的地址範圍上使用“write-combining”策略，CPU能夠在PCI/AGP匯流排上，將許多次少量的數據寫入集合成一次大的數據寫入，這樣能獲得 2.5倍以上圖像傳送速度的提升。
Memory Type Range Registers (MTRRs) are control registers that are used as a control mechanism which provides system software with control of how accesses to memory ranges by the CPU are cached. It uses a set of programmable model-specific registers (MSRs) which are special registers provided by most modern CPUs.
Possible access modes to memory ranges can be:
* uncached
* write-through
* write-combining
* write-protect
* write-back
Additional bits which are provided on some computer architectures such as AMD64 allow the shadowing of ROM contents in system memory (Shadow ROM) and the configuration of memory-mapped I/O.
In write-back mode, writes are written to the CPU's cache and the cache is marked dirty, so that its contents are written to memory later)
Write-combining allows bus write transfers to be combined into a larger transfer before bursting them over the bus to allow more efficient writes to system resources like graphics card memory. This often increases the speed of image write operations by 2.5 times, at the cost of losing the simple sequential read/write semantics of normal memory.