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more insight into BIOS MTRRs (Users)

posted by Ninho(R) E-mail, 24.03.2011, 16:56

>> That being said, if caching
>> controls are set for a given location by more than once mechanism, the
>> most restrictive (least amount of caching) policy specified wins.

Right, and quite logical too.


> Well. from what CPUID the PAT is supported and how can I check if CPU
> support pat?

I think PAT first made their appearence with Pentium 3, and AMD included them starting with K7 - Athlon XP for sure, older Athlon : don't know. My old K6-2+ certainly does not support them. But anything modern /must/.

>I guess that C2D support it. In my case MTRRLFBE sets only
> MTRRs but it works fine even with PAT not set or set by default. According
> to mentioned rule if PAT not set it shouldn't work MTRR setting but it
> worsk. But only on C2D and older. Does it mean that BIOS sets PAT but not
> set MTRR and on new core i3/5/7 it doesn't set neither MTRR nor PAT?

MTRRLBE is designed (mainly) for real mode (DOS), there paging nor the PAT mechanism can work !

--
Ninho

 

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