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>Microsoft refused to support physical address extensions in XP Completely wrong "The original releases of Windows XP and Windows XP SP1 used PAE mode to allo

>Microsoft refused to support physical address extensions in XP Completely wrong "The original releases of Windows XP and Windows XP SP1 used PAE mode to allow RAM to extend beyond the 4 GB address limit. However, it led to compatibility problems with 3rd party drivers which led Microsoft to remove this capability in Windows XP Service Pack 2. Windows XP SP2 and later, by default, on processors with the no-execute (NX) or execute-disable (XD) feature, runs in PAE mode in order to allow NX.[14] The no execute (NX, or XD for execution disable) bit resides in bit 63 of the page table entry and, without PAE, page table entries on 32-bit systems have only 32 bits; therefore PAE mode is required in order to exploit the NX feature. However, "client" versions of 32-bit Windows (Windows XP SP2 and later, Windows Vista, Windows 7) limit physical address space to the first 4 GB for driver compatibility via the licensing limitation mechanism, even though these versions do run in PAE mode if NX support is enabled. Windows 8 will only run on processors which support PAE, in addition to NX and SSE2." - http://en.wikipedia.org/wiki/Physical_Address_Extension#Microsoft_Windows http://en.wikipedia.org/wiki/Physical_Address_Extension#Micr...

zanny 12y ago
The driver instability was only their fault. The fact is the reason AMD64 "won" was because in the late 2004 era, with SP2, Microsoft killed PAE (the concept, not the implementation, by artificially limiting addressable memory), and the artificial memory limit on 32 bit systems doomed the architecture. I speak only of the time period from 2004 - 2008 where we went from Pentium 4 to Core 2 (and Athlon64 to Phenom), where 64 bit became ubiquitous because Microsoft failed to provide its consumer grade OSes the ability to access the amounts of memory the hardware supported.
- joenathan 12y ago
  Everyone crapped on Microsoft because there were no x64 drivers for Vista, and the 3rd party manufacturers didn't want to create new drivers for their old hardware. It's Microsoft's fault that 3rd party driver support sucks? So they get blamed with they keep compatibility as in the case of PAE on x86 and blamed when they break it.
- yuhong 12y ago
  To be more precise, they changed the 4GB physical memory limit to a physical address space limit. MS never intended even XP SP1 to officially support PAE, but the code happened to treat the 4GB limit as a physical memory limit. When XP SP2 added NX support which required PAE, driver compatibility forced MS to add the physical address space limit.

zanny 12y ago

The driver instability was only their fault. The fact is the reason AMD64 "won" was because in the late 2004 era, with SP2, Microsoft killed PAE (the concept, not the implementation, by artificially limiting addressable memory), and the artificial memory limit on 32 bit systems doomed the architecture. I speak only of the time period from 2004 - 2008 where we went from Pentium 4 to Core 2 (and Athlon64 to Phenom), where 64 bit became ubiquitous because Microsoft failed to provide its consumer grade OSes the ability to access the amounts of memory the hardware supported.

joenathan 12y ago
Everyone crapped on Microsoft because there were no x64 drivers for Vista, and the 3rd party manufacturers didn't want to create new drivers for their old hardware. It's Microsoft's fault that 3rd party driver support sucks? So they get blamed with they keep compatibility as in the case of PAE on x86 and blamed when they break it.
yuhong 12y ago
To be more precise, they changed the 4GB physical memory limit to a physical address space limit. MS never intended even XP SP1 to officially support PAE, but the code happened to treat the 4GB limit as a physical memory limit. When XP SP2 added NX support which required PAE, driver compatibility forced MS to add the physical address space limit.