David W. Hess (dwhess@banishedsouls.org) on 5/14/07 wrote:
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>This brings me back to my original question. Why did Microsoft not support the
>use of PAE and more then 32 bits of physical address space on their desktop operating systems?
>
>Was it because of marketing or technical considerations or something else?


Strictly marketing and support issues. MS does support PAE with more than 4GB of RAM on all but the smallest versions of the Server versions of Windows. Note that MS *does* use PAE on all current versions of XP if you turn the no-execute support on (the required bit is only in the PAE format page table), but without supporting more memory.

The support issues are relatively minor technically, but a real practical problem. Windows does support bounce buffering for I/O using non-LME ("Large Memory Enabled") drivers, with the attendant performance hit, and that's the first issue - *without* LME aware drivers for the critical devices (say the hard disk or the graphics device), Windows performance will be poor, and LME drivers are fairly rare for anything other than server class hardware.

Second, for some reason the number of seriously buggy LME aware drivers in the early days was just astonishing - despite these being strictly for server hardware (which you'd think would get tested fairly well), it looked like many people never bothered testing on a machine with more than 4GB of RAM.

Third, given the general quality of graphics drivers in the first place, I suspect the odds of ever getting a decently performing and stable LME version is about nil (which is not an issue for servers, of course).

Still, MS could have supported the additional memory just as a paging/caching device without any driver support.

But between the vast majority of desktop users not actually needing more memory support, and the problems, I suspect MS just never bothered for workstations, and at this point they're certainly not interested in it any more.

As others have mentioned, plenty of development happens on workstations running Windows Server, as does a fair bit of work by users who need more RAM.