On Mon, Mar 24, 2008 at 8:29 PM, Mike Gill <[EMAIL PROTECTED]> wrote: >> This isn't just about PAE. In some cases, XP apparently refuses to >> recognize RAM located below the 4 GiB mark on the physical address >> bus, but which is not used by other hardware. Exact circumstances and >> explanations are unclear and/or poorly documented. > > Well, what I'm talking about is about PAE.
Well... good for you. :) The thread, and my first message in it (the one you replied to), was about how and why Windows XP utilities RAM -- or not. That's apparently not just about PAE. > That is if we're talking about 4GB of memory, 4GB of physical address space, > and Windows XP/2K3. I don't think it's poorly documented or worded > necessarily. XP > is built with the restriction by design as plainly mentioned on Microsoft's > PAE webpage: Yes. I know. I've said so. Several times now. :) On i386, without PAE, you have a 4 GiB physical address space. Hardware other than RAM will always eat into that. Thus, you can never address a full 4 GiB of RAM. However, Windows XP apparently has some additional limitations beyond that, which are not clear or well documented. The poorly documented/unclear part is that XP apparently sometimes recognizes much less than 4 GiB of RAM -- far more so than that which can be explained solely by other hardware using up physical address space. That isn't about PAE. I never meant to suggest that Windows XP supports PAE. One point I was making, originally, was that with PAE, a "32-bit" OS can utilize more than 4 GiB of RAM, and that some versions of "32-bit Windows" can do so, and thus it isn't a processor limitation that keeps Win XP from using 4 GiB of RAM. But *that* is unrelated to the other apparent limits mentioned above. >> Hardware which properly supports the full PCI spec, and with >> software which properly handles physical addresses above 4 GiB, can >> support physical addresses above the 4 GiB mark. Those physical >> addresses will be mapped into the 4 GiB virtual address space. > > What's the point? If XP (and some 2K3/8's) can't address above that barrier > then what good would it do to run them in a system that only supports up to > 4GB in the first place? The point of my explaination above was to try to increase mutual understanding. It seemed like there was some confusion over what I was trying to communicate. I was not trying to suggest that putting hardware above the 4 GiB physical address mark would be useful to Windows XP. -- Ben ~ Upgrade to Next Generation Antispam/Antivirus with Ninja! ~ ~ <http://www.sunbelt-software.com/SunbeltMessagingNinja.cfm> ~
