On Tue, Mar 25, 2008 at 12:49 AM, Mike Sullivan <[EMAIL PROTECTED]> wrote: > I think this guy has a pretty good explanation of the limits of 32 bit > systems. > > http://www.dansdata.com/askdan00015.htm
He certainly covers the big issues -- hardware other than RAM using up physical address space, and Win XP SP2 not using PAE[1]. That article did lead me to MSKB 929605. As I read it, that states that Windows Vista "32-bit", which nominally supports PAE, still limits total RAM to "3.12 GB"[2]. This is done to keep various drivers from falling apart. It may be that the MS blog post I was referring to earlier was implicitly assuming "Vista" when the author stated "Windows". Or maybe I missed a qualification, or am remembering it wrong. Or maybe there's a similar limit in Win XP[3], and that's what I'm remembering. I'm not sure. Curse my feeble brain! I do find it interesting to read that even with Vista 64-bit, the license restrictions on memory can be an issue. Apparently, the 8 GiB license restriction is actually implemented in terms of physical address space, not RAM. So if you've got 8 GiB of main RAM, and dual video cards with 1 GiB video RAM each, Vista will only let you use < 6 GiB of main RAM. Microsoft may have to re-think their licensing restrictions as hardware gets bigger. [1] Technically speaking, enabling DEP (Data Execution Prevention) also enables PAE, since the NX bit (No Execute) is only present in the larger page tables that PAE gives you. But Win XP doesn't actually use PAE to support physical addresses above 4 GiB. [2] I'm not sure if this means 3.12 SI gigabytes, or 3.12 "computer" gigabytes (SI gibibytes). Microsoft usually uses the computer/binary powers. [3] Possibly inherited from the "using DEP means using PAE" issue described in [1]. -- Ben ~ Upgrade to Next Generation Antispam/Antivirus with Ninja! ~ ~ <http://www.sunbelt-software.com/SunbeltMessagingNinja.cfm> ~
