On Tue, 11 May 2010 09:17:38 -0500 Aaron Konstam <akonstam@xxxxxxxxxxxxx> wrote: > On Tue, 2010-05-11 at 06:33 -0400, John Aldrich wrote: > > Just a question here... are you running a 32-bit version of Fedora or a 64- > > bit version? 32-bit versions will only show about 3 gigs of memory, no > > matter how much if you have 20 Gigs, you'll only see 3. > > I would expect 32 bit machinews to be able to handle 4G of memory. > 2^32=4G It isn't quite that simple in either direction. Most x86 processors have a 32bit virtual but a 36 or even 40bit physical address space. So you can "handle" very large amounts of memory. In fact if you have 4GB of RAM the kernel is probably seeing 4.25GB or so - because of the graphics card memory, PCI devices etc. > And the putput of free tells me he has roughly 4G of memmory reported. The x86 has a 4GB virtual address space and in some cases a 36bit physical one. So you can have up to above 64GB of memory in theory but only 4GB of anything can be mapped at a time. To get performance you need the user address space (3GB), the kernel, some virtual mappings and some of memory mapped so we have to do a lot more work when there is over about 1GB of physical RAM. The practical impact tends to be that above 1GB of memory (actually about 900Mb due to kernel mappings) the 64bit kernel performs better, and as you head above 4GB it rapidly increases its advantage as the 32bit kernel has to spend all its time changing what it has mapped (think of it like reading a book versus seeing the entire thing as a poster, the 32bit kernel spends all of its time adjusting the pages it can see) -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
