stan wrote: > Alan Cox wrote: >> On Mon, 27 Oct 2008 11:54:47 -0400 >> Matthew Flaschen <matthew.flaschen@xxxxxxxxxx> wrote: >> >>> Alan Cox wrote: >>> >>>> The moment you have more than about 900MB of RAM there are big >>>> advantages >>>> to running a 64bit kernel as it can keep all of physical and virtual >>>> space mapped at the same time, which is a big performance win. >>>> >>>> Alan > > Wouldn't you need twice as much memory to have the same memory for > applications if you are using double the word size? This is incorrect in general. GNU/Linux 32-bit uses ILP32, meaning integers, longs, and pointers all have 32 bits. GNU/Linux 64 uses LP64, which means longs and pointers have 64 bits. Integers remain 32 bits, and ASCII chars are still 8 bits (this is true of ILP64, another model, as well). Please read http://www.unix.org/whitepapers/64bit.html. > Or does the OS somehow take that into account and split the 64 bit words > into their components to get most efficient use out of them? There is no need to "split" anything. The base unit is still the byte. All 64-bit systems have 64 bit pointers, but there are no hard rules for the other types. > To clarify, I have 2 GBytes of memory in a 32 bit OS. If I use a 64 bit > OS, isn't that memory now effectively halved? No. > The same as if I use 16 bits to store a character instead of 8 bits. It is my understanding > that UTF-8 only uses the second 8 bits if it needs it. There is no "second" 8 bits. UTF-8 can use up to 4 bytes, but ASCII will use only 1 for any (sane) 64-bit implementation of UTF-8. Matt Flaschen -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
