aragonx@xxxxxxxxxx wrote (about moving to x86_64): > I currently only have 2GB of RAM so that is not a factor. For some uses, that can be enough memory to run into 32-bit limits. > My whole reason for wanting to switch to a 64-bit kernel was performance. > I do a lot of video encoding, which is a CPU intensive application. But probably not that one. Not unless you're doing certain sorts of video editing as well. Virtual memory means that the OS kernel can pretend to programs that the computer has more memory than it really has. Each process has its own "address space", which looks to the program like its own chunk of memory to play with. In 32 bit mode, this address space is 3 GB large. This is used for everything in user-mode for this process -- program, data, memory-mapped data, scratch space, the lot. Out of that 3 GB, you'll have a "working set" for the program -- memory that is *currently* being accessed. For most programs, 3 GB is enough anyway. For most other programs, and on most computers, by the time you've used all 3 GB of address space, the working set will be large enough that you'll be swapping that to disk, and your system will be "thrashing" -- the hard disk permanently on, and everything else slowed to treacle. But for some programs, with 2 GB of real memory, if the working set size is relatively small, if the computer is running One Important Program that does make a lot of use of address space, a 3 GB limitation on address space size is the major limitation. Your working set might be 1.5 GB, the rest of the system might be swapped to disk or in the other 512 MB, but the program wants to be able to address more than 3 GB of data. In this case, you really want a 64 bit system. See, for example, http://lwn.net/Articles/75174/. I understand that even with 32 bit processes on an x64_64 kernel, the address space is 4 GB, and it's 4 TB with 64 bit processes -- and that's going to get larger with the next round of AMD processors. Hope this helps, James. -- E-mail: james@ | And the cuckoo isn't cooing, aprilcottage.co.uk | But he's cucking and he's ooing, | And a Pooh is simply pooh-ing | Like a bird. -- 'Noise', by Pooh
