On Sun, 2012-05-06 at 10:02 -0400, jordan wrote: > And you would be correct to do so ;) Martin seems to be ignoring all > of the benefits of 64bit CPUs, and only considering the RAM side of > things; > A lot of people seem to think that you can't address 4GB of RAM with a 32 bit OS, which isn't true of course. However there is an effect, particularly under Windows, on the size of an individual process: IIRC Windows grabs half the process space for itself while Linux only grabs the top 25%. I don't have a reference for that or I'd include it. However, this is probably neither here nor there for most people: not many of us do the sort of heavy duty rendering or video editing that needs several GB per process and they will all have considerably more RAM installed, so a 64 bit OS will be mandatory. > > In view of this its worth pointing out that, unless you have more than > > 4GB of RAM installed, there should be no need to run a 64 bit OS. > > As a matter of FACT - Your above statement is incorrect. Using 64bit > has more implications than just being able to use 4+gig of ram. Sure, > 64bit tends to use more memory, but using 64bit offers (significantly) > better performance being as you can directly use 64bit data structures > / 64bit registers / address spaces. > That's not true. A more correct statement is that a 64 bit version of the same program MAY run faster than a 32 bit version on a CPU with the same speed and core count. Simply using longer registers has almost no effect because only a small proportion of instructions in any program will involve 64 bit operands apart from address referencing in the 64 bit version (of course) and so any speed increase will be entirely due to whether the compiler optimiser takes advantage of the extra registers in the 64 bit CPU. Some compilers may do this. Others won't. Any speed gains here must be offset against the cost of reading the bigger 64 bit binary into memory and the impact of the extra code size on L1 and L2 caching. Its also possible that JIT systems like the Java JVM will look at the number of available registers at runtime and optimise accordingly, in which case a 32 bit JVM would run at the same speed as a 64 bit one. > I'd also like to point out that telling someone with some /lib32 > issues, to install a 32bit OS is not a solution. > Only true if the problem is bugs in the library. Most of the 64 bit problems appearing on this list are due to the absence of said 32 bit libraries, typically those required by video drivers, not to the bugs in them. Martin
