"While 64-bit support is now considered common for both Intel and AMD processors, many Linux (as well as Windows) users are uncertain whether to use a 32-bit or 64-bit operating system with there being advantages for both paths. With this being the last Phoronix article for 2006, we decided to take this opportunity to look at the common question of whether to use 32-bit or 64-bit software. In this article, we will be comparing the i386 and x86_64 performance with Ubuntu 6.10 Edgy Eft and Ubuntu 7.04 Feisty Fawn Herd 1 to see how the numbers truly stack up."
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Member since:2006-11-05
Well, it does if you have to save them to main memory (context switches, for instance). Inside the CPU, as you say, it makes no difference.
I should also have noted in my original post that 64 bit architectures vastly speed up computational work involving 64-bit integerss or very precise floating point values. This is really noticeable in scientific applications (physics simulations for instance).
Member since:2005-07-07
There should be no impact on floating point operations, since the x86 FPU registers are 80 bits wide and is capable of handling the common 64 bit double precision floating point with ease (with the additional 16 bits for overflow). This is why you rarely see any improvement in FP heavy code when moving from x86 - x86-64.
The move from 32 bit to 64 bit doesn't affect floating point.
Member since:2005-07-06
Net result is no difference.
Not quite true. 64-bit programs use more memory than 32-bit ones. As such, less memory is available for the system to use, more bandwidth is used shuttling the program around in memory, and since less memory is available, less things can be cached, etc.
Member since:2005-07-07
Actually x86 chips have used larger datapaths under the hood for years. They will write/read combine multiple 32bit accesses together into larger chunks (e.g. 64bit) - so it's moot. The first post is right - on one hand you get more registers, on the other you need to throw more memory around if it contains pointers of any sort.
Member since:
2006-03-23
"1. Words become twice as large. When you have to swap registers around, you have to move twice as much data. This makes the system slow down."
The words are twice as wide but so are the data paths.
Net result is no difference.