[CentOS] Silly question x64 vs i386

John R Pierce pierce at hogranch.com
Wed Dec 16 21:47:19 UTC 2009


m.roth at 5-cent.us wrote:
> Longer answer: every single move, down at the machine/assembly level, can
> move twice as many bits as on a 32-bit system. That will show up as a very
> serious speed increase in your software.
>   

actually, the pentiums have had a 64bit physical memory bus since the 
first 60Mhz version, and all L1/L2 cache  <=> physical memory operations 
are 64bits.    the CPUs have all optimized things like REP MOVSB to move 
by 64bit chunks whenever possible.


The main performance advantage of x86_64 vs i686 is in the additional 
general purpose registers, this allows the compiler (or assembler 
programmer) to minimize the number of load/store instructions to 
implement a given sequence of operations.


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