[mythtv-users] 32 vs. 64 bit, any significant difference?

Johnny jarpublic at gmail.com
Thu Dec 17 19:05:55 UTC 2009

> People often forget that the x86-64 provides twice as many general purpose
> registers as 32-bit x86.  They have twice as many SSE registers as well.
> Depending on workload, performance can be either worse (due to larger
> pointers) or better (due primarily to the increase in registers).
> If I recall, transcoding is one of the poster children for running 64-bit.
> I don't have numbers on hand but I definitely noticed an improvement.  I
> think 15% improvement is the general rule of thumb although I've heard of
> 30% improvements when transcoding as well.  As with all such things, your
> mileage will probably vary :)

Another benefit is that the compiler can make much more efficient
optimizations because x86-64 includes all the modern changes to the
x86 ISA (SSE etc) that modern chips support. When you use 32-bit it is
compiled against the ISA that an Intel 386 used or maybe a 686 (e.g.
Pentium II, Pentium III). But I think in everyday use you aren't
likely to feel much difference from this (approximately 5%
improvement). But in processes that are very computationally intense
and benefit from newer ISA changes like SSE, then you will see larger
improvements on the order of 10%-20%. Much of the MMX and SSE
extensions added op-codes for vector operations, etc, that are
targeting at multimedia stuff like transcoding. So that is one of the
areas that sees the most benefit.

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