Why the 64 bit ISA is better

[Stan Hoeppner <stan@hardwarefreak.com>]

Given the recent threads regarding 32 vs 64 bit I thought I'd take a
moment to present information often omitted in responses to these posts.

First, the i386 kernel/user space have access to only the original 8
general purpose registers of the 80386 ISA that are 32 bits wide, and
cannot generally access the more recent multimedia/floating point
registers used for things like SSE3/4 and AVX.

The AMD64 ISA has twice as many GPRs and twice as wide, 16 general
purpose registers each 64 bits wide, and also can access the 128 bit and
256 bit wide multimedia/FP registers of the newest CPUs, allowing for
SSE3/4, AVX, etc.  These give greatly enhanced performance for some
kernel operations (md RAID5/6 for example) and many applicaitons.

So beyond the advantage of linear memory addressing far beyond the 4GB
limit of the i386 kernel/apps, the AMD64 kernel/apps have some serious
performance advantages.

-- 
Stan