Author: Robert Hyatt
Date: 15:08:07 10/25/01
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On October 25, 2001 at 13:45:05, Tom Kerrigan wrote: >On October 25, 2001 at 11:53:09, Robert Hyatt wrote: > >>For 64 bit development since mid-60's, the driving force has been a push for >>more precision in FP (64 bits) and _faster_ execution (because all 32 bit >>computers from the 60's had double-precision (64 bit FP) but it was too slow.) > >As I said in another post, FP has very little to do with the bitiness of a chip. >Everybody agrees that x86s are 32-bit, but the P4 has 128-bit wide SIMD >registers and double precision FP ALUs. That doesn't matter. _how_ do you gate the FP values around _inside_ the cpu? On 64 bit datapaths or multiplexed on 32 bit datapaths? That is the performance issue. 32 bit machines multiplex the data and it hurts performance. The 64 bit boxes (alpha, mips, cray, etc) don't require two datapath transfers per single operand... > >-Tom
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