Comments on: Road to Mac OS X Snow Leopard: the future of 64-bit apps http://www.roughlydrafted.com/2008/09/05/road-to-mac-os-x-snow-leopard-the-future-of-64-bit-apps/ Daniel Eran Dilger in San Francisco Sun, 05 Feb 2012 17:03:33 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: chelgrian http://www.roughlydrafted.com/2008/09/05/road-to-mac-os-x-snow-leopard-the-future-of-64-bit-apps/comment-page-1/#comment-12070 chelgrian Sat, 06 Sep 2008 14:36:54 +0000 http://www.roughlydrafted.com/?p=2361#comment-12070 All other things being equal, and the additional virtual address space not being needed, 64 bit only slows things down due to increasing cache requirements and memory bandwidth requirements. Going from 32 to 64 bit has no influence on ALU operations , like adds, as the hardware is designed in the first place to do 64 bit operations and the extra silicon this takes is dwarfed by the number of transistors needed to implement ever larger caches. However in the case of x86_64 all other things are not equal. The x86 instruction set has always been register starved it only has 8 general purpose registers (and a some of these aren't really general purpose and have limitations on their use). The AMD64/x86_64 extension extends this to 16 GP registers, if you have enough memory band width and cache to offset the increased requirements then the move from 8 to 16 GP registers can give you a performance increase of the order of 30%. If you look at other OSes/architectures which have been 64 bit for a long time such as Solaris/SPARC or AIX/POWER the vast majority of the binaries run on them are 32 bit as there is no penalty in registers for doing so and the binary will be faster than a 64 bit binary unless the extra address space is needed. All other things being equal, and the additional virtual address space not being needed, 64 bit only slows things down due to increasing cache requirements and memory bandwidth requirements. Going from 32 to 64 bit has no influence on ALU operations , like adds, as the hardware is designed in the first place to do 64 bit operations and the extra silicon this takes is dwarfed by the number of transistors needed to implement ever larger caches.

However in the case of x86_64 all other things are not equal. The x86 instruction set has always been register starved it only has 8 general purpose registers (and a some of these aren’t really general purpose and have limitations on their use). The AMD64/x86_64 extension extends this to 16 GP registers, if you have enough memory band width and cache to offset the increased requirements then the move from 8 to 16 GP registers can give you a performance increase of the order of 30%.

If you look at other OSes/architectures which have been 64 bit for a long time such as Solaris/SPARC or AIX/POWER the vast majority of the binaries run on them are 32 bit as there is no penalty in registers for doing so and the binary will be faster than a 64 bit binary unless the extra address space is needed.

]]> By: rjackb http://www.roughlydrafted.com/2008/09/05/road-to-mac-os-x-snow-leopard-the-future-of-64-bit-apps/comment-page-1/#comment-12060 rjackb Sat, 06 Sep 2008 05:34:35 +0000 http://www.roughlydrafted.com/?p=2361#comment-12060 So why, specifically, do you think that 64-bit computing will boost performance? Sure, you have a larger address space but how many people really need that? It's great for databases and the like but how many ordinary people using ordinary applications will benefit from a larger address space? If you are performing ordinary operations, such as adding 2 + 2, then using 32-bit operations will almost certainly be faster than 64-bit ones. So why, specifically, do you think that 64-bit computing will boost performance? Sure, you have a larger address space but how many people really need that? It’s great for databases and the like but how many ordinary people using ordinary applications will benefit from a larger address space? If you are performing ordinary operations, such as adding 2 + 2, then using 32-bit operations will almost certainly be faster than 64-bit ones.

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