Daniel Eran Dilger
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Road to Mac OS X Snow Leopard: the future of 64-bit apps

Prince McLean, Apple Insider
Snow Leopard’s across-the-board leap to 64-bits, from the kernel to all of its bundled apps, will make more memory available and boost performance. However, Apple will also need to manage its 64-bit lead and organize its developers. Here’s why.
Following the initial introduction to 64-bit computing leading up to Snow Leopard, a second segment outlining issues related to the amount of RAM that can be installed and actually used by the system, and a third segment examining how much memory a specific app can use and how performance will improve with 64-bit addressing, this fourth segment will look at how the market for 64-bit apps is unfolding and how Apple has pioneered 64-bits on the desktop.

Road to Mac OS X Snow Leopard 1: 64-bits
2: 64-bits, Santa Rosa and the great PC swindle
3: Twice the RAM, half the price, 64-bits
4: the future of 64-bit apps


1 rjackb { 09.06.08 at 1:34 am }

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.

2 chelgrian { 09.06.08 at 10:36 am }

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.

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