Reply to post: Re: AMD Dreams

Linus Torvalds drops Intel and adopts 32-core AMD Ryzen Threadripper on personal PC

John PM Chappell

Re: AMD Dreams

"The big gain in the move to x86_64 was the ability to directly address more than 4G of RAM. At the time ('05?) that was becoming important."

No. It was already and had been for a long time, possible to do that. Address lines rarely map directly to the the instruction size (they don't for the AMD64 current architecture, either) and physical memory addressing is orthogonal to instruction size. There is no "4G (sic)" limit. It's true that you need more than 32 bits for a memory address higher than 4 GiB but that's actually nothing to do with the processor's instruction size - 32 bit processors were addressing more than that long before people were worrying about it being a problem. PAE was the standard that addressed it, and it dates to 1995 (Pentium Pro), it also was directly extended to form the standard for memory addressing used in the AMD64 architecture.

You may be confusing the issue with a Microsoft *licensing* decision to begin restricting 32 bit MS desktop OSes from addressing memory at addresses higher than 4 GiB. A detailed analysis of that can be found here https://www.geoffchappell.com/notes/windows/license/memory.htm (no relation, as far as I know).

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