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Posted Apr 27, 2004 21:05 UTC (Tue) by slamb (guest, #1070)
In reply to: 64-bit? by RichardRudell
Parent article: The Grumpy Editor goes 64-bit

BTW: it's not 64-bit addressing. Hypertransport has a physical limitation of 40-bits. Yeah, I couldn't believe it either until I read the specs. 1 TB is a nice improvement over 4 GB, but it's not the 2^64 talked about in an earlier post. Forget virtual address space (currently 48-bits on Opteron), I'm talking about physical address space. There is a hardwired limit which is going to hurt sooner than later.

That's not so bad. They left room in the instructions to address the full 64 bits. They'll be able to replace the hardware with something that supports the full 64 without rewriting the compilers and recompiling all the software.

IIRC, the first "32-bit" Intel machines couldn't actually address 4GB (or even 2GB) of memory, either. But it didn't really cause a problem; by the time people actually wanted to do that, they'd bought new processors. I expect this will be the same situation.

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