Posted Apr 27, 2004 21:05 UTC (Tue) by slamb
In reply to: 64-bit?
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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