Re: Athlon64 is a true 64 bits processor?
From: Anton Ertl (anton_at_mips.complang.tuwien.ac.at)
Date: 08/31/04
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Date: Tue, 31 Aug 2004 13:04:15 GMT
General Schvantzkoph <schvantzkoph@yahoo.com> writes:
>On Mon, 30 Aug 2004 23:40:20 +0100, VP wrote:
>
>> I read here
>> http://www.geek.com/news/geeknews/2002Dec/bch20021218017827.htm
>>
>> ......
>> The K8's use 48bit memory addressing (4TB or 1TB, I forget).
256TB. The K8 has 64-bit registers, 48 bits virtual address space,
and 40 bits physical address space.
>> I believe AMD
>> will add full 64bit memory
>> addressing to the K9 series, and hopefully at that point they can increase
>> the memory bitpath from 128 to
>> 256bit, as the K8 currently only deals with 128.
My K8 (Socket 754 Athlon 64) has a 64-bit memory interface, and I am
happy with that.
>> Don't think that's a big
>> factor? Look at the GFFX5900 and
>> it's predecessor.
The K8 is not a GPU, but a CPU. Caches work for CPUs (for most
applications). Compare the results for the socket 754 Newcastle with
the Socket 939 Newcastle; not a big difference.
>> This is true ? Athlon64(K8) isn't a real 64bit processor ?
It's just as real as any other 64-bit CPU (various Alpha, SPARCv9,
IA-64, MIPS-IV, HPPA-2.0 and PPC64 chips), none of which do 64-bit
virtual and 64-bit physical addressing (supposedly Power5 has 64-bit
virtual addresses, though). They all check the upper bits of the
addresses, so making the virtual addresses bigger (up to 64 bits)
won't be a problem. That's why they are called 64-bit architectures.
>Don't confuse physical addressing with virtual addressing. The AMD64 is a
>true 64 bit architecture which means that it computes 64 bit virtual
>addresses.
Sure it does. But the MMU can only translate addresses where the
upper 16 bit are all the same as bit 47 (everything else gives an
error). And Linux with its current three-level page table limit can
only deal with 41 bits or so.
- anton
-- M. Anton Ertl Some things have to be seen to be believed anton@mips.complang.tuwien.ac.at Most things have to be believed to be seen http://www.complang.tuwien.ac.at/anton/home.html
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