Re: Athlon64 is a true 64 bits processor?

From: General Schvantzkoph (schvantzkoph_at_yahoo.com)
Date: 08/31/04 

Date: Mon, 30 Aug 2004 20:08:40 -0400

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). 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. Don't think that's a big
> factor? Look at the GFFX5900 and
> it's predecessor. Imagine a 2 lane
> ....
> This is true ? Athlon64(K8) isn't a real 64bit processor ?
>
> VP

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. Virtual addresses are translated into physical addresses which
is whats used to access actual DRAM. A big DIMM in today's technology is
1G which means that to fill a 48 bit physical address space you would need
2^18 DIMMs, i.e. 256K DIMMs. Most motherboards have 4 DIMMs which is a
long way from 256K. If Moore's law could go on forever, and it can't, then
at 1 bit every 18 months (the traditional Moore's law rate) it will take
another 24 years before you could buy four DIMMs that would require all 48
bits to address them.

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