[Off-topic] Re: Build an erlang computer (was:Computers are fast)

David Hopwood <>
Wed Jan 25 21:54:41 CET 2006


Joe Armstrong (AL/EAB) wrote:
> I'd like to optimize for 
> 
>   - compiling programs with a few hundred source code files
>   - making a high performance web server
> 
> Where is my money better spent?
> 
>    A cheapish processor with as much memory as possible 
>    Say a Athlon 64 3000+ 2GHz 512KB cache at 1295 kr
>    With 4 G memory (about 1000 kr/G)
> 
>    Or the cheapest dual core Athlon 64 X2 3800+ 2GH 1MB = 3250kr
>    With 2 G memory
> 
> In the old days I always said that buying more memory was better than
> buying a faster processor - is this still true? - also what
> is the effect of increasing the size of the processor cache contra
> more main memory for the same money?

For the sake of argument, suppose that the dual core would do everything twice
as fast (it certainly won't do better). This will not result in a 2x perceived
increase in performance, since most of the things that are being done twice as
fast took imperceptible time to begin with.

It is more effective to remove situations that cause pathologically bad
performance -- that is, performance so bad that just doubling the speed won't
fix it. One such situation is virtual memory thrashing. The 4G box will be
able to do more before running into this problem (and the 64-bit address
space allows you to actually make use of 4G).

-- 
David Hopwood <>




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