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CPU / RAM relation

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CPU / RAM relation

Could anyone inform me whether a relation exists between the number of CPU's and the amount of memory required? A SA told me that a recent UNIX (AIX) server behaves most optimally with 1 GB of RAM per processor. For a 4 CPU box he recommended 4 GB RAM.
Does such a relation exists?

Thank you
6 REPLIES
Pete Randall
Outstanding Contributor
Solution

Re: CPU / RAM relation

RAM is primarily used as a cache, either to avoid swapping or I/O. In any situation, more RAM is good, but it's also expensive so you want to have a better idea what you really need before you run out and buy RAM based on some rule of thumb. Heavily loaded Database servers generally run best with 8GB or more, but if you're not running a big DB then that much RAM would be wasteful.

I know of no such relation specifically for CPU vs RAM. You really need to have a much better idea of your requirements.


Pete

Pete
Stefan Farrelly
Honored Contributor

Re: CPU / RAM relation

There is no relation between cpu and ram - god knows where your AIX SA dreamt that up from.

It entirely depends on your application. Weve got cpu intensive applications that need several cpu's and only 2Gb of ram, and others with only a couple of cpu's but several Gb of RAM. Whoever is supplying your application ask them how much ram it needs (depending on how many users etc.)
Im from Palmerston North, New Zealand, but somehow ended up in London...
John Palmer
Honored Contributor

Re: CPU / RAM relation

No it doesn't! It depends entirely on your application.

A CPU intensive app may not require a lot of memory and something that needs a lot of memory may not require a lot of CPU.

That said more memory is always better but you shouldn't pay out for something you don't need.

Regards,
John
Graham Cameron_1
Honored Contributor

Re: CPU / RAM relation

Is this a wind up ?

No such relation exists and it depends entirely on what you are doing.

A simple file server streaming files from disk can get away with relatively low amounts of memory, a greedy database like Oracle needs loads.

What your SA (what's an SA ?) says may be the recommended minimum, but I never heard of a server slowing down because it contained more than the 'optimal' amount of memory...

-- Graham
Computers make it easier to do a lot of things, but most of the things they make it easier to do don't need to be done.
Hein van den Heuvel
Honored Contributor

Re: CPU / RAM relation


As per other replies... it all depends!

Nevertheless, having said that, it is not a bad starting point if you have nothing else to go on at first.

Now assuming there is any value in a generic GB/cpu guideling, then for a recent commercial system I would suggest that 1GB is the bare minimum, 2GB often required and 4GB perhaps in the diminishing (sp?) return space.

(2 years ago I would have said 512mb/1/2
In a year I'll probably recommend 2/4/8 :-)

Hein.

SA = Solution Architect

Re: CPU / RAM relation

Thank you all. It confirms my thoughts on the subject. We can close this discussion for as far as I'm concerned.

By the way, SA is an acronym for System Administrator. Sorry for that.

Denys