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What is the relation between CPU and RAM size.

 
Shreenath
Occasional Advisor

What is the relation between CPU and RAM size.

HI,
I have 2CPU windows machine. I wanted to upgrade to 4CPU. I wanted to know is there any relation/formula between number of CPU and RAM size. ie if i have 4CPU what is the min and max RAM size we can have. is there any link which gives the this figure.

I wanted to know for Unix machine also

Regards,
Shreenath
4 REPLIES 4
Dennis Handly
Acclaimed Contributor

Re: What is the relation between CPU and RAM size.

It depends on the application. You may want 10s of Gb for Oracle databases.
TTr
Honored Contributor

Re: What is the relation between CPU and RAM size.

You want to upgrade your CPUs because there are CPU issues? Then check the current memory utilization as well. If you add CPUs the process throughput of the server will increase (more processes will execute in same or less time because of the 4 CPUs). That means you will need more memory for the extra processes. There is no formula, use your judgement based on the current memory utilization. If it is high you should probably double on the memory as well. If it extremely low you may need some or none at all.

If you have a specific application environment, the vendor may provide some guidelines based on the number of concurrent users of the environment.
Emil Velez
Honored Contributor

Re: What is the relation between CPU and RAM size.


You solve a CPU problem by adding more CPUs (sometimes) you fix a memory shortage issue by adding memory. They are not related. You could have a single processor system with a memory problem and when you add memory response time is acceptable.

The major issue when you have a CPU problem is a run queue (load average). If it is high you have more threads that are "runable" than you have cpus to run them on.

The major issue you ahve when you have a memory problem is "free memory" less than 64 MB and/or Vhand is using CPU. IF you are that low on memory you have a memory problem. Now if you buffer cache is using memory set that lower first and see if you still have a memory problem.

IF you are in the GB or 100s of MB of free memory at all times you do not have a memory problem.

I hope this helps.
Peter Zeiszler
Trusted Contributor

Re: What is the relation between CPU and RAM size.

Are you thinking of doing virtualization and thinking of how much memory dedicated to each cpu?
If you are looking at upgrading do some trending performance monitoring of your CPU and Memory usage. Watch how much usage your pagefile system is using.