Separation of memory oriented process and CPU oriented process

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http://serverfault.com – I am develops guy working for an e-commerce company I am running my e-commerce application built using ruby on rails spree commerce. I am presently running 2 medium instances in the production. One is a high memory instance which has 3.8 RAM and single Core CPU and another one is high CPU instance which has Dual Core CPU. Basically AWS calls it has m1.medium and c1.medium instance respectively. My question is it possible to separate the processes according the cpu intense and memory intense? So that all the cpu intense process can be made run in high cpu instance and all the memory intense pro (HowTos)