You would think comparing the price of an hour's worth of computing among cloud vendors would be a simple task. But cloud pricing tables quickly make it clear that the suppliers are not all that interested in encouraging comparison shopping. Nor are there common measures or shared terminology that would help establish the comparison.
Each vendor preconfigures server templates with networking and storage, then offers server sizes that typically run from micro to small, medium, large and extra-large. But nowhere is there a clear definition of these terms. A small virtual server gets a stated amount of virtual CPU power, but the Amazon EC2 virtual CPU is different from the Rackspace, Microsoft Azure or Google Compute Engine virtual CPU. One vendor's virtual server is defined with less CPU but more storage than another's. Load balancing and data movement between virtual servers is free with one vendor, and incurs significant add-on charges with another.
Potential cloud consumers get help estimating what their needs might cost from individual vendors. But calculating a comparison of charges from one vendor to another remains very difficult. Amazon further complicates the picture by varying charges slightly based on where its data centers are located. Rackspace competes for entry-level customers; Microsoft competes for developer-oriented customers; Amazon competes on its head start in building infrastructure-as-a-service and years of in-house usage before launching its public EC2 service. Savvy shoppers understand where each vendor's most competitive offerings are and buy accordingly.