Infrastructure-as-a-service lets companies focus on their core competencies without having to worry about buying, deploying, and maintaining data center hardware or facilities. IaaS is why Instagram sold at a $1 billion valuation with only 13 employees and why Pinterest served nearly 12 million monthly unique visitors with only 16 employees.

For our new Buyer's Guide, we defined an IaaS provider as offering self-service provisioning of an extremely large number of virtual machines and storage using an API or a Web control panel, without customers having to interact with an engineer or salesperson. For many companies, IaaS offers significant benefits, but with an ever-growing number of providers, it's difficult to know which will be the best choice. To help in the hunt for the perfect IaaS provider, we queried a dozen vendors about their offerings. Eight responded: GoGrid, Google, IBM, Internap, Joyent, NaviSite, SoftLayer, and Terremark. Amazon Web Services didn't respond, but given that it's a major IaaS player, we found answers to our questions on its website. We compared providers in several categories; get the full results at informationweek.com/ reports/iaasguide.

CPU And Memory

Most vendors offer a variety of VMs based on the number of CPU cores, amount of RAM, and amount of local storage that comes with each VM. There are lots of options, from half a core (GoGrid) to 24 cores (also GoGrid), and 256 MB of RAM (Terremark) to 68.4 GB of RAM (Amazon). However, because virtualization does not lend itself to exact CPU definitions, some IaaS vendors have created their own nomenclature for how much processing power comes with each core on a particular VM. Amazon defines an "Elastic Compute Unit," or ECU, as "the equivalent CPU capacity of a 1.0-1.2 GHz 2007 Opteron or 2007 Xeon processor." Google uses a "Google Compute Engine Unit," ...