Kate's Comment

One of the areas on which we reached clear agreement in the G-Cloud and App Store phase 2 was the definition the layers of the stack, infrastructure, platform and software, and their corresponding scalable, standardised counterparts: infrastructure as a service (IaaS), platform as a service (PaaS) and software as a service (SaaS). Pleasingly, our delinations were very similar to prior work from two decades ago by IBM, except that ours incorporate virtualisation.

Over the last two years there has been a lot of debate about what the embedded energy of a PC or server is compared with how much power it uses. I have crunched the numbers and believe that the figure for a server is about 1,000,000 Watt-hours (1MWh). Here is how I worked it out, and why it means that you should sweat the desktops but replace the servers.