Software causes computers to consume energy but how much energy should they use? Have you ever wished that the battery in your laptop, tablet, or mobile phone would last longer than it does? Wouldn’t it be great if your business could save money on the electricity required to cool the data center? Much of computer energy used (and saved) is based on the effectiveness of hardware energy-efficiency and the hardware power states of your computer. Software has an impact as well, in two ways: while running a “workload” and while “idle.” This paper looks at the energy-efficiency of software running a “workload”.