Controlling the power state of a computer based on the value of a net useful activity metric

In a computer implemented method of controlling the power state of a computer, the total value of at least one activity metric of the computer is periodically determined, e.g. total CPU activity in a time slot (fig. 6). The accumulated contribution to the total value of one or more predetermined activities is determined and subtracted from the total value to provide a respective net value. The net value is compared S5 with respective preset threshold values and the power state of the computer is controlled S9, S11, S4 in dependence on the comparison. A data set held in a data store may be used to identify the one or more predetermined activities. An activity metric may be CPU activity or a value of input/output activity and the predetermined activities may be processes. An activity metric may be the number of active network connections or the number of logons.