 With current technology, most modern computers keep track of local civil time, as do many other household and personal devices such as VCRs, DVRs, cable TV receivers, PDAs, pagers, cell phones, fax machines, telephone answering machines, cameras, camcorders, central air conditioners, and microwave ovens.Microcontrollers operating within embedded systems (such as the Raspberry Pi, Arduino, and other similar systems) do not always have internal hardware to keep track of time.Many such controller systems operate without knowledge of the external time.