Publisher Summary This chapter discusses software issues relating to analog-to-digital conversions and digital-to-analog conversions. Natural parameters such as temperature, pressure, displacement, altitude, humidity, and flow are analog. The value taken by the parameters can change continuously instead of in discrete steps. To be manipulated by a computer, these analog parameters must be converted to digital. This process is referred to as analog-to-digital conversion. Certain analog parameters can also be controlled. For example, the speed of an automobile is adjusted by changing the position of the throttle. The exact position of the throttle depends on many factors, such as wind resistance and whether one is going uphill or downhill. One can control the flow of liquids or gases by adjusting the opening of a valve. Voice coil type actuators control the position of the heads in some hard disk drives. An actuator is a device that converts electrical or pneumatic signals into linear motion. To be controlled by a computer, analog parameters must be converted from their digital form to analog. This process is referred to as digital-to-analog conversion.