3.1.2 Device Controllers L/O units typically consist of a mechanical component and a electronic component. It is often possible to separate the two portions to provide a more modular and general design. The electronic component is called the device controller or adapter. On personal computers, it often takes the form of a printed circuit card that can be inserted into a expansion slot. The mechanical component is the device itself. This arrangement is shown in Fig. 3-2 into which a cable leading to The controller card usually has a connector on it can handle two, four, or even the device itself can be plugged. Many controllers eight identical devices. If the interface between the controller and device is a standard interface, either an official ANSI, IEEE, or Iso standard or a de facto one, then companies can make controllers or devices that fit that interface. Many companies, for example, make disk drives that match the IDE(integrated Drive
Electronics) and SCSI(Small Computer System Interface) interfaces.