External Portable I/O
Personal computer users are creatures of habit as much as anyone else. Therefore, as they moved toward portable computers, they wanted the types of features they had come to expect from their larger desktops and towers. These features typically include an alphanumeric keyboard, a video display, and a pointing device.
Most portables offer standard connectors to enable full-size keyboards and VGA monitors to be plugged in. The VGA connector is usually the standard 15-pin D-shell type; the external keyboard connector is generally the 6-pin mini-DIN (PS/2) type. When an external keyboard is plugged in, the built-in keyboard is disabled. The portable's BIOS software permits the user to enable either or both displays while the external monitor is connected.
The standard I/O ports included in most notebook computers consist of a single parallel port, a single serial port, an external VGA monitor connector, an external keyboard connector, and a docking-port expansion bus. Some models are available with a second serial-port connector, but they are not common. In addition, most notebooks include a USB port and an infrared link.
Figure 3.12 shows the port connections associated with most portable systems. This example places the connectors on the back of the unit, just as they would be in a typical desktop. Other units may place some of these connectors along the sides of the unit instead. High-end portables may include an array of other connectors, such as external microphone and speaker jacks. Some connectors may be hidden behind hinged doors for protection. These doors normally snap closed.
Figure 3.12 Notebook back-panel connections.