Introduction to Ports

Most computers have at least one kind of port for connecting peripheral devices. Traditionally, most equipment employs a wired connection, although recent technology may also offer you the option of a wireless connection.

Modern Wired Ports

Modern computers have at least one serial interface, where the data bits are conveyed one after the other along the same wires. Although older serial ports are slower than a parallel port (see below), most recent serial interfaces are very fast.

The most common serial interfaces are Universal Serial Bus (USB) and FireWire. USB, when in the form of USB 1.0, is really limited to non-demanding devices, such as a printer, scanner, modem or a modest backup drive, although USB 2.0 is perfectly capable of working with faster drives. FireWire, on the other hand, is designed specifically for high-speed connections, making it particularly suitable for digital video transfers or for connecting a fast disk drive.

Creating a Serial Bus

USB and FireWire ports operate as a bus, allowing several devices to be connected at once. This kind of plug and play interface allows hot-plugging, meaning that you can connect or disconnect any device, powered or not, without harming your hardware or software. Connections are sometimes made in the form of a daisy chain, as shown below:-

Although this can create a network, it’s really intended for connecting several devices to your machine. If you have numerous items, or some lack the necessary sockets for daisy-chaining, you can use a suitable hub, wired as shown below:-

The Apple Desktop Bus (ADB), as fitted to older Mac OS computers, also allows several devices, such as a keyboard, mouse or modem, to be connected at once, as shown here:-

Wireless Ports

A wireless connection, usually radio-based, lets you use your equipment without having to worry about plugs and cables, although you must ensure that your devices are within range of each other. The most common system is Bluetooth, which can be built into the computer itself or accommodated by a Bluetooth adaptor that you plug into a spare USB port.

Traditional Serial Ports

Older computers frequently incorporate an earlier generation of wired serial ports that are based on the RS-232 and RS-422 standards. Unlike USB or FireWire, these interfaces can only serve one device at a time. This means that you must use a point-to-point connection to connect every device, as in this example, where a printer is linked to a computer:-

To use several devices you must fit a manually-operated serial port switch box or serial port expander, the latter using software to fool the computer into seeing only one device at a time. The box or port expander is connected as shown here:-

Parallel Ports

Older wired ports, such as the Small Computer System Interface (SCSI) and the Centronics printer port on a PC, are parallel interfaces. These have separate wires for each data bit, requiring a multiway cable and cumbersome connectors.

Parallel ports, which are usually very fast, can be connected to several items at once so as to create a bus. Unlike modern serial ports, however, the data circuits are wired directly across each device, ensuring a fast transfer of information. Complications can arise with SCSI, however, where each device must be given a device ID. In addition, one or more terminators may have to be plugged across the interface at various points in the wiring to ensure a reliable transfer of data.

©Ray White 2004.