B.EXTERNAL CONNECTIONS

The oldest external connections used by computers were the serial and parallel ports. These were included on the original IBM PC from 1981. Originally designed as an interface to connect computer to computer, the serial port was eventually used with various devices, including modems, mice, keyboards, scanners, and some types of printers. Parallel ports were mainly used with printers, but some scanners and external drives used the parallel port.

The Universal Serial Bus (USB) interface was developed to replace both the serial and parallel ports as the standard for connecting external devices. Developed by a group of companies including Microsoft, Intel, and IBM, the USB standard was first introduced in 1995. Besides transferring data to and from the computer, USB can also provide a small amount of power, eliminating the need for external power cables for most peripherals. The USB 2.0 standard, which came into general usage in 2002, drastically improved the data transfer rate.

A competing standard to USB was developed at the same time by Apple and Texas Instruments. Officially called IEEE 1394, it is more commonly called FireWire. It is capable of transferring data at a higher rate than the original USB standard and became the standard interface for multimedia hardware, such as video cameras. But Apple’s royalty rate and the introduction of USB 2.0—as well as the fact that Intel, one of the companies behind USB, is responsible for most motherboards and chipsets in use—meant that FireWire was unlikely to become the standard peripheral interface for PCs. Today most computers have both USB and FireWire ports connected to the motherboard.

Wireless devices have also become commonplace with computers. The initial wireless interface used was infrared (IR), the same technology used in remote controls. However, this interface required that the device have a direct line of sight to the IR sensor so that the data could be transferred. It also had a high power requirement. Most modern wireless devices use radio frequency (RF) signals to communicate to the computer. One of the most common wireless standards used today is Bluetooth. It uses the same frequencies as the Wi-Fi standard used for wireless LANs.