PC Repair and Maintenance: A Practical Guide (Charles River Media Networking/Security)

Ports (Input/Output, or I/O) Overview

Ports, for the purpose of this chapter, are physical connectors and their corresponding software that conduct signals into and out of computers. Figure 3.23 shows the most common ports, and some are described in the upcoming list. These are often built into the motherboard, but are also on expansion cards.

Figure 3.23: Common ports.

Serial: 9-pin serial ports carry electrical pulses one at a time and therefore tend to be slow. They are used for older pointing devices (mice), connections to UPSs, Personal Data Devices (PDAs), digital cameras, and external modems. Serial ports are associated with software COM ports (see the Device Manager discussion in Chapter 2). Serial devices can be plugged in and unplugged without risking damage to the device or the computer.

Parallel: Used mostly for printers and scanners, 25-pin parallel ports carry eight electrical signals at one time. Associated with LPT ports in Device Manager and printer software, parallel devices can be plugged in and unplugged without risking damage to the device or the computer.

Universal Serial Bus (USB): USB ports are very versatile. Unlike serial and parallel devices, which require a separate IRQ per device, USB ports can be expanded through the use of USB hubs (adapters that convert one USB port to several), yet all devices connected to a single USB port on the computer safely share one IRQ. USB 2.0 is a newer standard for faster USB devices. Most USB 2.0 devices run if connected to older USB 1.1 ports, although they will be limited to the speed of the slower port. USB 1.0 devices work normally in USB 2.0 ports. Additionally, USB provides power to devices that don't use a lot of it. Another advantage to USB is that it is hot-pluggable or hot-swappable, meaning that devices can be plugged in and removed while powered on, without risking damage to the device or the computer. Although later versions of Windows 95 might support USB, most USB devices don't support Windows 95.

Video Graphics Adapter (VGA) ports: VGA is the standard for all analog monitors used since the early 1990s. VGA connectors have 15 pins and can be plugged and unplugged without risk of damage.

DVI ports: These are for digital monitors and also can be plugged and unplugged without risk of damage.

FireWire (IEEE 1394): Similar to USB, but much faster than USB 1.1. Used for all the types of peripherals as USB, plus digital audio and video cameras and other devices that require high-speed data transfer.

PS/2: Mouse and keyboard connectors. Plug and unplug only with computer power off.

DIN AT keyboard connectors: Used in older PCs.

PCMCIA (PC Card): Used almost exclusively in laptops, these are used mainly for modems, network adapters, and for tiny hard drives. These cards can usually be inserted in their slots without any special steps, but they should be stopped in Windows Control Panel, PCMCIA or PC Card applet before removing to prevent Windows problems such as lockups, or possible damage to the card.

Game Controller/MIDI port: These are 15-pin ports used for older game controllers and MIDI musical instrument devices.

SCSI (pronounced scuzzy): There are no fewer than seven different types of SCSI connectors, so chances are good that if you see a connector not covered here, it's a SCSI.

RJ-45 (Ethernet): This is a connector for a network cable.