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I/O Ports and Devices

This chapter is from the book

This chapter is from the book

Understanding Input Devices

Modern PCs use many different types of input devices, including keyboards and mice, bar code readers, biometric devices, and touch screens. The following sections cover the important characteristics of each of these devices.


The keyboard remains the primary method used to send commands to the computer and enter data. You can even use it to maneuver around the Windows Desktop if your mouse or other pointing device stops working.

Keyboards can be connected through dedicated keyboard connectors or through the USB port. Extremely old systems use the 5-pin DIN connector, whereas newer systems use the smaller 6-pin mini-DIN connector (also called the PS/2 keyboard connector) shown in Figure 3-1.

Most recent systems use the USB port for the keyboard, and any system with USB ports can be equipped with a USB keyboard if the system BIOS supports USB Legacy mode and if the system runs an operating system that supports USB ports (Windows 98 or newer).

Most recent systems use the 104-key keyboard layout, which includes Windows keys on each side of the space bar and a right-click key next to the right Ctrl key. Otherwise, the standard 104-key keyboard's layout is the same as the older standard 101-key keyboard.

Mouse and Pointing Devices

Next to the keyboard, the mouse is the most important device used to send commands to the computer. For Windows users who don't perform data entry, the mouse is even more important than the keyboard. Mouse alternatives, such as trackballs or touchpads, are considered mouse devices because they install and are configured the same way.

Current mice and pointing devices use the USB 1.1 or USB 2.0 port, but older models used the 6-pin PS/2 (mini-DIN), serial (COM) ports, or 8-pin bus mouse port.

Some mice sold at retail work with either the USB port or the PS/2 port and include a PS/2 adapter. This adapter and others are shown in Figure 3-16.

Figure 3-16

Figure 3-16 A USB keyboard–to–PS/2 keyboard port adapter (top) compared to a USB mouse–to–PS/2 mouse port adapter (middle) and serial mouse–to–PS/2 mouse port adapter (bottom).

A USB mouse uses the IRQ and I/O port address of the USB port to which it is connected. Because a single USB port can support up to 127 devices through the use of hubs, a USB mouse doesn't tie up hardware resources the way other mouse types do.

A PS/2 mouse uses IRQ 12; if IRQ 12 is not available, the device using that IRQ must be moved to another IRQ to enable IRQ 12 to be used by the mouse. A serial mouse uses the IRQ and I/O port address of the serial port to which it is connected.

Game Controllers

Game controllers are handheld devices that provide input to computer games and other applications. They are most common in gaming consoles but can also be connected to PCs by way of a USB or 15-pin parallel connector, often found on soundcards.

The most common type of game controller is the game pad, which is held with both hands and is manipulated by a person's fingers and thumbs. Many computer games are developed to work with gamepads, but some games require the use of a keyboard and mouse. On the other side of the spectrum, applications such as browsers can often be manipulated by gamepads. This all depends on application support, and the programming strength of the gamepad driver software.

Bar Code Reader

Bar code readers are used in a variety of point-of-sale retail, library, industrial, medical, and other environments to track inventory.

Bar code readers use one of the following technologies:

  • Pen-based readers—Use a pen-shaped device that includes a light source and photo diode in the tip. The point of the pen is dragged across the bar code to read the varying thicknesses and positions of the bars in the bar code and translate them into a digitized code that is transmitted to the POS or inventory system.
  • Laser scanners—Commonly used in grocery and mass-market stores. They use a horizontal-mounted or vertical-mounted prism or mirror and laser beam protected by a transparent glass cover to read bar codes.
  • Charge-coupled device (CCD) readers—Use a hand-held gun-shaped device to hold an array of light sensors mounted in a row. The reader emits light that is reflected off the bar code and is detected by the light sensors.
  • Camera-based readers—Contain many rows of CCD sensors that generate an image of the sensor that is processed to decode the barcode information.

Biometric Devices

A biometric device is used to prevent access to a computer or other electronic device by anyone other than the authorized user. It does so by comparing the fingerprint or other biometric marker of the prospective user to the information stored by the authorized user during initial setup. Some keyboards and laptop computers include built-in fingerprint readers, and some vendors also produce USB-based fingerprint readers.

To learn more about fingerprint readers and other biometric devices, see Chapter 9, "Basic Security."

Voice-Activated Typing

For those who want to dictate documents instead of typing them and issue commands to the computer by voice instead of with the keyboard and mouse, voice-activated typing is a viable alternative. Also known as voice-to-text recognition software, voice recognition, and dictation software, these programs take a person's speech and interpret it to the computer. This can manifest itself as the automatic display of words in a Microsoft Word document, or as the control of a browser and other applications, even the operating system.

For the voice-activated typist, a few items are necessary, including software (a commonly used program is Dragon Naturally Speaking), a headset with microphone, and a fairly powerful computer (due to the fact that most of these programs are quite resource intensive).

The user first needs to train the software with their speaking style. Afterward, the user's inflection, and other nuances, are stored in a user profile. The more a person uses software such as this, the better the software will be able to recognize the user's words and commands. User profiles can be moved from one computer to another as long as the other computer has the same voice-activated software installed.

Organizations that want to implement voice-activated typing software should look for a solution that meets the Americans with Disability Act (ADA) requirements. This ensures that everyone in the organization who wants to use the software can do so easily and efficiently.

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