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its face that detects the location and duration of contact, usually by a finger or stylus. All touch screens then supply this contact information to the PC as though it were a click event from a mouse. Touch screens are used in situations for which conventional mouse/keyboard input is either impossible or impractical. Here are a few places you’ll see touch screens at work:

Information kiosks

PDAs

Point of sale systems

Tablet PCs

Touch screens can be separated into two groups: built-in screens like the ones in PDAs, and standalone touch screen monitors like those used in many point of sale systems. From a technician’s standpoint, you can think of a standalone touch screen as a monitor with a built-in mouse. All touch screens have a separate USB or PS/2 port for the “mouse” part of the device, along with drivers you install just as you would for any USB mouse.

KVM Switches

A keyboard, video, mouse (KVM) switch is a hardware device that most commonly enables multiple computers to be viewed and controlled by a single mouse, keyboard, and screen. Some KVMs reverse that capability, enabling a single computer to be controlled by multiple keyboards, mice, or other devices. KVMs are especially useful in data centers where multiple servers are rack mounted, space is limited, and power is a concern. An administrator can use a single KVM to control multiple server systems from a single keyboard, mouse, and monitor.

There are many brands and types of KVM switches. Some enable you to connect to only two systems, and some support hundreds. Some even come with audio output jacks to support speakers. Typical KVMs come with two or more sets of wires that are used for input devices such as PS/2 and/or USB mice and video output (Figure 18-46).

Figure 18-46 A typical KVM switch

To use a KVM, you simply connect a keyboard, mouse, and monitor to the KVM and then connect the KVM to the desired computers. Once connected and properly configured, assigned keyboard hotkeys—a combination of keys typically assigned by the KVM manufacturer—enable you to toggle between the computers connected to the KVM. In most cases, you simply tap the Scroll Lock key twice to switch between sessions.

Installing a KVM is not difficult; the most important point to remember is to connect the individual sets of cables between the KVM ports and each computer one at a time, keeping track of which keyboard, mouse, and video cable go to which computers. (I highly recommend labeling and using twist or zip-ties.)

If you get the connections wrong, the KVM won’t function as desired. If you connect a mouse and keyboard wires to the correct KVM port, for example, but attach the same computer’s video cable to a different port on the KVM, you won’t get the correct video when you try to switch to that computer. The same holds true for the mouse and keyboard cables. Don’t cross the cables!

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NOTE Older KVMs are said to be passive, meaning they don’t continuously communicate with all connected systems. This can cause problems if the connected systems automatically reboot after a power surge or loss. Modern day active KVMs resolve this issue through peripheral emulation, meaning they communicate with and monitor all systems connected to the KVM.

Chapter Review

Questions

1. A serial port receives and sends serial data. What device translates that serial data into parallel data for the computer to use?

A. Parallel translator chip

B. Serial translator chip

C. COM chip

D. UART chip

2. What integrated circuit device controls USB devices connected to a USB port?

A. Host controller

B. IC-USB

C. Serial port

D. UART

3. What happens to bus speed and power usage when you plug multiple devices into a USB hub?

A. The bus speed stays constant, but power usage increases.

B. The bus speed increases because each device brings a little burst; power usage increases.

C. The bus speed decreases because all devices share the same total bandwidth; power usage increases.

D. The bus speed decreases because all devices