Table 1-12 Power Fluctuations
| Power Condition | Description |
| Blackout | Power failure |
| Brownout | Too little voltage |
| Sag | Very brief time (milliseconds) of too little voltage |
| Surge | Too much voltage |
| Spike | Very brief time (milliseconds) of too much voltage |
Table 1-13 describes solutions to the previous power issues.
Table 1-13 Power-Protection Devices
| Device | Description |
| Surge suppressor | Multiple plugs. |
| Protects against too much voltage. | |
| Note that power strips and standard multiplugs do not offer such | |
| protection. Make sure the device is marked as a surge suppressor | |
| and has a joule rating over 1000. | |
| Line conditioner | Cleans and smoothes the AC power signal. |
| Standby power supply | An SPS is usually a battery backup to the computer that is |
| (SPS) | recharged by the wall outlet and takes over from AC power in the |
| event of an AC power failure. This type of battery backup is gener- | |
| ally referred to as a UPS, although a true UPS is different. | |
| Uninterruptible power | Properly understood, a UPS is a backup power supply (usu- |
| supply (UPS) | ally a battery) that continuously provides power to the computer. |
| However, this term is also used to refer to devices that switch from | |
| AC to battery in the event of failure (SPS). | |
| Both SPS and UPS unit capacities are measured by the volt-amp | |
| (VA) rating. | |
Chapter 1: Hardware 33
Monitors and Display Resolutions
Contrast ratio is the comparison of the brightest to the darkest color a monitor can create. The higher the ratio, the more brightness variation exists in the monitor.
Video cards have a basic resolution, usually 640x480 or 800x600, with 256 colors. If the PC boots to this reduced resolution and limited color scheme and was not started in Safe mode, it needs a better video driver. Table 1-14 shows the resolutions you need to know for the A+ exams.
Table 1-14 Monitor Resolutions
| Name | X Pixels Wide | Y Pixels Tall | Aspect Ratio |
| VGA | 4:3 (1.33:1) | ||
| SVGA | 4:3 (1.33:1) | ||
| XGA | 4:3 (1.33:1) | ||
| XGA+ | 4:3 (1.33:1) | ||
| WXGA | 16:9 | ||
| SXGA | 4:3 (1.33:1) | ||
| SXGA+ | 4:3 (1.33:1) | ||
| UXGA | 4:3 (1.33:1) | ||
| WUXGA | 16:9 | ||
| QXGA | 4:3 (1.33:1) | ||
There are many additional resolutions, and most LCD or LED displays now support 16:9 (or in some cases 16:10) aspect ratios.
CRTs
Warning: Do not open cathode ray tubes (CRT). They are field replaceable units (FRU). In other words, replace CRTs. Do not fix them. They contain capacitors that can shock you long after they are unplugged. Before sending CRTs to a recycler for disposal, the capacitors should be discharged by touching and connecting the phase with the ground plug and then the neutral to the ground plug with an insulated screwdriver or pliers.
A CRT monitor has many manual adjustments that should all be set to “middle” level. A beam sweeps sideways lines down the entire length of the screen 60 to 100 times a second; this is referred to as the vertical refresh rate, and is measured in Hertz (Hz). The width and height of the picture is controlled by controls vertical and horizontal, respectively. Contrast and brightness
should also be set for a middle setting. Contrast controls the ratio of the brightest and darkest light. Brightness controls the overall intensity of the display. They are physically measured diagonally. A 17-inch display means that the picture tube has this dimension when measured from diagonal corners; actual viewing area might be as much as 1 inch less. Interlacing draws the odd-numbered
34 CompTIA A+ Quick Reference
rows of each frame, and then one-sixtieth of a second later, fills the space with the even numbered rows.
Note that if you use a CRT at different resolutions or different refresh rates, you must adjust the picture the first time you use the new setting. NVRAM inside the CRT stores settings for reuse.
LCDs
Liquid crystal display (LCD) monitors have almost completely replaced large, heavy CRT moni-tors. LCD monitors are illuminated in several different ways: a flat florescent tube; a panel of LEDs; or in the case of LCD projectors, a bright bulb. LED backlighting offers more clarity, is thinner, and is more rugged than the florescent. Typically, LCD displays that use LED backlighting are referred to as LED or LCD-LED displays, and sometimes LCD displays with fluorescent back-lighting are known as LCD-CCFL displays.
Passive matrix LCD monitors have chips that control the vertical and horizontal sets of wires. When a pixel is charged by both chips, it turns on. Active matrix monitors act like one big inte-grated circuit with a transistor for each group of three subpixels (red, green, and blue). Each group of subpixels equals a pixel.
After the correct drivers are installed, an LCD screen should be run in its native mode for best results.
Other Display Devices
Other common display devices include data projectors and HDTVs.
Data projectors use one of two technologies: LCD or digital light processing (DLP). LCD projec-tors use three separate LCDs, one each for red, green, and blue light, along with a series of dichro-ic mirrors to reflect colors to each LCD. Before projection, the images are combined together. DLP uses an array of micromirrors on a specialized processing chip that reflect light either onto the screen or away, in much the same way optical drives read their media. A color wheel spinning at high speed works with the micromirror array to create full-motion color images.
HDTVs might use LCD with fluorescent backlighting, LCD with LED backlighting (commonly known as LED), DLP, or plasma screen technologies and are interfaced to a computer through VGA, DVI-D, HDMI, or DisplayPort connectors. HDTVs can be used as primary or additional displays.
Display Connectors
VGA, DVI-D, and HDMI are the most common types of video connectors used for monitors or projectors. Some video cards or systems with VGA ports also have S-video or composite ports for use with standard TVs and other devices that don’t support HDTV resolutions. DVI-D, HDMI, and DisplayPort are all digital standards.
Chapter 1: Hardware 35
Multiple Displays
It is not uncommon to have multiple monitors on one PC. The most common case of this is a lap-top paired with a projector. Function keys toggle among settings that mirror the display, extend the display from the main screen onto the projector, or run the projector exclusively and shut off the main screen. Workstation and gaming PCs commonly have two or more monitors usually set up as a continuation from one to the next. The display settings in the Control Panel provide more control and support for multiple monitors. Projectors and HDTVs are managed by Windows using the same Display properties sheets used by conventional CRT or LCD displays.
I/O Devices
Most input/output devices connect to a PC via a USB port. Even wireless devices ultimately ter-minate at the PC through a USB port. A USB device is a plug-and-play device if its drivers are already installed in Windows. However, you should install the drivers for a new device before connecting it to your computer for the first time. The other major plug-and-play interface is IEEE-1394 (FireWire). Older I/O devices that use parallel (LPT), serial (RS-232), or PS/2 ports cannot be connected when the computer is running.
All I/O devices require drivers. Drivers are instructions to teach the OS how to use and communi-cate with a new piece of hardware. They are normally stored on CDs that come with the device, but they can also be downloaded from the manufacturer’s website. Often, drivers are included in the OS for commonly used devices, such as mice, keyboards, USB storage, and many printers.
Mice and Keyboards
Optical mice use an LED or laser to illuminate the area directly beneath the mouse and a motion-sensing technology to determine the direction and speed of that surface as the mouse moves. Ball mice use a ball that roles on two rollers mounted perpendicular to each other. One measures move-ment along the Y axis, and the other on the X axis.
A few desktop keyboards include a mouse-equivalent pointing stick (originally developed by IBM as the TrackPoint II); however, nearly all laptop keyboards include a mouse-equivalent touch pad (and a few also have pointing sticks). Users who dislike touch pads or pointing sticks can use a mouse instead.
Speakers and Microphones
The audio port uses a headphone jack. The formal name for this port is a mini-DIN Tip Sleeve Ring (TSR) 3.5mm jack. This makes the audio port compatible with standard stereo equipment. A higher-quality audio connection splits the signal into component signals. Dolby 5.1 uses five signals, each to a dedicated speaker (the .1 refers to a subwoofer, used for very low sounds). These are analog signals, which means that the sound card is responsible for digital-to-audio conversion (DAC). 7.1 audio uses seven dedicated speakers plus a subwoofer. Sony/Phillips Digital Interface Format (SPDIF) sends a digital signal over a fiber-optic line or coaxial cable to the speakers where it is decoded and converted to an analog signal and, ultimately, an audible sound.
36 CompTIA A+ Quick Reference
Microphones are essentially speakers in reverse. The diaphragm moves in response to sound waves. That signal is converted into a digital signal inside the sound card. Note that the standard PC99 color-coding for audio uses pink for the microphone port, blue for line in like a stereo or iPod, and the green color is audio out for speakers and headphones. These are de facto standards and are, therefore, not consistent among all manufacturers.
Video-Input Devices
Still image, video, and webcams work on the same basic principal. A charged coupled device (CCD) or CMOS converts a visual input into a binary stream through an analog-to-digital conversion (ADC). A significant difference is the way in which the camera transfers that image to the PC.
With standalone video cameras (camcorders and digital cameras), video and pictures are often stored as files that are transferred to the PC, such as a USB flash drive through a USB, FireWire port, or Bluetooth connection. In streaming video environments (security cameras, TV, and movie production), the ADC can take place in the camera and stream a digital signal through a USB or FireWire port.
Older types of video cameras don’t stream a digital signal. Instead, it sends an analog signal through RCA, S-video, network interfaces, or proprietary ports. In this case, the ADC takes place in a video capture card.
Once on the PC, the video must either be stored or viewed in real time or both. Applications such as video-editing software manipulate the raw video, much like a word processor can open, edit, and save a document.
Other I/O Devices
Some devices require additional applications to work properly. Biometric devices combine an input device with an application that compares a unique pattern (retina, fingerprint, palm print, and so on) to a password. That password is then used to gain access to the operating system or file. Touch screens are an input device that maps the coordinates of the touch location to an application that translates that into executable commands or files. Barcode readers shine a laser on a black-and-white barcode. The laser reflects the pattern to a sensor and reads the code. That code is compared to a database, and the associated item or file is accessed.