Module 4

Peripheral Devices

Serial, Parallel, and PS/2 Facts

Interface

Serial Parallel Devices PS/2

Description

• Data is transmitted one bit at a time. • The maximum length for an RS-232 serial cable is 50 feet. • Serial devices use COM ports for system resources.

• Devices might cause a resource sharing problem. • To add serial ports to a computer, install an adapter card. • You should know the following facts about parallel devices: Data is transmitted 8 bits (one byte) at a time • Parallel devices use LPT ports for printers. • PS/2 adapters continue to be used for keyboards (purple) and mice (green).

USB

• • • • • • USB is a serial interface that supports low- and high-speed devices.

USB supports almost any kind of peripheral device, including keyboards, mice, scanners, digital cameras, printers, and storage devices. USB supports Plug-and-Play and hot swapping (adding and removing devices without rebooting--also known as hot plugging). USB allows 127 devices to be connected to a single computer (directly to the host or by hubs). All devices connected together share computer resources (IRQs, I/O addresses). The computer's BIOS must support USB and have USB enabled.

Firewire

• • • • • • Uses a serial bus using twisted-pair wiring for data transport. Lets you connect up to 63 devices on one IEEE 1394 bus. Supports many kinds of isochronous devices (devices requiring additional bandwidth to accommodate streaming data), such as digital video cameras and recorders, hard drives, and network adapters. Supports Plug-and-Play and hot-swapping (you can add and remove devices without rebooting). Can provide power (up to certain limits) to devices. Supports peer-to-peer transfers. For example, data can be transmitted between a digital video camera and a recording device without going through a computer.

Device Type

Keyboard Mouse Touchscreen KVM switch

Input Device

Considerations

Keyboards typically connect through a PS/2 or USB port. • A mouse typically connects through a PS/2 or USB port • Mechanical mice use a roller ball to detect motion. • Optical mice use light rays to detect motion.

• A trackball is a pointing device that is like an upside-down mechanical mouse where the user manipulates the pointer by rolling the ball. • A touchscreen is a special monitor that allows input by tapping or writing with a stylus or fingers. Touchscreens are used in kiosks and portable devices such as PDAs and Tablet PCs.

• A KVM (keyboard, video, mouse) switch allows you to connect multiple PCs to a single set of input/output devices.

CRT Monitor

Consideration Description

Screen size • Screen size is the diagonal measure of the display tube. Resolution Dot pitch The resolution is the number of pixels available on a display screen. Monitors that support a higher resolution can display higher-quality graphics or have a larger screen area.

The dot pitch is the distance between pixels measured in millimeters. The smaller the dot pitch, the more room there is for higher resolutions and the sharper a picture may be.

Refresh rate Interlacing The refresh rate is the amount of time required for the CRT's electron beam to paint the screen from top to bottom. Increasing the refresh rate reduces screen flicker. Refresh rates are measured in Hz. Interlacing is drawing the screen in two passes; odd lines on the first and then the even lines on the second pass. Non-interlaced monitors produce the least amount of flicker.

LCD Monitor

Factor

Display characteristics Backlight method Aspect ratio Resolution

Description

• The contrast ratio refers to the difference in light intensity between the brightest white and the darkest black. An example contrast ratio is 1000:1. A higher initial number indicates a better quality picture.

• The LCD backlight provides the light that makes the individual pixels visible. The light itself is actually along the top, bottom, and/or sides, with a special layer that reflects the light throughout the display. • The aspect ratio is the ratio of the width and the height. Normal displays have a 4:3 aspect ratio (used in CRT displays). • Widescreen displays have a 16:10 aspect ratio. • HDTV screens have a 16:9 aspect ratio. The resolution is the number of pixels, and is expressed using two numbers: the number of horizontal rows and vertical columns • VGA = 640 x 480, SVGA = 800 x 600, XGA = 1024 x 768

LCD Monitor

HDTV support Screen size • You can purchase an HDTV that can also function as a monitor, or a monitor that can function as a TV. Resolutions used by HDTV are: 1280 x 720 and 1920 x 1080 • An HDMI port accepts both video and audio input.

• Built-in speakers and audio-out to external speakers • Monitor size is typically described using a diagonal measurement using a single value for the screen size. LCD monitors can use the entire screen for displaying images. Because of the difference in effective viewing size, you can often purchase a smaller LCD monitor and get the equivalent viewing size of a larger CRT monitor. For example, you can replace a 19" CRT monitor with a 17" LCD monitor and have about the same effective viewing size.

Sound Card

• A sound card is an expansion card (or a component of the motherboard) that manages sound input and output. Because computers use digital data, sound cards must convert analog sound into digital data, and • • digital data into analog sound.

The Analog to Digital Converter (ADC) converts analog sound into digital data. The Digital Signal Processor (DSP) is an on-board processor that reduces the CPU load. The Digital to Analog Converter (DAC) converts digital data into analog sound (in preparation to be played on speakers).

Sound Card

• • • • • • • • Sound card drivers and other software save digital audio into several different file types. WAV (Windows standard), a widely used and compatible file type. AIFF (Audio Interchange File Format), the Macintosh equivalent of the WAV. AU (UNIX standard), supported by most Web browsers. MP3 (MPEG-1 Layer 3), a highly effective audio compression standard. AAC (Advanced Audio Coding), also known as MPEG-2, a compression expected to replace MP3. RA or RAM (Real Networks), developed for streaming audio files. Requires proprietary software. WMA (Windows Media Audio), a highly compatible standard developed to compete with Real Audio. MIDI, not a true audio file, but contains data to reproduce sounds through electronic synthesis.

Hardware Devices

Concept

System resources Plug and Play (PnP)

Description

• A computer assigns system resources to hardware devices, and the computer uses these assignments to communicate with the device.

• IRQ (Interrupt Request) is the method used by different system devices to interact with the CPU • DMA (Direct Memory Access) channels are conduits used by high speed devices to communicate directly with RAM, bypassing the CPU. • An I/O address (also known as a port address) allows two devices in a computer to send information to each other. • Newer systems use Plug and Play to automatically configure the resources used by each device. The device, the BIOS, and the operating system must support Plug and Play standards. • All new devices and operating systems are Plug and Play compatible.

Hardware Devices

Concept

Driver Hot swapping/ plugging

Description

• A driver is a type of program that enables the operating system to interact with hardware devices. Signed drivers are drivers that include a digital signature. The digital signature proves that: • The driver comes from the reported publisher. • The driver has not been altered or modified. • Drivers that have passed specific tests on Windows qualify for the Certified for Windows logo and are given a special digital signature. • Hot swappable devices are devices that can be added and removed without shutting down the computer by automatically detecting and configuring devices that are added. • Hot swapping must be supported by the BIOS, the bus type or controller, the device, and the driver/operating system. USB and Firewire devices are examples of buses designed specifically with hot swap support. • IDE drives are not hot swappable; some (most newer) SATA drives are hot swappable.

Device Installation

• • • • Before purchasing or installing the device, verify that the device is compatible with the version of Windows you are running by checking product documentation and Certified for Windows Logo. Obtain the latest driver before installation by checking the manufacturer's Web site for an updated driver. For Windows Vista, unsigned and self-signed drivers must be manually approved (Warn is the default and only setting). However, you cannot install unsigned drivers on x64 versions of Windows Vista. Driver signing options are on the Hardware tab of the System Properties. Click the Driver Signing button to modify the settings.

Device Installation

• • • Use Device Manager to view installed devices and their status. To open Device Manager: – Click Start, right-click My Computer and select Manage to open Computer Management. Select the Device Manager snap-in.

Use the device icon to identify the status of the device: – No icon: Windows did not detect the device. Try scanning for new hardware or rebooting the system to detect the device. – A normal icon means the device was configured, the appropriate driver was installed, and the device is working properly. – An icon with a yellow exclamation mark means the device was detected, but could not be configured properly. In this case, make sure you have the latest driver for the device. – An icon with a red X means the device is disabled.