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THE COMPUTER SYSTEM UNIT, SYSTEM SOFTWARE'S AND OPERATING SYSTEM

System unit (system cabinet or chassis) contains electronic components.
Four basic types are:
desktop (tower models positioned vertically),
notebook,
tablet PC (convertible and slate), and
handheld PDA (personal digital assistant) most widely used handheld computer.
System unit (system cabinet or chassis) contains electronic components.
Four basic types are:
desktop (tower models positioned vertically),
notebook,
tablet PC (convertible and slate), and
handheld PDA (personal digital assistant) most widely used handheld computer.
The System board (main board or mother-board) connects all system components and allows input and output devices to communicate with the system unit. It is a flat circuit board covered with electronic components:
Sockets provide connection points for chips (silicon chips, semiconductors, integrated circuits). Chips mounted on carrier packages.
Slots provide connection points for specialized cards or circuit boards.
Connecting lines (bus lines) provide pathways to support communication.
The microprocessor is a single chip that contains the central processing unit (CPU) or processor. It has two basic components: control unit and arithmetic-logic unit (ALU).
Microprocessor Chips
A word is the number of bits that can be accessed by the microprocessor at one time. Older microprocessors process data and instructions in microseconds; newer ones in nanoseconds.
Complex instruction set computer (CISC) and reduced instruction set computer (RISC) chips are two different designs. RISC chips used in powerful microcomputers known as work-stations.
Memory holds data, instructions, and information. There are three types of memory chips:
RAM (random access memory) chips are volatile storage. Programs and data are stored in RAM memory addresses
ROM (read only memory) chips, also called firmware, are nonvolatile storage and control essential system operations.
CMOS (complementary metal-oxide semiconductor) provides flexibility for a computer
Computers with closed architecture are not easily expanded. Open architecture computers typically have slots on their system boards to accept expansion cards (plug-in boards, controller cards, adapter cards, or interface cards).
Expansion of expansion cards include:
Video cards- also known as graphics cards, connect to monitors.
Sound cards- connect to speakers.
Modem cards- also known as internal modems, connect over telephone lines.
Network interface cards (NIC)- also known as network adaptor cards, connect to a network.

TV tuner cards- contain TV tuner and video capture capabilities, also known as television boards and personal video recorder cards.

PC cards- credit card-size expansion cards for portable computers, also known as PCMCIA (Personal Computer Memory Card International Association) cards. Three types are Type I, II and III.

Plug and Play is a set of hardware and software standards designed to assist with the installation of expansion cards.
For standard ports are:
. Serial ~ send data one bit at a time.
. Parallel ~ send eight bits simultaneously.
. USB (universal serial bus) ~ faster, one port can connect several devices to system unit.
. Fire wire (HPSB or high performance serial bus) ~ as far as USB 2.0 ports; provide connection for specialized fire wire devices.
For Specialized Ports
MIDI (musical instrument interface) ~ special ports for musical instrument such as electronic keyboards. Synthesizers converts MIDI instructions to music .
SCSI (small computer interface) ~ high speed parallel port for connecting multiple devices to a single SCSI card.
IrDA (infrared data association) ~known as also fast infrared (FIR) ports providing wireless connections.
System software works with end users, application programs, and computer hardware to handle many details relating to computer operations.
Not a single program but a collection or system of programs. These programs handle hundreds of technical details with little or no user intervention.
Four kinds of systems programs are operating systems, utilities, device drivers, and language translators.
Operating systems coordinate resources, provide an interface between users and the computer, and run programs.
Utilities (service programs) perform specific tasks related to managing computer resources.
Device drivers allow particular input or output devices to communicate with the rest of the computer system.
Language translators convert programming instructions written by programmers into a language that computers can understand and process.
Operating systems, also known as software environments or platforms, consist of a collection of programs to handle technical details.
Functions
Operating systems perform a variety of functions. These functions can be classified into three groups:
Resources – coordinate and monitor all computer resources.
User interface – provides interface between users, application programs, and computer hardware
Applications – load and run programs.
Categories
There are hundreds of operating systems but only three basic categories:
Embedded for handheld computers and smaller devices.
Network (NOS) control and coordinate computers on a network. Network server coordinates all network communication.
Stand – alone (desktop) for desktop and notebook computers; called client operating systems in networked environments.
Propriety operating systems are owned and licensed by a corporation; non-proprietary are free and called open source programs
Windows
Windows is the most widely used operating system. It is designed to run with Intel and Intel compatible microprocessors. There are numerous versions with Windows XP the latest version with the following features:

Mac OS
Apple’s Mac OS is an innovative, powerful, easy-to-use operating system designed to run with Macintosh computers. The latest version is the Mac OS X, which includes the following features:
UNIX was originally designed to run on mini-computers in network environments. Now, it is used by microcomputers and servers on the Web. There are many different versions of UNIX.
Linux, is receiving a great deal of attention today. It was originally developed by Linus Torvals in 1991. Linux is non-proprietary, free, and available from the Web. KDE and GNOME are Linux interfaces.
VSE/ESA and z/OS are mainframe operating systems from IBM. z/OS is the newest with a z/OSe version designed specifically to support e-commerce and Internet communications.
Palm OS is the most widely used operating system for PDAs. Two features are: Grafitti – a handwriting recognition system HotSync – communication support to share file and back up data with desktop and notebook computers.

Windows CE (Pocket PC) is a handheld operating system from Microsoft. Similar to Windows XP with support for special versions of Word, Excel, and Internet Explorer.
Anroid OS from Goggle
IOS – iPhone operating system
Blackberry OS
Utilities are specialized programs designed to make computing easier. The most essential utilities are:
Troubleshooting (diagnostic) programs to recognize the correct problems.
Antivirus programs to protect against computer viruses and other damaging programs.
Uninstall programs to safely remove unneeded programs and related files.
Backup programs to copy files in case originals are lost or damaged
File compression programs to reduce file sizes and storage requirements .
Utility suites combine several programs into one package. Typically, the suite costs less than buying each program individually.
Device drivers (drivers) are specialized programs to allow communication between hardware devices and the rest of the computer system.
While many device drivers are automatically installed, others must be installed by the user. Fortunate, Windows provides wizards such as the Add Printer Wizard to give step-by-step guidance.
Device drivers may need to be reinstalled or updated. Windows Update automates the process of updating device drivers.
Input is any data or instructions that are used by a computer. Input devices translate words, images, and actions that people understand into a form a computer can process.
KEYBOARDS
The most common way to input data. The most common types of keyboards:
Traditional are full-sized, rigid, and rectangular.
Flexible fold or roll up for easy packing and storage.
Ergonomic are designed to alleviate wrist strain associated with repetitive movement of typing.
Wireless free users from connecting wires.
PDA are miniature keyboards for PDAs.
Pointing is the most natural human gesture.
Pointing devices accept pointing gestures and convert them into machine-readable input. These devices include mice, joysticks, touch screens, light pens, and styluses.
MOUSE
The most common pointing device is the mouse which controls a mouse pointer. Some have a wheel button to scroll information.
Mechanical mouse –has a ball at the bottom and a cord connected to the system unit;
Optical mouse – no moving parts; uses light to detect mouse movements.
Cordless (wireless) mouse – battery-powered; typically uses radio or infrared light waves.
Scanners move across text and graphics. Scanning devices convert scanned text images into a form that can be processed by the system unit.

Optical scanners record light, dark, and coloured areas of scanned text or images. There are two types: flatbed and portable.

Bar code readers (scanners) used with electronic cash registers in supermarkets. Wand readers or platform scanners read UPC codes that are used to determine product descriptions and prices and to update inventory levels.
Character and mark recognition devices can recognize special characters and marks.
Magnetic-link character recognition (MICR) used by bank’s readers/sorters to help maintain customer account balances.
Optical-character recognition (OCR) used by retail stores to provide product price information readable by and wand readers
Optical-mark recognition (OMR, mark sensing) used to grade multiple choice exams by recognizing items selected.
Image capturing devices create or capture original images. These devices include digital cameras and digital video cameras.
Digital cameras record images digitally on a disk. Digital images are transferred or downloaded to system unit for further processing and/or printing.

Digital video cameras record motion on a disk or in the camera’s memory. WebCams (Web cameras) are specialised digital video cameras that capture and send images over the internet.
Digitizing devices convert a sketch or a figure into a form that can be processed by a computer. As writing device moves across a surface, the movements are recorded as a series of points.

Graphics tablets use a special surface and pen-like device to directly capture or trace images placed on the tablet.

Digital notebooks use a regular notebook placed over an electronic pad. The underlying pad records the movements of the pen as the user takes notes.
Audio input can take many forms including voice and music. Audio-input devices convert sounds into a form that can be processed by the system unit.
Voice recognition systems are a combination of a microphone, a sound card, and special software. Voice recognition is a common feature in much of today’s software. Word 2003 has a Language bar to switch between two modes: Voice command mode, Dictation mode
Musical Instrument Digital Interface (MIDI) is a standard that allows musical instruments to connect to MIDI ports in the system unit. MIDI devices send encoded digital signals representing musical sounds.
Assistive devices (accessibility hardware) allow those with visual or physical impairment to use computers and access technology. Alternative keyboards and mice, motion capture devices, and communication aids are assistive devices.
Alternative keyboards – allow those with limited mobility to enter data and text. Large print keyboards, Braille keyboards, and one-handed keyboards are common alternatives.
Alternative Mouse
Motion capture devices follow the movements of a disabled individual and translate those movements into commands
Communication aids use a combination of strategies to allow disabled individuals to interact with a computer
Output is a processed data or information. The most common types of output are text, graphics, audio, and video.
Text – words, sentences, and paragraphs; displayed on monitor, printed on paper, or read as audio output.
Graphics – images and pictures displayed or printed on paper.
Audio – sound converted from digital signals from the system unit to analog signals audible to humans.
Video – moving images displayed on a monitor; includes music video, TV, and movies.
Output devices are hardware to provide or create output. Devices include monitors, printers, audio-output, combination, and assistive output
Monitors (display screens, screens) present visual images of text and graphics. Monitor output is described as soft copy.
Features - Clarity is a function of several monitor features including resolution, dot pitch, refresh rate, and size.

Cathode-ray tubes (CRTs) use technology similar to a television. Low cost with excellent resolution. However, bulky and occupy considerable space on the desktop

Flat-Panel monitors (liquid crystal display, LCD) compared to CRTs are thinner, require less power, and used with all types of computers especially portable computers. TFT,

Gas plasma monitor (plasma display, gas discharge display) illuminates pixels with charged neon gas; thin, no distortion, more expensive than flat-panel.

Other monitors
Three specialised types of monitors are e-books readers, data projectors, and high-definition television (HDTV). HDTV is merger of microcomputers and television called PC/TV.
Printers translate information processed by system unit into output printed on paper. Output is described as hard copy.
Features - Some distinguishing features of printers include resolution, color capability, speed, and memory.

Ink-jet printers spray ink to produce high quality output. These printers are inexpensive and most widely used type of printer.

Laser printers use technology similar to photocopying machines.

Thermal printers use heat elements and heat-sensitive paper, used in scientific labs to record data. Color thermal printers are used to produce very high-quality artwork and text.
Dot-matrix printers form characters using small pins on a print head;
Plotters use output from digitizing tables and other devices to produce maps, architectural and engineering drawings.
Photo printers are special-purpose printers that produce photo-quality images from digital cameras.
Portable printers are small and lightweight; designed to work with notebook computers; may be ink-jet or laser, color, and typically connect to USB or parallel ports.
Audio-output devices translate audio information from the computer into sounds that people can understand.
Speakers and headphones are audio-output devices.

These devices are connected to sound cards within the system unit; the sound card captures as well as plays back recorded sounds.

Audio-output devices used to play music, vocalize language translations, and communicate information from the computer system.
Common combination devices include;
Fax machines (facsmile transmision machines) send and receive images via standard telephone lines. Fax/modem board operates as fax and modem.
Multifunctional devices (MFD) typically combine the capabilities of a scanner, printer, fax, and copy machine.
Internet telephones send and receive voice communication. Telephony (internet telephony, IP, Telephony, Voice-over IP, VoIP) uses internet to place very inexpensive long distance calls.
Assistive output devices make it possible for disabled individual to print, view, or hear computer output. Two categories are:
Braille Output Devices
There are several types of Braille devices to assist the blind or visually impaired.
Braille display – uses specialized software to read text from a monitor and then display the text on a type of monitor with moving Braille symbols.
Braille printers (Braille embossers) – work like dot-matrix printers to output Braille on printed pages.
Voice Output Devices
Reading devices convert printed text to speech.
Screen readers convert text displayed on monitor to speech.


SOURCE: (ISD) SAMUEL AFRIYIE SAKYI