Computers are showing up everywhere you look, and even in places you can't see. Computers check out your groceries, pump your gas, dispense money at the ATM, turn the heat on and off, control the way your car runs. They're everywhere!

A computer is an electronic device that executes the instructions in a program.Modern computers are electronic and digital. A computer has four functions:

a. Accepts data Inputb. Processes dataProcessingc. Produces output Output d. stores resultsStorage

All computer systems perform the following five basic operations:- Inputting:The process of entering data and instructions into the computer system. Storing:Saving data and instructions to make them readily available for additional processing, as when required. Processing:Performing arithmetic operations (add, subtract, multiply, divide, etc), or logical operations on data, to convert them into useful information. Outputting:The process of producing useful information or results for the user, such as a printed report or visual display Controlling:Directing the manner and sequence in which all of the above operations are performed.

Input Unit : - It accepts or reads the instructions and data from the outside world- It converts these instructions and data in computer acceptable form.- It supplies the converted instructions and data to the computer system for further processing.Output Unit :- It accepts the results produced by the computer, which are in coded form, and hence, cannot be easily understood by us.- It converts these coded results to human acceptable (readable) form.- It supplies the converted results to the outside world.Memory Unit: - Memory unit are to store the data and instructions required for processing - They are to hold the final results of processing, before these results are released to an output device The Memory unit is comprised of the following 2 types of storage:Primary storageSecondary storage

Arithmetic Logic Unit: The arithmetic logic unit (ALU) of a computer system is the place, where the actual execution of the instructions takes place, during the processing operation. ALUs are designed to perform the arithmetic operations (add, subtract, multiply & divide) and logical operations or comparisons.Control Unit The control unit acts as a central nervous system, for other components of the computer system. It manages and coordinated the entire computer system

Central processing unit (CPU): The control unit and ALU of a computer are jointly known as the Central Processing Unit The CPU is the brain of a computer system & all calculations and comparisons are made inside the CPU. CPU is responsible for activating and controlling the operations of other units of the computer system.

A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip.

Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. A microprocessor can move data from one memory location to another. A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

The number of bits that the CPU can process simultaneously. Normally groups of 8, 16, 32, 64, 128 bit words are processed as a unit during input, output and logic instructions.

Word size is a major factor in determining the speed of a processor.

Buses are the lines along which data is transmitted. This data can be in the form of data and instructions as well the addresses of the data and the instructions.

The width of a data bus determines how many bits can be transmitted simultaneously and the maximum address which can be referenced.

An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory

A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory

Instructions and data are held in main memory, which is divided into millions of individually-addressable storage units called bytes. One byte can hold one character, or it can be used to hold a code representing, for example, a tiny part of a picture, a sound, or part of a computer program instruction. The total number of bytes in main memory is referred to as the computers memory size. Computer memory sizes are measured as follows:1 Kilobyte (Kb)=1000 bytes (to be exact, 1024 bytes)1 Megabyte (Mb)=1,000,000 (1 million) bytes1 Gigabyte (Gb)=1,000,000,000 (1 billion) bytes1 Terabyte (Tb)=1,000,000,000,000 (1 trillion) bytes

Hardware:the physical parts of the computer.Software:the programs (instructions) that tell the computer what to doData:individual facts like first name, price, quantity orderedInformation:data which has been massaged into a useful form, like a complete mailing addressDefault:the original settings; what will happen if you don't change anything.

Input The input hardware allows you to enter data into the computer. The primary devices used are the keyboard and mouse. Keyboard The keyboard looks like the typewriter. A numeric keypad is located to the right of the keyboard. Mouse The mouse is a device that allows you to control the movement of the insertion point on the screen. There are other input devices, such as touch screen, joystick, modem, scanner, and voice recognition systems.

Touch Screen:A display screen that is sensitive to the touch of a finger or stylus. Touch screens are very resistant to harsh environments where keyboards might eventually fail.

Joy Stick:A pointing device used to move an object on screen in any direction. Joy sticks are used extensively in video games and in some CAD systems

Light Pen:A light-sensitive stylus wired to a video terminal used to draw pictures or select menu options. The user brings the pen to the desired point on screen and presses the pen button to make contact

Processing The central processing unit or (CPU) is the "brain" of your computer. It contains the electronic circuits that cause the computer to follow instructions from ROM (read only memory) or from a program in RAM (random access memory).

CPU contains three parts.

Arithmetic Logic Unit ALU is where the "intelligence" of the computer is located. It can add and compare numbers.

Memory Memory contained on a chip arePrimary Memory

Primary Memory:It is also known as main memory, is used to hold pieces of program instructions and data.It is of 2 types:-

RAM (Random Access Memory) ROM (Read Only Memory).

ROM memory has been installed on your computer by the manufacturer and can not be altered.ROM determines all the basic functions of the operation of your machine, such as startup, shut down, and placing a character on the screen.RAM is temporary memory, which displays the information you are working on. RAM remembers what you see on your screen while you are working. Today's applications required large amounts of temporary memory, which may require you to upgrade and add more RAM memory.

3. Control Unit

This is the part of the unit, which directs information to the proper places in your computer, such as calculation of information by the ALU unit or to store and print material.

Short for programmable read-only memory, a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROMs retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process.

To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

An EPROM (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased.

What is an EEPROM?

Pronounced double-ee-prom or e-e-prom, short for electrically erasable programmable read-only memory. EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster.

Very fast memory used to improve the speed of a computer, doubling it in some cases Acts as an intermediate store between the CPU and main memoryStores the most frequently or recently used instructions and data for rapid retrieval Generally between 1Kb and 512KbMuch more expensive than normal RAM

Memory Cache speeds up a computer by storing data the computer has recently used. There are 2 types : Internal & External

External CacheIf the computer cannot find what it needs in the Internal Cache, it looks in the external cache. This is usually located on the Motherboard. In some CPU chips the External cache is built in.Internal CacheWhen the computer needs data it first looks in the Internal cache. This is located on the CPU chip and provides the fastest way for the computer to get data.

Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed. Virtual memory

MotherboardThis is the main circuit board that all of the other internal components connect to. The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. For example, a sound card can be built into the motherboard or connected through PCI (Peripheral Component Interface).

Output Output devices such as a monitor or printer make information you input available for you to view or use. Monitors:A monitor's front is called a screen with a cathode ray tube (CRT) attached to the screen. Portable computers use a (LCD) liquid crystal display. Today's super video graphics array (SVGA) monitors display 256 sharp and clear colors.

Printers A device that prints text or illustrations on paper. There are two different types of printers. 1) Impact printer2) Non Impact printer

Impact printers

Include all printers that work by striking an ink ribbon. Dot-matrix are impact printers.Dot-matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.

Daisy-wheel:

Characters are fully formed on the "petals", like typewriter keys. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy-wheel printers produce letter-quality print but cannot print graphics. It is very expensive and very loud

Line printer:

Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print. Daisy-wheel and Line printers can print only text.

Non-impact printers Include laser printers and ink-jet printers. The important difference between impact and non-impact printers is that impact printers are much noisier.

Ink-jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics.

Laser:Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.

Thermal printer:

Uses heat on chemically treated paper to form characters An inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in calculators and fax machines.

A device that draws pictures on paper based on commands from a computer.Plotters differ from printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only simulate lines by printing a closely spaced series of dots.Plotters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory.

Audio Output DevicesWindows machines need special audio card for audio output.Macintosh has audio playback built in.Audio output is useful for:MusicCD player is a computer.Most personal computers have CD players that can access both music CDs and CD-ROMs.Multimedia

Integrated Drive Electronics (IDE) Controller This is the primary interface for the hard drive, CD-ROM and floppy disk drive. Peripheral Component Interconnect (PCI) Bus The most common way to connect additional components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug into. SCSI Pronounced "scuzzy," the small computer system interface is a method of adding additional devices, such as hard drives or scanners, to the computer.

Graphics card This translates image data from the computer into a format that can be displayed by the monitor. Sound card This is used by the computer to record and play audio by converting analog sound into digital information and back again. AGP Accelerated Graphics Port is a very high-speed connection used by the graphics card to interface with the computer.

Parallel PortSerial PortsUSB Ports

SERIAL PORTConsidered to be one of the most basic external connections to a computer, the serial port has been an integral part of most computers for more than 20 years. Although many of the newer systems have done away with the serial port completely in favor of USB connections, most modems still use the serial port, as do some printers, PDAs and digital cameras. Few computers have more than two serial ports.

If you have a printer connected to your computer, there is a good chance that it uses the parallel port. While USB is becoming increasingly popular, the parallel port is still a commonly used interface for printers. Parallel ports can be used to connect a host of popular computer peripherals: Printers Scanners CD burners External hard drives Iomega Zip removable drives Network adapters Tape backup drives Parallel Ports

The goal of USB is to end all of these headaches. The Universal Serial Bus gives you a single, standardized, easy-to-use way to connect up to 127 devices to a computer. Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes: Printers Scanners Mice Joysticks Flight yokes Digital cameras Webcams Scientific data acquisition devices Modems Speakers Telephones Video phones Storage devices such as Zip drives Network connections Connecting a USB device to a computer is simple -- you find the USB connector on the back of your machine and plug the USB connector into it.Universal Serial Bus (USB) Ports

The rectangular socket is a typical USB socket on the back of a PC. A typical USB connector, called an "A" connection A typical "B" connection

Power supply An electrical transformer regulates the electricity used by the computer. Hard disk This is large-capacity permanent storage used to hold information such as programs and documents. Operating system This is the basic software that allows the user to interface with the computer.

Secondary Memory Secondary storage is also know as auxiliary memory, this memory is non-volatile. Secondary memory can store large volume of data on a permanent basis

The four most important characteristics of storage devices:Speed and access timeCapacityType of access

Speed (Access time) - How fast information can be taken from or stored onto the computer memory devices medium.Electronic circuits: Fastest to access.40 billionths of a second.Floppy disks: Very slow in comparison.Takes up to 1/2 second to reach full speed before access is even possible.

UnitDescriptionApproximate Size1 bit1 binary digit1 nibble4 bits1 byte8 bits1 character1 kilobyte1,024 bytes1/2 page, double spaced1 megabyte1,048,576 bytes 500,000 pages1 million bytes1 gigabyte1,073,741,824 bytes 5 million pages1 billion bytes1 terabyte1 trillion bytes 5 billion pagesCapacity The amount of information that can be stored on the medium.

There are two methods of accessing information- Sequential accessDirect accessSequential Access:Information on a sequential access device can only be retrieved in the same sequence in which it is stored. For example: preparation of monthly pay slips, monthly electricity bills etc.Magnetic tape is an example of a sequential-access storage device.The magnetic tape is a plastic ribbon, -1/4 inch wide and 50-2400 feet long. The tape ribbon is itself stored in small cartridge or cassette.

Direct Access:Information on a direct access device can be retrieved randomly.Magnetic disk is the storage medium for direct accessMagnetic disk is broadly classified into 2 types:Floppy DiskHard Disk

Floppy Disk:A floppy disk is a circular piece of oxide-coated plastic that stores data as magnetic spots. Personal computers most commonly use floppy disks that are 3 inches in diameter. A Floppy disk drive is used to read/write data from /to floppy disks.

Hard Disk

Hard Disk is the secondary storage device, which are made of rigid metal.

Optical Disks: CD-ROM and DVDCD-ROM (Compact Disk - Read Only Memory)By its definition, CD-ROM is Read Only.Special CD drives burn information into blank CDs.Burn: A laser is used to burn craters into the surface to represent a binary 1.Two main types of CDs:CD-R (Compact Disk - Recordable)CD-WR (Compact Disk - ReWritable)It takes longer to write to a CD-R than a hard drive.Special software is needed to record.

DVD (Digital Versatile Disk)

Allows up to 17 gigabytes of storage (from 4.7 GB to 17 GB).Compatible with older CD-ROM technology.

Hand-held ComputerA hand-held computer or personal organizer is a small portable computer with various functions, for example diary, phone book, note book, etc.

Personal ComputerPC or desktop computers are used both in isolation, for example in home computing, and as networked computers (a network is two computers or more that are linked together either by cabling or infra-red).

Palmtop

More commonly known as Personal Digital Assistants (PDAs), palmtops are tightly integrated computers that often use flash memory instead of a hard drive for storage. These computers usually do not have keyboards but rely on touchscreen technology for user input

Workstation

A desktop computer that has a more powerful processor, additional memory and enhanced capabilities for performing a special group of task, such as 3D Graphics or game development.

Laptop computer

Laptop computers have similar computing power to personal computers, but are much lighter and portable. Laptops have a removable, chargeable battery pack so that the user does not always require a mains electricity supply for its` use.

Server

A server is a large powerful computer, usually with a large amount of storage (hard drive) space. Networked computers are attached to one or more central network servers, allowing users to share files, use network software (e.g. a large email client), or connect to the internet.A Server may act as one or more of:- compute server: to run programs- file server: to store files centrally- mail server: to route mail messages- web server: to store web files etc.

Main Frame

The main frame is the workhorse of the business world. A main frame is the heart of a network of computers or terminals which allows hundreds of people to work at the same time on the same data.

Supercomputer

The supercomputer usually costs hundreds of thousands or even millions of dollars These are used for jobs that take massive amounts of calculating, like weather forecasting, engineering design and testing, serious decryption, economic forecasting, etc.

Minicomputer

Minicomputers fall in between microcomputers (PCs) and mainframes (enterprise servers). In fact, the ordinary new PC is much more powerful than minicomputers used to be. Originally this size was developed to handle specific tasks, like engineering and CAD calculations.

Hardware and Software

Hardware is any physical part of the computer setup. This means the monitor, keyboard, mouse, CD-ROM drive, printer, etc. Software consists of the programmes that allow you to work on a computer. Operating systems, word processors, spreadsheets, games and database management systems are all examples of software.

Hand-held (HPC) PDA Tablet PC Laptop/Notebook Desktop Tower Workstation

Why is it so important?The economies of ALL developed nations are dependent on software.More and more of our daily lives are being supported/monitored by softwareThe engines of our carsOur washing machinesGetting on a bus/train

Software is the part of a computer that makes it useful.Software is a set of instructions (Programs).These are acted upon (executed) by the hardware.Software is also the documents that describe the operation and use of the programs.

Generally software takes in data and processes it into information.

System SoftwareThis type of software exists at the Operating System layer. It is the operating system itself, compilers, editors.any kind of software that supports the execution and/or development of applications.Application SoftwareReal-time SoftwarePrograms that monitor/analyse/control real world events. A nuclear power plant cooling system is a good example.

Application SoftwareBusiness SoftwareBusiness Information Systems such as payroll, accounts and order management/tracking. There are off-the-shelf packages available for small businesses, however large businesses usually develop their own software.Engineering and Scientific SoftwareTypically number crunching programs for areas such as astronomy, molecular biology, weather forecasting and Computer Aided Design (CAD) for engineers. Generic programs do exist for some of these areas, however research usually requires new software to be developed.

Application SoftwareEmbedded SoftwareIntelligent products such as cookers, washing machines and microwaves use embedded software that typically resides in a Read Only Memory (ROM). Due to the individual nature of such products this software is usually developed/tailored for each.Personal Computer SoftwareSpreadsheets, word processors, computer graphics, multimedia and database applications are typical. This type of software is predominantly off the shelf but does go through many versions to remove bugs and increase functionality.

Application SoftwareArtificial Intelligence (AI) SoftwareAI is used to solve complex problems such as scheduling the maintenance of manufacturing equipment to minimise their shutdown. Other uses include pattern recognition (speech/visual). This software is typically newly developed for each application.

The application of computers through software development is only limited by our imaginations(and its cost)

As hardware will always eventually wear out, it will need to replaced.

Software on the other hand, doesnt wear out in this traditional sense, but will become increasingly less useful as users requirements for it changes over time.This means that software needs to be either periodically updated or replaced.

Understanding the process of software development is therefore paramount in keeping software systems/applications continually useful to its users.

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