Memory, CPU, Input Devices, Output Unit, Software

Memory: Stores data and instructions for processing. Types: RAM (temporary) and ROM (permanent).

CPU (Central Processing Unit): The “brain” of the computer; processes instructions and performs calculations.

Input Devices: Tools for entering data into a computer, e.g., keyboard, mouse, microphone.

Output Unit: Displays or outputs processed data, e.g., monitor, printer, speakers.

Software: Programs and operating systems that control hardware and perform tasks.

Memory

The Memory Unit is the part of the computer system that holds data and instructions for processing. Although it is closely associated with the CPU, in actual fact it is separate from it. Memory associated with the CPU is also called primary storage, primary memory, main storage, internal storage and main memory. When we load software from a floppy disk, hard disk or CD-ROM, it is stored in the Main Memory.
There are two types of computer memory inside the computer:
• Primary Memory
• Secondary Memory

Primary Memory

Primary storage, presently known as main memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner. However, the primary memory can hold information only while the computer system is ON. As soon as the computer system is switched off or rest, the information hold in primary memory disappears. Also it has limited storage capacity because it is very expensive. It is made up of semiconductor devices. RAM, ROM, CACHE, Register are the types of primary memory.

Random Access Memory (RAM)

RAM is the read write memory of the computer system. RAM is considered random access because any word can in the memory can be directly accessed in any order. It is volatile in nature. The storage capacity of RAM is measured in bytes. RAM plays an important role in the internal operation of the processor. RAM can be further divided into SRAM and DRAM.

DRAM: DRAM stands for Dynamic Random Access Memory. It is most common type of RAM used to store data and instructions in Micro Computer. The stored data will be lost even in on state after few millisecond. So, it needs to be refreshed (recharging the capacitors). It is further sub categorized into Synchronous Dynamic RAM (SDRAM) and Rambus Dynamic RAM (RDRAM).
SRAM: SRAM stands for Static Random Access Memory. It does not require continuous refreshing. It is faster and expensive. Special application such as cache and ROM use SRAM chips.

ROM (Read Only Memory)

The ROM contains instructions that are permanently stored on the chips by the manufacturers themselves. The instruction in the ROM can be read but cannot be modified. ROM can be categorized as masked programmed (ROM) and user programmed (PROM, EPROM, and EEPROM) on the basis of programming. The ROM contains Basic Input/ Output System (BIOS) and devices like printer uses the ROM for information storage. The Types of ROM are:

PROM: Programmable Read Only Memory is a Blank ROM chip in which user can write his own instruction and data only once. Once the programmer writes the micro-code on the prom chip, it functions like a normal ROM chip.

EPROM: Erasable Programmable Read Only memory are the ROM in which the data written can be erased by exposing it to ultra violet light. They are used to store program that needs updating. So data or program written in EPROM can be changed and new data can be added to this type of ROM.

EEPROM: Electrically Erasable Programmable Read Only Memory is special type of PROM that can be erased by exposing it to relatively high voltage of an electric charge on byte by byte basis without removing the chip. It can be rewritten electrically.

Cache Memory

Cache is a special, high speed and expensive semiconductor memory placed between RAM and CPU. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. Cache memory is placed in between CPU and RAM so that the operation of main memory and cache memory together can meet the speed requirements of the high speed CPU. There are two types of processes in cache: cache hit and cache miss.

Cache hit: At first processor, send desired data to cache, if data is available then the event is called cache hit.

Cache miss: When the processor sent address is not present in cache, event is called cache miss, after cache miss the data of main memory is copied for next cache hit.

There are two types of cache memory – internal cache and external cache.
Cache presents in the CPU is known as internal cache and cache presents in outside CPU is known as external cache. In general cache has two levels, level1 (L1) and level2 (L2). In which L1 is smaller and the faster among two and L2 is larger but slower.

Secondary Memory

Secondary storage, sometimes called auxiliary storage, is all data storage that is not currently in a computer’s primary storage or memory. This is computer memory that is not directly accessible to the processor but uses the I/O channels. It is for storing data not in active use and preserves data even without power, meaning it is non-volatile. In a personal computer, secondary storage typically consists of storage on the hard disk and on any removable media, if present, such as a CD or DVD.

The storage device can be categorized into two types, based on the type of data access. They are sequential and random access. In sequential access devices the data is written or read in sequence one after another. Magnetic disks, Optical disks are example of random storage. Random access is much faster than sequential access and uses more than one read write head.
Similarly based on the technology, the storage device can be divided into semiconductor memory, magnetic storage and optical storage.

Magnetic Memory:

Magnetic memory refers to system that keep information or data on a magnetized material. The surface of these devices are coated with magnetically sensitive material such as iron oxide which can be magnetized. The presence of magnetic field represents 1 bit and the absence represents the 0 bit. The disk is magnetically mapped before use creating sectors and tracks known as formatting or initializing.

Magnetic Disk

Magnetic disk is most widely used storage medium for computers. A magnetic disk is circular metal or plastic disk coated on both side with iron oxide. The data on magnetic disk is recorded as magnetic field. The instructions are accessed directly or randomly. There are two fundamental type of magnetic disk.

Hard Disk

Hard disk is the most commonly used storage device in personal computers and laptops. A hard disk contains one or more platter mounted on central spindle. Both side of platter is coated with magnetic material and used to store information. Each platter has two read/write heads, one for each side. ALL read write head are attached to a single access arm so that they can move independently. The standard size of hard disk is 3.5 inch in diameter. It rotates at the speed of 3600 rpm to 1500 rpm and the average access time is about 15ms.

Floppy Disk

The floppy disk is a thin and flexible plastic disk made of up Mylar coated on both side with magnetic recording material. They have low storage capacity and are very slow compared to other storage devices. The standard floppy disk size is 3.5 inch and has a rigid plastic cover. The rotation speed of the disk is 360 rpm and average access time is 150- 250 ms.

Magnetic Tape

Magnetic tape is Sequential access device used in super and mainframe computer. It is used mainly to provide backup or duplicate storage. The magnetic tape is a plastic ribbon with width 0.25 inch to 1inch and one side coated with magnetic recording material which can be magnetized. The data storage capacity can be 500MB, 2 GB, 4 GB or more.

Flash Memory

Flash memory is a type of non-volatile memory that can be erased electronically and reprogrammed similar to EEPROM. Flash memory works much faster than traditional EEPROMs because it writes data in chunks, usually 512 bytes in size, instead of 1 byte at a time. Flash memory are used in mobile computers and devices to store data and programs, for example, they are used in PDAs, digital cellular telephones, set top boxes , digital voice recorder etc. flash memory can be used to simulate main memory and replace hard disk drives for permanent storage.

Pen Drive

Pen drive is portable USB (Universal Serial Bus) flash memory device that can be used transfer audio, video, and data files from one computer to another computer. It is portable and also called thumb, jump drive, key drive, and tokens etc. storage capacity of pen drive range from MB to GB.

Memory Card

Memory card sometime called as flash card is a small storage medium used to store data such as text, audio, pictures and video for use on small, portable or remote computing devices. It is nonvolatile memory and are unlikely to suffer mechanical difficulties.

Optical Disk

An optical device is an electronic storage medium that can be written and read using a low powered laser beam. It has high storage capacity and is relatively cheaper. It is used as backup storage. The information on optical disk is stored in the form of land and pits.

CD-ROM (Compact Disk – Read Only Memory)

CD-ROM is an optical disk that uses laser technology to store and read data to and from disk. CD-ROM are popularly used to distribute computer software, including games and multimedia applications, though any data can be stored. It is non- volatile memory and readable by computer with a CD- ROM drive.

CD- R (Compact Disk – Recordable)

CD- R is a blank writable disc and drive that is capable of having information written to the disc once. Once data is written to CD- R it cannot be changed. The CD- R is coated with photo sensitive organic dye that allows a user to record information.

CD- RW(CD Rewritable)

CD- RW can be reused by erasing the content of the CD and again writing data on it. Like regular CDs, CD-Rs CD- RWs are composed of a polycarbonate plastic, a thin reflective metal coating and a protective outer coating. CD- R is write once read many recording format in which a layer of organic polymer dye between the polycarbonate and metal layer serves as the recording medium.

DVD (Digital Versatile/Video Disc) ROM

DVD is the high capacity optical disc with storage capacity from 4.7 GB to 17 GB. It can store any kind of data such as text, image, audio, video. The latest generation DVD ROM uses layers of data tracks and DVD- ROM drive OR DYD reads data from first layer then look up in second layer and so on.

DVD-R

DVD-R is a DVD recordable format with typical storage capacity of 4.7 GB. Like, CD-R a DVD-R system lets user to record data onto a special recordable digital video disk, using a special drive.

DVD-RW

A DVD- RW is a rewritable optical disk with equal capacity to a DVD-R, typically 4.7 GB. The primary advantage of DVD- RW over DVD-R is the ability to erase and rewrite to DVD-RW disc. DVD-RW is used for non- volatile data such as backups and collection of files.

Blue Ray Disk(BD)

The new generation optical disk developed to enable recording, rewriting and play back of high definition video (HD), as well as storing large amount of data. It can hold up to 25 GB on a single layer disc and 50 GB on dual layer disc. Unlike other optical disc, instead of using red laser to read and write data, BD uses blue- violet laser beam. Hence, called Blue Ray Disc.

Central Processing Unit (CPU)

CPU is responsible for activating and controlling the operations of other units of a computer system. It is also referred to as the brain of computer. The functions of CPU are:
To carry out processing.
• To give command to all parts of computer system.
• To control the sequence of operation.
• To control the storage of data or instructions.
• To perform arithmetic calculation such as addition, subtraction.

CPU consists of three main parts:

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)
3. Register Array

Control Unit (CU)

Control Unit is responsible for coordinating various operations of a computer. It uses time signals to do that. The control unit determines the sequence in which computer programs and instructions are executed. It also acts as a switch board operator when several users access the computer simultaneously. In simple words, it acts like the supervisor seeing that things are done in proper fashion. The functions of Control Unit are:

1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.

Arithmetic and Logical Unit (ALU)

The actual processing of the data and instruction are performed by Arithmetic Logical Unit. ALU takes care of various calculations. The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required. After processing the output is returned back to storage unit for further processing or getting stored. ALU can perform following function:
1) Integer arithmetic operations (addition, subtraction, and sometimes multiplication and division).
2).Bitwise logic operations (AND, NOT, OR, XOR)
3).Bit-shifting operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension). Shifts can be interpreted as multiplications by 2 and divisions by 2.

Register Array

Register is a special temporary storage location within the CPU. Register quickly accept, store and transfer data, instructions and data that are being used immediately. Registers
• Can be thought of as fastest memory locations.
• Storage capacity is small.
• Are relatively 32 bit and 64 bit registers.
• Are used for temporary storage of immediate results.

Although register varies from computer to computer, there are some registers common to all computers. Some of them are:
Memory Address Register (MAR): It holds the active memory location.
Memory Buffer Register (MBR): It holds the content of accessed memory word.
Program Counter (PCR): It holds the address of next instruction to be executed.
Accumulator Register (AR): It holds the data to be operated upon, the immediate result, and the result of processing.
Instruction Register (IR): It holds the current instruction being executed.
Input/ Output Register (IO Register): It is used to communicate with input and output devices.

Input Device

Input devices are the devices used for entering or inputting data and instructions to the computer system. It is a medium of communication between user and the computer. In old computers, the punched card readers, paper tape reader were used as input devices. Now a days the most common type of input device are keyboard and mouse.

Keyboard

Keyboard is one of the primary and most common device used for entering data. It is similar to electric typewriter and contains key for each alphabetic characters, digits and special characters. The most common type of keyboard are QWERTY keyboard. Some standard keyboard are:
XT (Extended Technology) 83 keys
AT (Advanced Technology) 101 keys
Enhanced Technology: 103 keys or more (multimedia)

Mouse

Mouse is a small handheld pointing and clicking device used to control the position of the cursor on screen. The mouse has two or three button on the top of its body. A mousse allows user to create graphics such as lines, curves and freehand shape on the screen. The types of mouse are:

Mechanical mouse: It has a rubber or metal ball at its bottom, and an electronic circuit containing circuit sensors. Whenever the mouse is rolled over a flat surface, the pointer moves in the same direction as of mouse.

Optical mouse: It has advance feature and uses laser technology to detect the mouse movement by optical sensors.

Optomechanical mouse: It is similar to mechanical mouse but uses optical sensor to detect the motion of the ball

Trackball

Trackball is a pointing device similar to mouse, but is stationary pointing device with a ball on its top. The ball is rolled or rotated with fingers to move the cursor or pointer around the screen. Track ball is suited to portable computers such as on laptops.

Touchpad

A touchpad is small, flat rectangular stationary pointing device with sensitive surface of 1.5 to 2 inches square. Finger is slide over the surface to move the pointer and tapped for clicking. The touchpad pointing devices are usually used in laptop computers.

Joystick

Joystick is a pointing input device with a moving handheld lever and buttons. The lever is used to control the movement of pointer on screen and the button of the joystick is pressed to activate certain events. It is used principally used in video games and some computer aided system.

Light Pen

Light pen is a light- sensitive stylus, or pen like device that detect the presence of light. Photocell is mounted at its front end and when touched with the monitor screen, the photocell detects or senses a position of display screen. It is useful for graphics work like CAD package and is mainly used by engineers, graphic designers and illustrators.

Touch Screen

A touch screen is a video display screen that has sensitized to receive input from the touch of a finger or some pointed object. It is a screen with touch sensitive points or program icons. It is modern and advanced technology applied in laptops, camera, mobile and lot more modern electronic devices.

Digitizing Tablet

A digitizing tablet most commonly known as Graphic tablet connected by a wire to stylus or puck. It is mainly used for making maps and drawings.

Digital Camera

Digital Camera is a camera that takes video or still photographs or both, digitally by recording images via an electronic image sensor. A digital camera uses photosensitive device such as charged coupled device (CCD) to digitize the images. It can take photo and load them directly from the camera digitally to a main storage or secondary storage device.

Scanner

Scanner is a device that optically scans images, printed text, handwriting, or an object and converts it to a digital image. The scanner uses laser technology to scan the image of the printed paper and store it into the computer. The most common type of scanner are handheld scanner and flatbed scanner.

Bar code Reader

Data coded in the form of light and dark lines or bars are known as bar codes. Bar code reader is a photo- electric scanner that reads bar code. It consists a light source, a lens and a light sensor translating optical impulses into electrical ones. It is mostly used in supermarket, library, bookshops, cinema hall etc.

Optical Character Reader

OCR reads printed character directly, converts them into appropriate codes and store them in a computer. It is widely used to convert books and documents into electronic files.

Optical Mark Reader

OMR is a device that reads pencil marks or shades and converts them into computer usable form. It is mainly used to read the answer sheets of multiple choice questions and survey form, Graduate Record Examination etc.

Magnetic Ink Character Reader

MICR is an input device, which reads the characters printed using magnetic ink. MICR is mostly used in bank for cheque processing.

Smart Card

A small electronic device, similar to credit card which contains electronic memory and possibly an embedded Integrated Circuit (IC). Smart card are used for variety of purposes including storing patient’s medical records, storing digital cash, Public telephone etc.

Microphone

It is an input device for recording voice or sound. It is mainly used for voice mail, video chat, conferencing etc. Besides in computer system, it is also used in many other system such as telephones, tape recording, motion picture production, radio and television broadcasting etc.

Output Unit

Devices that are used to get output from a computer in readable form is called output devices. Some of commonly used output devices are video display unit (VDU) and printers, speaker. Output is normally classified as

Softcopy Output

Softcopy refers to data that is shown on display screen or sound produced by speaker. It is temporary and is has no physical presence. Eg: Monitor, Speaker

Monitor

Monitor is most commonly used output device that consist of a screen and the electronic components that produce the output on the screen temporarily. The output received on the screen is called softcopy output. Monitor can be divided into following categories:

On the basis of Color Display

Monochrome Monitor: In monochrome monitor information is displayed in two colors, one color (such as white, green, black, amber or grey) for fore ground and one color for background which is usually black. These monitors are used to display text only.
Grayscale Monitor: Grayscale monitor is a type of monochrome monitor that often uses grayscale to enhance the quality of graphics. They are used in handheld computers.
Color Monitor: These monitors can display 16 colors to several million colors. These monitors are sometimes called RGB. Today most of the computer uses color monitors.

On the basis of display technique

Cathode Ray Tube (CRT) monitor: A CRT monitor is similar to standard television set and contains Cathode ray tube. The CRT monitor creates a picture out of many rows or lines of tiny colored dots. The more lines of dot per inch, higher and clearer the resolution. CRT monitor consists of an electronic gun that shoots a beam of electrons through magnetic coil and moves back and forth across the back of screen.

Liquid Crystal Display (LCD) monitor: LCD is a flat panel monitor that uses the light modulating properties of liquid crystal. LCD has fluorescent tubes that emits light waves towards the liquid crystal cells, which are sandwiched between two sheet materials. When an electric charge passes through the cells, the cells twist and the twisting causes some light waves to pass and some to be blocked creating image on the screen. They are used in wide range of application including computer monitors, television, instrument panels, laptops etc.

Light Emitting Diode (LED) monitor: A light emitting diode is a semiconductor device that emits visible light when an electric current passed through it. The chip has two region separated by junction. The P region is dominated by positive charge and the n region is dominated by negative charge and the junction acts as barrier to flow of electrons. It is mostly popular for television set, desktop PC, laptop, mobile phones, tablet PC.

Gas Plasma Display: Gas plasma display uses a gas that emits light in the presence of an electric current. The technology uses predominantly neon gas and electrodes above and below the gas. When the electric current is passed between the electrodes, the gas glows. Plasma display are thinner than CRT display and brighter than LCD. Plasma display can be used to display either analog video signals or display digital computer input.

Hard copy output

Printer

Printer is a peripheral device used to print text, picture, illustration, figure and image. It is used to print hardcopy output. The quality of printer depends on following factors such as color, resolution, speed, memory ETC. Printers are divided into impact and non-impact printer.

Impact Printer

An impact printer has mechanism resembling those of the typewriter. i.e. produces output by striking a ribbon with a hammer. It can print more than a copy by using the carbon paper. Impact printer are noisy because of hammering action and slow technology for printing compared to non-impact printer. Dot- Matrix printer, Daisy wheel printer and line printer are some example of impact printer.

Non- impact Printer

They are most widely used printer and are faster and queiter than impact printers. It forms characters and images without making physical contact between printing mechanism and paper. It can print in different fonts, style and size. It cannot be used to print the multiple copies at a time. Laser printer, inkjet printer and thermal printer are some example of non-impact printer.

Dot- Matrix Printer: Dot- Matrix Printer is a common type of microcomputer impact Printer which contains a print head of small pins that strikes an inked ribbon forming characters or images. It is called dot matrix printer because it prints the character with combination of dots. It can print in both direction and multiple copies can be printed using Carbon paper. The output quality of dot matrix printer is poor, makes more noise and takes long time to print.

Daisy Wheel Printer: It is older type of impact printer which has removable print wheel- the flower like daisy wheel consisting of spokes. The character pattern are arranged all around the edge of wheel. When a letter is to be printed the wheel rotates so that the correct letter is against the ribbon and then the hammer hits the letter against the ribbon.

Line Printer: Line printer prints whole line at a time unlike dot matrix and daisy wheel that prints only one character at a time. The line printer may be chain or drum type. It can print text of fixed size and font. It is appropriate for continuous printing such as printing mark-sheet, bank statement, bill and receipt.

Inkjet Printers: Inkjet printer are non- impact printer which prints text and images by spraying tiny droplet of liquid ink onto paper. It is quieter and is widely used for personal purpose. Most color printing is done on ink jet printer because the nozzle can hold four different colors, CMYK. Ink jet printers can produce 360 or 720 dots per inch. Currently, most inkjet uses thermal inkjet or piezoelectric inkjet technology.

Laser Printer: Laser printer are Non- Impact printer used to print text and images in high quality, speed and resolution, ranging from 600 to 1200 dpi. They are called page printer because they print entire page at a time. Laser printer uses toner (black or colored powder) instead of liquid inks. Laser printers produce sharp, crisp images of both text and graphics.

Thermal Printer: Thermal printer uses colored waxes and heat to produce images by burning dots onto special heat sensitive paper. It can provide highest-quality desktop color printing available. They are expensive and require expensive paper.

Plotter

A plotter is an output device used to produce single or multiple colored images and drawings. It is especially used for creating maps and architectural drawings and sometimes complicated charts and graphs. It uses pen or inkjet mechanism to draw graphics and images. It produce uniform, precise and high quality images. The different types of plotter are Drum plotter, Micro- grip plotter, Flat- bed plotter and ink- jet plotter.

Speaker

Speaker are electro- acoustic transducer that converts electrical signals into sounds loud enough to be heard at distance. Speaker are soft copy output device that can be used to produce sound as output. Speaker produces and amplifies sound output.

Software

A set of instruction written for computer to perform a particular task is called software.
The term software refers to set of programs, procedures, and associated document describing the program and how they are to be used. Software is the interface between computer and the user and without software the computer is useless. The software is categorized into two types:

• System software
• Application software

System Software

System software is computer software designed to operate the computer hardware and to provide a platform for running application software. It is responsible for resource management, memory management, file management, task scheduling, software repairing, language translation and system maintenance. It is collection of operating systems, device drivers, servers, windowing system and utilities. The most commonly known system software are: Operating System, Language Processor and Utility Programs.

Operating System

OS is most important program that runs on a computer. OS is the link between hardware, application software and user. Operating system control and coordinates the overall operations and resources of the computer system. Without operating system one cannot communicate with the computer. Some examples of operating system are Windows XP, Linux and UNIX.

Language Processors

Language processor translates statement written in one language to statement in another language. Language processor converts source code into object code and every programming language has its own language processor. There are three types of language processors: Assembler, Compiler and interpreter.

Assembler: Assembler is a translator that converts code of assembly language into the machine language. As computer only understands machine language, assembler is needed to translate source code into object code. The assembly language is used to translate the source code into object code once, then executed to get the result.

Interpreter: An interpreter is a translator which translates high level language into a machine language, one line at a time and executes line of the program after it has been translated. It translates one statement of a program, executes the statement immediately and moves to the next statement. When error is encountered the process of translation is halted and error message is displayed. Programming language such as BASIC, LISP use interpreter.

Compiler: A compiler is a translator that translates high level programming language into machine instruction at a once and then it can be immediately executed anytime thereafter. The process of translating from source code to object code is called compilation. The source code is translated to object code successfully only if it is error free. The object code can be used number of times without executing it again. Programming language like C, C++, JAVA, and COBOL uses compiler.

Utility Software

Utility software is computer software designed to help manage and tune the computer hardware, operating system or application software. The utility programs are part of operating system which enhances the performance of the OS and the system to its optimum. Some of the utility software are Disk defragmenters, Disk checkers, Disk Practitioners, Disk Cleaners, Antivirus, and Network Manager.

Application Software

Application software is a set of one or more programs designed to solve a specific problem, or do a specific task. This program directs a computer to solve user- oriented problems such as preparing bills, calculation, preparing mark-sheet etc. Software developed for user purpose is called application software and is generally developed using high level programming language. Example of application software are MS- Word, MS- Excel, Accounting software, banking software.
Application software can be:

• Package software
• Tailored software

Packaged Software

Packaged software is a generalized set of program designed and developed for general purpose. It is generally large sized, bug free, advance and standard software for special work. Database, graphics, animation, web designing software are packaged software.

Tailored software

Tailored software is a small software, developed in high level language for specific small task. This type of software is developed for some specific purpose, for solving specific problem of specific users and organizations. Eg: Hotel Reservation System, E- Payment system etc. It is developed by using high level language like C, C++, and JAVA etc.

Frequently Asked Questions (FAQ)

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