Computer System Organization

Computer contains input devices (keyboard, mouse, A/D (analog-to-digital) converter, etc.), a computational unit, and output devices (monitors, printers, D/A converters). The computational unit is the computer's heart, and usually consists of a central processing unit (CPU), a memory, and an input/output (I/O) interface.

Characteristics of Computer• Speed - The speed of a computer is incredibly faster

than what man can possibly record or calculate normally.

• Storage - A computer system can store a large amount of data in a systematic manner.

• Accuracy and Reliability - Inspite of high speed, the computers are quite accurate and reliable in their calculations. the accuracy of operation of a computer is always 100%.

• Automatic - Once the process has been initiated, computer is quite capable of functioning automatically. it does not require a prompt from an operator at each stage of the process.

• Diligence/Endurance - Is capable of operating at exactly the same level of speed and accuracy even if it has to carry out the most voluminous and complex operations for a long period of time.

• Scientific Approach - The entire approach to solving problems is highly scientific, objective and sequentially carried out, leaving no room for emotional & subjective evaluations made by man.

• Versatility - The wide use of computers in so many areas in day-to-day life is an ample evidence of its versatility.

Uses of Computer• Word Processing - Word Processing software

automatically corrects spelling and grammar mistakes.

• Medicine - You can diagnose diseases. You can learn the cures.

• Mathematical Calculations - Computing speeds of over a million calculations per second

• Banks - All financial transactions are done by computer software. They provide security, speed and convenience.

• Travel - One can book air tickets or railway tickets and make hotel reservations online.

• Examinations - Online exams and get instant results.

Generation of Computer• First Generation (1940-1956) - The first computers

used vacuum tubes for circuitry and magnetic drums for memory.

• Second Generation (1956-1963) - Transistors replaced vacuum tubes and ushered in the second generation of computers.

• Third Generation (1964-1971) - The development of the integrated circuit was the hallmark of the third generation of computers.

• Fourth Generation (1971-Present) - The microprocessor brought the fourth generation of computers, as thousands of integrated circuits we rebuilt onto a single silicon chip.

Types of Computer• Analog - Computer that uses the continuously-

changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved.

• Micro-computer - Computer with a microprocessor as its central processing unit.

• Mini-computer - A class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems.

• Mainframe - Are computers used mainly by large organizations for critical applications, typically bulk data processing.

• Super computer - A mainframe computer that is among the largest, fastest, or most powerful of those available at a given time.

• Hybrid - Computers that exhibit features of analog computers and digital computers.

Input Device - A hardware device that sends information into the CPU.

• Keyboard - An input device which uses an arrangement of buttons or keys.

• Mouse - A pointing device.• Trackball - A pointing device consisting of a ball.• Joystick - An input device consisting of a stick.• Digitizing Tablet - A computer input device that allows

one to hand-draw images and graphics.• Scanners - Device that optically scans images, printed

text, handwriting, or an object, and converts it to a digital image.

• Digital Camera - A camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor.

• MICR - Type of font capable of recognition using magnetically charged ink.

• OCR - The mechanical or electronic translation of images of handwritten, typewritten or printed text into machine-editable text.

• OMR - The process of capturing human-marked data from document forms.

• Bar-Code Reader - An electronic device for reading printed barcodes.

• Voice Recognition - Converts spoken words to text.• Light Pen - A small, photosensitive device connected

to a computer and moved by hand over an output .• Touch Screen - A monitor screen that can detect and

respond to something, such as a finger or stylus, pressing on it.

Output Deice - Any peripheral that receives and displays output from a computer.

Monitor - A device that displays images or symbols generated by computers

Characteristics of Monitors:• Resolution - T he number of distinct pixels in each

dimension that can be displayed.• Dot Pitch - Is a specification for a computer display

that describes the distance between dots (sub-pixels) of the same color on the screen.

• Refresh Rate - Is the number of times in a second that display hardware draws the data.

• Size - Is measured diagonally from one corner of the screen to another.

Types of Monitors• CRT - Is a vacuum tube containing an electron gun

and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen.

• Flat Panel - encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays.

• LCD Monitor/screen - Is a thin, flat panel used for electronically displaying information such as text, images, and moving pictures.

Printers A printer is a peripheral which produces a hard copy

of documents stored in electronic form. Types: • Daisy Wheel - A device used in some electric

typewriters and printers, consisting of printing characters fixed at the ends of spokes on a wheel.

• Dot Matrix - Is a type of printer with a head that runs back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper.

• Inkjet - Is a type of printer that reproduces a digital image by propelling variably-sized droplets of liquid or molten material (ink) onto a page.

• Laser - Is a common type of printer that rapidly produces high quality text and graphics on plain paper.

• Line Printer - Is a form of high speed impact printer in which one line of type is printed at a time.

• Plotters - Is a vector graphics printing device to print graphical plots, that connects to a computer.

• Sound Card - Is a computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs.

• Speaker - An output device that produce sound.

STORGE DEVICES

Primary Memory

Storage Capacity - Limited

Volatile Memory

Primary Devices : RAM, ROM

Secondary Memory

Storage Capacity – Larger

Non-Volatile Memory

Secondary Devices : Floppy Disk, Hard Disk

Storage Devices • Magnetic Tape, Cartridge Tape - Storage Medium that

is accessed and processed sequentially. Advantages: Low cost, Portable. Disadvantages: Slow, no direct process, must be labeled, environment problem.

• Hard disk drives - Non-volatile storage device. Advantages : Unlimited Storage Capacity, Direct Access, Portable, High data transfer rate, less vulnerable to data corruption. Disadvantages : Expensive

• Floppy Disks - A data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. Advantages: Low cost, Portable, easy to use. Disadvantages: Unreliability

• CD - A Compact Disc (CD) is an optical disc used to store digital data. Advantages: Low cost, Portable. Disadvantages: Limited space

• VCD - Is a standard digital format for storing video on a Compact Disc. Advantages: Low cost, Portable. Disadvantages: Limited space.

• CD-RW - A rewritable optical disc format used to store digital data.

• Zip Drive - Is a medium-capacity removable disk storage system

• DVD - Also known as Digital Versatile Disc or Digital Video Disc, is an optical disc storage media format. Its main uses are video and data storage.

• DVD-RW - Is a rewritable optical disc.

Software Is a general term primarily used for digitally

stored data such as computer programs and other kinds of information read and written by computers.

• System Software - Computer software designed to operate the computer hardware and to provide and maintain a platform for running application. software.

• Application Software - Computer software designed to help the user perform a particular task.

Operating System (OS) Operating System acts as an interface between

hardware and user. It is responsible for the management and coordination of activities and the sharing of the resources of a computer.

• Single user OS - Usable by a single user at a time.• Multi user OS - The operating systems of this type

allow a multiple users to access a computer system concurrently.

• Real time OS - It is a multitasking operating system that aims at executing real-time applications using specialized scheduling algorithms.

• Timesharing OS - Is sharing a computing resource among many users by means of multiprogramming and multi-tasking By allowing a large number of users to interact concurrently with a single computer

• Batch processing OS - Execution of a series of programs ("jobs") on a computer without manual intervention.

• Multiprocessing OS - Use of two or more central processing units (CPUs) within a single computer system.

• Multiprogramming OS - Allocation of a computer system and its resources to more than one concurrent application, job or user.

• Multitasking OS - A method by which multiple tasks, also known as processes, share common processing resources such as a CPU.

• Distributed processing - Distributed processing implies that processing will occur on more than one processor in order to complete a transaction.

Programming Language• A programming language is an artificial language that can

be used to instruct a computer to do a particular task. • Machine Language : Machine language is the language of

'0' and '1' which is actually understood by the machine and thus no translator is required. But is not in readable form for human being.

• A programming language is an artificial language that can be used to instruct a computer to do a particular task.

• Machine Language : Machine language is the language of '0' and '1' which is actually understood by the machine and thus no translator is required. But is not in readable form for human being.

• Assembly Language : Assembly Language is language which is in symbolic codes for ex. If instruction of adding two numbers has to be written 'ADD' symbol can be used in this program can be written. Thus assembly language are a little easier to code for human beings but a program called assembler is needed to translate this symbolic code in machine code.

• High Level Languages : High level languages are in easily readable form and a program called compiler is used to translate the program into machine code.

• Compiler : It is a translator program which is used to translate high level language program to machine language program. Thus high level language program acts as input for the compiler and the machine language comes as output from it. After compilation of the source program, the resulting object program is saved for further use, and thus repeated compilation is not necessary

• Interpreter : It is also a type of translator program. Unlike Compiler, which gives a machine code program as a result, Interpreter only results in execution of program if program's syntax is right but since the resultant object program is not saved for further use thus interpreter is needed every time the program is run.

Interpreter takes one statement of source program, translates it into object program instruction and then immediately executes the resulting machine language instruction while compiler translates the entire source program into object program and is then not involved into the execution.

Assembler : Assembler is a translator program which translates assembly language program into machine

language program. Along with translating, it also assembles the machine language program in the main memory of the

computer and thus make it ready for the execution.

Compiler• Scans complete

program and then translate it into machine code

• When all the syntax errors are removed, only then program can be executed

• Slow Debugging• Fast Execution

Interpreter• Scan a single line,

translate it, and then move to the next line

• Every line is checked for the syntax error and then translated into the machine code

• Fast Debugging• Slow Execution