Computer Concept NOTES, Cheat Sheet of Computer science

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Computer Concepts

INTRODUCTION

A computer is a programmable device which responds to a specific set of instructions in a well-­‐ defined manner and executes a prerecorded list of instructions. A computer is an electronic device which takes input from the user, processes it, stores it and gives output in desired form. The computer as a system is a combination of hardware and software components that jointly offer the necessary services to the user. Computer is derived from the Latin word ‘ Computare ’ which means ‘to calculate’. CHARACTERISTICS OF COMPUTERS

1. Speed : The speed of computer for performing a single operation can be measured in terms of Milliseconds, Microseconds, Nanoseconds and Picoseconds. 1 /1000 or (10-­‐^3 ) sec……………………………..1 Millisecond (ms) 1/1000000 or (10-­‐^6 ) sec………………………....1 Microsecond (μs) 1/1000000000 or (10-­‐^9 ) sec …………………….1 Nanosecond (ns) 1/000000000000 or (10-­‐^12 ) sec…………………1 Picosecond (ps) 1/000000000000000 or (10-­‐^15 ) sec……………..1 Femtosecond (fm) 2. Storage : The storing capacity is measured in terms of Bytes, Kilobytes, Megabytes, Gigabytes and Terabytes. 4 bits………………………..................................1 Nibble 8 bits………………………..................................1 Byte 1024 Bytes ............................................................1 Kilobyte (KB) 1024 Kilobytes.......................................................1 Megabyte (MB) 1024 Megabytes.....................................................1 Gigabyte (GB) 1024 Gigabytes .....................................................1 Terabyte (TB) 3. Accuracy and Reliability : Computer can perform all the calculations and comparisons accurately. Sometimes, errors may be produced by computers due to the fault in the machine or due to mistakes in the programs. If the input data are not correct, this may also lead to incorrect output. 4. Automatic: Computers is an automatic machine. Everything that is given to computer are processed and done by computer automatically according to the instruction provided. 5. Versatility : Computer has a wide range of application areas i.e., computer can do many types of jobs. It can perform operations ranging from simple mathematical calculations to highly complex and logical evaluations for any extended period of time. Some of the application areas of computers are Education, Science and Technology, Business, Medicine, Astronomy etc. 6. Diligence : A computer can perform repetitive tasks without being bored, tired and losing concentration. It can continuously work for several hours without human intervention after the

4. Desktop Publishing System: A desktop publishing package is more powerful, attractive and efficient than word processor package. The system includes computer and a number of peripherals with powerful software that can produce various layouts with pictures and text printed in a variety of attractive way, which are used in manuals, bulletins, newsletters etc. 5. Education: Computers are used as teaching aid, information resource, and computing and research tool. When computer is used as a teaching aid, it is referred to as Computer Assisted Instruction (CAI). Software for CAI can be prepared in a variety of modes, such as tutorial, discovery, problem solving, modeling, and drilling and practice modes. 6. Health and Medical Field: Computers are widely used in hospitals to help doctors in diagnosis, getting information on patients, diseases, treatment, drugs, keeping patient’s record etc. Examples: Magnetic Resonance Imaging (MRI), CT scan machine, Eye testing machines, Ultrasonic machine, etc. 7. Home: Home computers can be used in recreational activities. Home computers can also be used in storing personal information such as birth dates, addresses, telephone numbers, photo albums, to keep the record of family expenses etc. People use home computers to listen songs, watching movies, accessing the Internet, etc. 8. Industries: Computers are extensively used in industries for automatic control of machines, process, measurement and display of electrical and physical quantities. 9. Military: Smart weapons use microprocessor-­‐based control systems. Modern tanks, torpedoes, missiles etc. employ computerized control systems. A guided missile uses internal computer for its control. 10. Multimedia: In recording and film studio computer are used intensively. The music can be recorder in different tracks and later merge to a single music. Movie editing can be done frame by frame. 11. Office: Computers are used in preparing reports, memorandum, and copy of advertisement, letter, publicity, contracts, forms, notes, and notices etc., which are the basic works of an office. Computer helps user in preparing, storing, retrieving and displaying text. In offices accounting, billing preparation of payrolls, data analysis, auditing, investment, inventory control, preparation of budgets, sales analysis etc. are also performed. In most of the computerized offices, word processing and spread applications are used. 12. Research: Scientific and engineering design and research work involve complex and massive computations. So computers are must for this type of work. 13. Simulation: Computer simulation involves typing to predict what will happen in a real-­‐life situation from model of that situation. Computer Aided Design (CAD) is widely used in the design of electronic circuits, ships, roads cars etc.

HISTORY OF COMPUTERS

The computer, which is one of the most advanced discoveries of mankind, has got a long history. Around 3000 years before the birth of Jesus Christ, there were no any kinds of number system. So, people had to remember a lot of information. They felt the need to count the things. Then they started counting using their fingers. But the limited number of fingers had made it difficult for them to remember more facts. So, they used stones for counting or they made scratches on wall or tied knots in a rope. The history of computer is classified on the basis of age as follows:

1. Age of Mechanical Calculators
2. Age of Electromechanical Computers
3. Age of Electronic Computers 1) AGE OF MECHANICAL CALCULATORS a. Abacus : It is manual calculating device. Basically an abacus consists of wires having pebbles or beads. The frame consists of two parts upper & lower. The upper part is called ‘ heaven ’ whereas lower part is called ‘ earth ’. The heaven consists of two beads whereas the earth part consists of five beads to each wire. The value of a bead on heaven part is five & one in earth part. Each abacus consists of eleven wires. Its exact origin is unknown. It may have originated in china, Egypt or Greece. Fig: Abacus b. Pascal’s Calculator: In 1642, French mathematician Blaise Pascal invented the first real calculating machine that could add and subtract numbers quickly, which was named as Pascal’s Calculator or Pascaline. It consists of numbered toothed wheels, each wheel having numbers from 0 to 9. A complete turning of first Wheel causes the 2nd wheel to move the next number. It has a simple monitor to see the result, too. Calculation including addition and subtraction was possible up to 8 digits, which was a great achievement at that time. The disadvantage of this machine was that it could not carry out multiplication and divisions.

minute. So, Hollerith’s punched cards method become very popular and widely used. In 1896, he established the Tabulating Machine Company to make and sell his invention. Later in 1923, this firm merged with other companies to form the IBM Corporation, which is the most popular and biggest company in computer manufacturing. 2) AGE OF ELECTROMECHANICAL COMPUTERS f. Mark–I: In 1937, Harvard professor, Howard Aiken, constructed an electromechanical computer named Mark-­‐I (also known as Automatic Sequence Controlled Calculator), which could perform according to pre-­‐programmed instruction automatically. Thus it is also called the first computer. It was based on Charles Babbage’s principle after 100 years of his death. Although it was very huge with dimension 51 ft. long, 8 ft. height and 3ft. wide using 18,000 vacuum tubes (electronic) with 7 lakhs 50 thousands parts, it was the milestone in history of computer. In 1944, Howard Aiken modified Mark-­‐I and invented Mark-­‐II, which used 19000 valves. Fig: Mark I g. ABC (Atanasoff Berry Computer): In 1938, John Atanasoff and Clifford Berry designed ABC (Atanasoff Berry Computer) for solving systems of simultaneous equation. It used 18000 valves and other 45 valves for internal logic and capacitors for storage of electrical charges. It used punched cards as secondary storage. 3) AGE OF ELECTRONIC COMPUTERS h. John Von Neumann: In 1944, Hungarian mathematician, Jon von Neumann gave the ideas: Computer instruction as well as the data being manipulated could be stored internally in the machine. So he is called the “ father of stored program ”. Before that, program required for the computer were integrated and written permanently in chips, so modification of program was not possible. But after Neumann, such programs were stored inside computer in some storage media, so modification was easy and flexible. i. ENIAC (Electronic Numerical Integrator and Calculator): In 1946, J. Presper Eckert and John W. Mauchly developed ENIAC. At that time ENIAC was the largest single electronic apparatus in the world. It was a large-­‐scale, general-­‐purpose digital electronic computer built from 17468 vacuum

tubes. It was the first and last computer, which used decimal number system instead of binary system. Fig: ENIAC j. EDSAC (Electronic Delay Storage Automatic Computer): It was invented by Maurice Wilkes in

1949. It also used vacuum tubes. Although started after EDVAC, it was completed before EDVAC. So, it became the first stored program computer. k. EDVAC (Electronic Discrete Variable Automatic Computer): It was developed by J. P. Eckert and J. Mauchly in 1952. Although started before, it was completed after EDSAC. It also used vacuum tubes and some internal storage. Fig: EDVAC l. UNIVAC (Universal Automatic Computer): It was developed by J. P. Eckert and J. Mauchly in
1950. It was the first computer manufactured for commercial use and general purpose digital computer. Before this, all the computers were either for defenses or census.

Examples: Mark-­‐I, EDVAC (Electronic Discrete Variable Computer), EDSAC (Electronic Delay Storage Automatic Computer), UNIVAC (Universal Automatic computer). SECOND GENERATION (1956-­‐1963) Second generation of the computer started after the invention of transistors. John Bardeen, Walter Brattain and William Shockley invented the transistor in 1947 at Bell Laboratory. There are two kinds of transistors, the bipolar transistor (also called the junction transistor) and the field effect transistor (FET). All computers, which use transistors as memory device, are categorized as second-­‐generation computer. Characteristics:

1. Transistors were smaller, faster, occupied less space and higher reliable compared to vacuum tubes. One transistor can do the tasks of 1,000 vacuum tubes. 2. Transistors required less electricity and emitted less heat than vacuum tubes. 3. Magnetic cores were developed for primary storage and magnetic tape and magnetic disk for secondary storage. 4. Second-­‐generation computer replaced machine language with assembly language (abbreviated or mnemonic form) to replace long difficult binary codes for giving instructions. 5. High level languages such as COBOL (Common Business Oriented Language) and FORTRAN (Formula Translator) came in common use during this time. 6. The operating speed was increased up to the microseconds range. Examples : The examples of the second-­‐generation computers are IBM 1401, IBM 1600, 7070, 7080, 7080, and ICL 1950/10 and Honey well 400 series. THIRD GENERATION (1963 – 1971) The third generation computers replaced transistors with “ Integrated circuits (IC) ” popularly known as chips. An IC is an electronic circuit with a large number of components (many transistors, resistors and capacitors) built on a small silicon chip. The third generation computer use SSI (Small Scale Integration) and MSI (Medium Scale Integration) circuits for internal operations. Characteristics: 1. Using ICs proved to be highly reliable, relatively inexpensive and faster. 2. Less human labor was required at assembly stage. 3. Operation speed increased beyond nanoseconds. 4. Computers became portable. They were smaller in size but had high memory. 5. The computer used programming languages such as Pascal and FORTRAN.

Example: IBM 360 series, IBM 370 series, ICL 1900 series, ICL 2900, UNIVAC 9000 FOURTH GENERATION (1971-­‐PRESENT) The fourth generation computer use LSI (large Scale Integration) and VLSI (Very large Scale Integration) circuits for internal operations. VLSI has squeezed hundreds of LSI (1000 transistors) onto a single chip. Characteristics:

1. Highly accurate and totally reliable. 2. Operation speed increased beyond Picoseconds and MIPS (Million of Instruction per Seconds) 3. This chip reduced the physical size of the computer and increased their power. 4. Magnetic and optical storage devices. Examples: IBM PC, Apple/ Macintosh, Wang Laser, Letron etc. FIFTH GENERATION (FUTURE GENERATION) The fifth generation computer will use AI (Artificial Intelligence) and be based on advances in silicon technology, i.e. Gallium Arsenide (GaAs) termed as super-­‐ conductor or bio-­‐ chips. Scientists are now at work on these computers. Characteristics: 1. They will be able to understand natural language, speak command, capacity to see their surrounding and will have thinking power called Artificial Intelligence (AI). 2. In contrast to present DIPS/LIPS (Data/Logic Information Processing System), the 5th^ generation computer will have KIPS (knowledge Information Processing System) 3. It will support parallel processing in full fledge. Examples: There are different programs under way to develop fifth generation computer.

• ICOT program in Japan.
• MCC and DARPA project of USA.
• Alvey project of UK.
• The famous 5th generation computer is fictional HAL9000. COLOSSUS MACHINE The Colossus machines were electronic computing devices used by British codebreakers to read encrypted German messages during World War II. These were the worlds first programmable (if not fully) digital electronic computing devices. Colossus used state-­‐of-­‐the-­‐art vacuum tubes (thermionic valves), thyratrons and photomultipliers to optically read a paper tape and then applied a programmable logical function to every character, counting how often this function returned "true". Although machines with many valves were known to have high failure rates, it was recognised that valve failures occurred most frequently with the current surge at power on, so the Colossus machines, once turned on, were never powered down unless they malfunctioned.

components) that has been manufactured in the surface of a thin substrate of semiconductor material. SSI, MSI, LSI, VLSI, ULSI The first integrated circuits contained only a few transistors. Called "Small-­‐Scale Integration" (SSI), they used circuits containing transistors numbering in the tens. The next step in the development of integrated circuits, taken in the late 1960s, introduced devices which contained hundreds of transistors on each chip, called "Medium-­‐Scale Integration" (MSI). Further development, driven by the same economic factors, led to "Large-­‐Scale Integration" (LSI) in the mid 1970s, with tens of thousands of transistors per chip. The final step in the development process, starting in the 1980s and continuing through the present, was "Very Large-­‐Scale Integration" (VLSI). This could be said to start with hundreds of thousands of transistors in the early 1980s, and continues beyond several hundred million transistors as of 2007. To reflect further growth of the complexity, the term ULSI that stands for "Ultra-­‐Large Scale Integration" was proposed for chips of complexity of more than 1 million transistors. MICROPROCESSOR A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). The microprocessor was born by reducing the word size of the CPU from 32 bits to 4 bits, so that the transistors of its logic circuits would fit onto a single part. One or more microprocessors typically serve as the CPU in a computer system, embedded system, or handheld device. COMPUTER SYSTEM Computer System is a group of physical parts that are integrated to achieve the objectives. A complete computer system consists of 4 parts: hardware, software, people, and data. A computer system needs to do the following operations: Ø Input: i.e. to accept the data/instructions from users Ø Process: i.e. to process the data Ø Storage: i.e. to store or holds the data Ø Output: i.e. to provide the final result to users. This cycle of operation of a computer is referred as Input-­‐Process-­‐Output or IPO cycle.

COMPUTER ARCHITECTURE

Every computer is constructed by combining various parts. All these parts work in an organized way to perform calculations, organize data, and communicate with other computer systems. The design, arrangement, construction or organization of the different parts of a computer system is called as “ computer architecture ”. Computer system architecture (Anatomy) is concerned with the structure of computer. In other words, the style of construction & organization of many parts of the computer system is called as “computer architecture”. Computer System Architecture consists of the various components such as: Ø Input Unit Ø Central Processing Unit (CPU) Ø Memory Unit (MU) Ø Output Unit Fig: Block diagram of computer system architecture HARDWARE AND SOFTWARE Hardware refers to all the physical parts that make up a computer. That is, all the electric, electronic, and mechanical devices of the computer are hardware. Examples of hardware are keyboard, mouse, monitor, and printer. So, hardware is those parts of the computer, which we can touch. Software is a set of electronic instructions that make computer perform tasks. In other words, software tells the hardware what to do. Without software, hardware is useless. Hardware needs instructions to process data into information. Those instructions are supplied from software. Software is also referred to as a set of program. Computer uses varieties of programs. Some programs are developed for computer’s own use and internal maintenance. Other types of programs are used for calculating and processing data.

CPU

ALU

CU

Input Unit Output Unit

Primary Memory

Secondary Memory

completes, the data is again transferred back into the memory unit. This transfer of data from the memory unit to the ALU and vice-­‐versa is also done under the directions of the control unit. Main functions of the ALU are given below. § Carries out arithmetic operations such as addition, subtraction, multiplication, and division § Performs logical operations such as comparison among data (equal to, greater than, less than and not equal to). § Works under the direction of the control unit b. Control Unit (CU) Control unit is the most vital part of the CPU. It reads every instruction stored into the memory. There after, it issues control signals necessary to execute the instruction. The control unit, actually, ensures that every instruction is read, understood, and executed in sequence. The CU coordinates and controls all the parts of the computer. It is the nerve center of the computer. It coordinates and controls the interpretation, flow and manipulation of all data and information. It also controls the flow of data from input devices to memory and from memory to output device. Main functions of the Control Unit are as hereunder. § Receives inputs send by input device, and store them into memory unit § Bring instruction from the memory unit, and decode the instruction (interpret what the instruction is saying) § Controls movement of data in and out of the ALU. § Directs the ALU to process data § Control the movement of data and instruction in and out of the memory unit § Controls movement of processed data (information) to output device § Directs output device to produce information § Directs and controls reading and writing of data on storage unit CACHE MEMORY In computer, data moves between RAM and the CPU frequently. In fact, RAM is very much slower than the CPU. Hence, moving data between RAM and the CPU is a time consuming process. It makes the CPU often idle and waiting for data. A solution to this problem is a special type of memory called cache memory (pronounced cash ). The cache memory (also called RAM cache ) exists between RAM and the CPU. A Cache memory is a high-­‐speed memory placed in between central processing unit (CPU) and RAM to increase the speed of processing. The speed of processor is faster than the RAM; hence the cache memory is used in between CPU and main memory (RAM) so that the speed of operation of main memory and cache memory together can meet the speed requirement of the high speed CPU.

The cache memory is very small, expensive and has high speed. Today’s PCs have 256 KB, 512 KB or even 1024 KB cache memory. Cache memory is generally built directly into the microprocessor chip. Actually, the cache memory stores only a few and frequently used data and instructions. When the CPU needs data, it first searches in the cache memory. If the data is not there, it searches RAM. This helps the CPU to work faster and increase processing speed. Below is the figure that shows how the cache memory works with the CPU and the main memory (RAM). REGISTERS Registers are primarily used to store data temporarily during the execution of a program. They are used as temporary memory locations in the sense that the information or data is held in them only for as long as it is necessary for one instruction. Registers can be of different sizes & capacities. Some registers are special purpose registers and some are general-­‐purpose registers. General purpose registers store data and intermediate results during the execution of a program. General-­‐ purpose registers are also accessible to programmer through instructions. Special purpose registers like PC (Program Counter) holds the address of the next instruction to be executed and SP (Stack Pointer) holds the address of the first location of the stack.

3. MEMORY UNIT (MU) Memory unit is the area, where the computer keeps programs, files, data, and instructions. All these things are only stored temporarily. Memory unit is built inside the computer, so it is also known as internal memory. The CPU needs data and instructions to operate the computer. These things must be stored in an area somewhere inside the computer. When data and programs are not in use, they must be kept permanently in another safe area. In computer, all these areas are called memory. Therefore, memory is the area in the computer, which holds data, instructions or programs. As input unit sends data or instructions, the computer at first keeps them into the memory unit. When the computer completes processing of data, it again keeps them into memory unit. When a user launches a program, it is also loaded into and run from memory unit. Thus memory unit is a space, which is allocated for temporary storage of data and programs. Memory is a part of computer (device) that is used to store data as well as instructions (programs). Physically, memory consists of chips either on the motherboard or on a small circuit board attached to the motherboard. Fig: Use of cache memory Main Memory Cache

CPU Memory

• Its cost is high.
• It is made up of flip flops and it stores the bit as a voltage.
• Speed is high.
• Produce more heat.
• Larger than DRAM Dynamic RAM (DRAM)
• It loses the stored information in a very short time even though the power supply is on.
• Cost of DRAM is less (low price)
• Made up of transistors and logic gates, and stores the bit as a charge.
• Speed is lower than SRAM.
• Produce less heat.
• Smaller than SRAM. 2 READ ONLY MEMORY (ROM) The read only memory (ROM) is a memory unit that performs the read operation only; it does not have write capabilities. The information stored in a ROM is made permanent during the hardware production and cannot be altered. ROMs are non-­‐volatile memory, i.e. information stored in ROM is not lost even if the power supply goes off. So, ROMs are used for storing the programs to boot the computer handling the operating system and monitor program controlling a machine. They are slower than RAM. Actually, the ROM is built and assembled in the motherboard. There are various types of ROM: a. PROM (Programmable Read Only Memory) b. EPROM (Erasable Programmable Read Only Memory) c. EEPROM (Electrically Erasable Programmable Read Only Memory) PROM (Programmable ROM) A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever and cannot be changed. They are manufactured as blank memory. 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. EPROM (Erasable Programmable ROM) EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light for 10 to 20 minutes. The ultra-­‐violet light clears its contents, making it possible to reprogram the memory. For erasing purpose, the EPROM chip has to be removed from computer. EEPROM (Electrically Erasable Programmable ROM) It is a special type of PROM that can be erased by exposing it to an electrical charge. The time required to erase this type of PROM is very short (few seconds). Unlike EPROM chips, EEPROMS do not need to be removed from the computer to be modified.

Fig: Types of memory

4. OUTPUT UNIT When the ALU completes processing, it returns back the data into memory unit. The memory unit, thereafter, transfers the processed data towards output unit. Finally, the output unit shows the processed data in suitable form. Thus, function of the output unit is to present processed data (information) in human -­‐readable form to the user. Computer uses different types of hardware to show information. All those hardware are called output devices. Every output device is capable of presenting information in user-­‐ understandable form. The most common output device is the monitor. Other output devices used in computer are printer and speaker. There are two types of output devices. Softcopy Output devices: Softcopy output refers to the output displayed on the screen. The output on the screen is lost when computer is turned off. The most common output device is monitor. Sound produced by voice output device (speaker) is also softcopy output.

MEMORY

Main Memory Secondary Memory Volatile Memory (RAM) Non-volatile Memory (ROM ) Optical Storage Magnetic Storage SRAM DRAM PROM EEPROM EPROM Disk Drum Tape Floppy Disk Hard disk CDROM CDR CDRW DVD