Instructor : Prof Saroj Kaushik Institure : IIT Delhi (CSE) cse.iitd.ernet.in Web Link :

Transcription

1 COL100: Introduction to Computers and Programming: Lecture 1: Introduction Instructor : Prof Saroj Kaushik Institure : IIT Delhi (CSE) saroj@ cse.iitd.ernet.in Web Link : Lecture Module 1

2 Course Contents Introduction to Computers, memory, ALU, CPU, I/O devices Data representations, Number System Conversion from one base to another Compliment representations of negative integers, Floating point representation Introduction to system software; operating systems, compilers and multi-user environments, Introduction to Computer Problem Solving, Fundamental algorithms, Program Design methods

3 Course Contents - Cont Concept of an algorithm; Algorithms to programs: specification, top-down development and stepwise refinement. Use of high level programming language for the systematic development of programs. Introduction to the design and implementation of correct, efficient and maintainable programs using some high level programming language Array techniques, Multidimensional arrays, Structured Data types, Merging, Sorting & searching, Dynamic Data structure algorithms using pointers, Functions & procedures & recursive algorithms, Introduction to Object oriented programming language (C++)

4 Books TEXT BOOKS R.G. Dromey, "How to Solve it by Computer", Prentice Hall of India, E Balagurusamy, "Programming in ANSI C", edition 2.1, Tata McGraw-Hill, reprint B.W. Kernighan & D.M. Ritchie, "The C Programming Language", Prentice Hall of India, N Barkakati, "Object-Oriented Programming in C++", Prentice Hall

5 Books Contd.. REFERENCE BOOKS Cooper,Mullish, "The Spirit of C", Jaico Publishing House, New Delhi, Richard Johnson-Baugh & Martin Kalin, "Application Programming in C", Macmillan International editions, Herbert Schildt, "The complete Reference C, Fourth Edition", Tata McGraw-Hill N. A. Solter and S. J. Kleper, Professional C++, Wiley India

6 Course Grading Structure These weights are indicative, and may change as semester progresses Minor 1 & 2, each with 15-20% weightage Major, 30-35% weightage Quizzes and home assignments, 5-10% weightage Programming exercises, 20-25% weightage

7 Lab Schedule Lab Schedule : Lab groups: E1 and E2 Lab sessions are primarily for learning coding of programs. Testing of programming skill will be tested and graded in labs only Labs will start from 13th August onwards E1 and E2 swap alternate week Lectures Sat- (10am-12pm) Sun (8-10am) Lab Gps Days Timings E1 Monday 1 pm - 4 pm E2 Saturday/ 3 pm - 5 pm Sunday 1 pm - 3 pm

8 Introduction to Computers

9 What is a Computer? Electronic device Capable of performing arithmetic operations on numbers logical operations on bits (binary digit) decision test retrieval, manipulation and storage of large amount of data at a very high speed

10 Generation of Computers Generation in computer terminology is a change in technology a computer is/was being used. Initially, the generation term was used to distinguish between varying hardware technologies. But nowadays, generation includes both hardware and software, which together make up an entire computer system. There are totally five computer generations known till date.

11 Summary of Generations Characteristics Gen I Gen II Gen III Gen IV Gen V Period till date Components Complexity of circuits Relative failure rate Languages used The Vacuum Tube One circuit component Transistors Few circuits components Integrated circuits circuits components LSI (Large Scale Integration Over 100 circuits components VLSI (Very large scale integration Over 1000 circuits components Very low Machine language Assembly language, FORTRAN, COBOL User oriented Languages Online commands Type of system Single user Single user Multi user Remote user Object oriented languages Remote user on internet

12 What Does A Computer Do? Computers can perform four general operations, which comprise the information processing cycle. Input Process Output Storage To do each of these computer has devices.

13 Devices that comprise a computer system Monitor (output) Speaker (output) System unit (processor, memory ) Printer (output) Storage devices Scanner (input) Keyboard (input) Mouse (input) (CD RW, Floppy, Hard disk, zip, ) 13

14 Why Is a Computer So Powerful? The ability to perform the information processing cycle with amazing speed. Reliability (low failure rate). Accuracy. Ability to store huge amounts of data and information. Ability to communicate with other computers. 14

15 By 1980, computers were classified into three main types. Main Frame: Traditionally large computers, often containing thousands of IC s and costing millions of dollars High speed, large storage & highly accurate can be shared by group of users Mini Computers: Types of Computers Smaller in size, slow in speed, low cost and can be shared by group of users Micro Computers (Personal computer (PC)): New class of general purpose machines intended for single users. Small in size and inexpensive

16 Contd Developments in microprocessor technology however means that today's desktop/laptops/tablets etc. Now a days microcomputer are available with more RAM and disk storage. The differences between mainframe, minicomputers and a desktop model may more likely be in the software that is being used as opposed to the hardware. For example, a multi-user operating system such as Unix, would typically be used, as opposed to the Windows systems of PCs in mainframe and minicomputer. Mainframe computers are still powerful machines (physically much smaller than their ancestors) with hundreds of megabytes of RAM and terabytes of disk storage. They have very powerful CPU's that allow them cope with large numbers of users. WorkStation It is also a single user computer system which is similar to personal computer but have more powerful microprocessor.

17 The following schematic diagram gives the layout of a digital computer.

18 The current architecture of PC (personal Computer) is as follows (major hardware components )

19 Contd.. The bus is a group of wires on the main circuit board of the computer through which electrical signal passes. It is a pathway for data flowing between components. Buses are of three types: Address bus: used to transmit address of memory location Data bus: Used to transmit data from/to memory Control bus: Supervises reading/writing of data Most devices are connected to the bus through a controller Controller coordinates the activities of the device and the bus.

20 Super Computer Supercomputer is the term used for the most powerful computer available at any time. These are typically tailored for very fast processing of what are known as number crunching applications. Such applications require a tremendous number of arithmetic calculations to be carried out. Weather forecasting is the classic example of such an application, where equations taking account of huge numbers of observations have to be solved. Other applications are to be found in astronomy and some branches of chemical analysis and modeling. Supercomputers at the moment can carry out trillions of operations per second! The Cray is perhaps the most well known supercomputer named after its designer, Seymour Cray.

21 How Does a Computer Know what to do? It must be given a detailed list of instructions, called a computer program or software, thattells what exactly it has to do. Before processing a specific job, the computer program corresponding to that job must be created and stored in memory. Once the program is stored in memory the computer can start the operation by executing the program instructions one after the other. 21

22 Computer System A computer system is made up of both Hardware electronic components Software Program consisting of set of instruction Example: Some of the Anology: Mobile is hardware and corresponding facilities available is software. CD is hardware and music on it is software.

23 Hardware Components Of A Computer? Input devices. Output devices. Central Processing Unit Memory. Storage devices.

24 The Keyboard The most commonly used input device is the keyboard on which data is entered by manually keying in or typing certain keys. A keyboard typically has 101 or 105 keys.

25 The Mouse Is a pointing device which is used to control the movement of a mouse pointer on the screen to make selections from the screen. A mouse has one to five buttons. The bottom of the mouse is flat and contains a mechanism that detects movement of the mouse.

26 Output Devices Output devices make the information resulting from the processing available for use. The two output devices more commonly used are the printer and the computer screen. The printer produces a hard copy of your output, and the computer screen produces a soft copy of your output.

27 The Central processing Unit, CPU The CPU contains electronic circuits that cause processing to occur. Does the `work of fetching, storing and manipulating values that are stored in the computers memory. It is considered the brain of the computer.

28 Main Components of CPU Arithmetic Logic Unit (ALU) The ALU carries out arithmetic operations (e.g. addition and subtraction) and logical operations (e.g. and, or, not) Control Unit (CU) The CU controls the execution of instructions.

29 CPU-Contd The processor as its name suggests is the unit that does the work of the computer system i.e. it executes computer programs. Instructions in the program tell the processor when and what to read from a keyboard; what to display on a screen; what to store and retrieve from a disk drive and so on. It can do arithmetic, compare numbers and perform input/output. (read information and display or store it). It has no magical powers. It is instructive to bear in mind that all computer programs are constructed from sequences of instructions based on such primitive operations.

30 Processor s speed The clock rate typically refers to the frequency at which CPU, is running and is used as an indicator of the processor's speed. It is measured in clock cycles per second or its equivalent, the SI unit hertz (Hz). The clock rate of the first generation of computers was measured in hertz or kilohertz (khz), In 21st century the speed of modern CPUs is commonly advertised in GigaHertz (GHz). Modern Computer performance is primarily affected by the processor and memory.

31 Memory Memory consists of electronic components that store data including numbers, characters, graphics and sound. It has different types of memory. Random Access Memory (RAM) Read only Memory (ROM) MROM (Masked ROM) PROM (Programmable Read only Memory) EPROM(Erasable and Programmable Read Only Memory)

32 Random Access Memory RAM RAM is where programs and data are kept during execution when the processor is actively using them. RAM is called Main memory or Primary memory. Main memory is: very closely connected to the processor. the contents are quickly and easily changed. holds the programs and data that the processor is actively working with. interacts with the processor millions of times per second.

33 RAM Contd RAM Is Volatile - temporary Has random access to any memory location Read & write access Program + data reside in this memory

34 Read only Memory - ROM Read only Memory (ROM) Non volatile Only read access Permanent programs reside

35 Types of Memory Contd.. MROM (Masked ROM) The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs which are inexpensive. PROM (Programmable Read only Memory) PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM program.

36 Types of Memory Contd.. EPROM(Erasable and Programmable Read Only Memory) The EPROM can be erased by exposing it to ultraviolet light for a duration of up to 40 minutes. During programming, an electrical charge is trapped in an insulated gate region. For erasing this charge, ultra-violet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.

37 Cache Memory A special and very high speed memory used to increase the speed of processing. Cache is sometimes called CPU cache Transfer from cache to CPU is very fast as compared to from main memory to CPU. Main Memory CPU ALU + CU Cache

38 Contd. It lies between CPU and main memory. The cache is usually filled from main memory when instructions or data are fetched into the CPU. Often the main memory will supply a wider data word to the cache than the CPU requires, to fill the cache more rapidly. It is expensive and usually small in size. Stores only segments of programs currently being executed by CPU. It is also sometimes called buffer.

39 Storage Devices- Secondary memory Connected to main memory The contents are easily changed, but this is very slow compared to main memory. It is used for long-term storage of programs and data. The processor only occasionally interacts with secondary memory. The most common types of secondary storage used are Hard disks CD-ROMdrives Flash Drives (USB, pen drives)

40 Hard Disk The hard disk has enormous storage capacity compared to main memory 300 times the amount of storage in main memory The hard disk is usually contained in the systems unit of a computer.

41 Reasons for having two types of storage Primary memory Secondary memory 1. Fast 2. Expensive 3. Low capacity 4. Connects directly to the processor 1. Slow 2. Cheap 3. Large capacity 4. Not connected directly to the processor

42 What is a Port A port is a physical docking point using which an external device can be connected to the computer. Information flows from a program to computer or over the internet using port.

43 Characteristics of a Port A port has the following characteristics: External devices are connected to a computer using cables and ports. Ports are slots on the motherboard into which a cable of external device is plugged in. Examples of external devices attached via ports are mouse, keyboard, monitor, microphone, speakers etc.

44 Data Representation in Memory Data is stored inside the memory in the form of 1 s and 0 s, Bits (Binary Digits) as shown below (ON/OFF positions). For example One byte consists of 8 bits.

45 Contd How many distinct values can be stored in one byte? Answer: 2 8 Minimum Value: Maximum value:

46 Organization of Main Memory Main memory consists of a very long list of bytes. In most modern computers, each byte has an address that is used to locate it. The picture shows a small part of main memory:

47 Contd Each row is called memory location that is a single byte and has an address. The addresses are the integers to the left of the boxes: 0, 1, 2, 3, 4, for location of one byte. The addresses for most computer memory start at 0 and go up in sequence until each byte has an address. The bits at a memory location are called the contents of that location. Each location contains a pattern of eight bits, each bit is either 0 or 1. When people say that a computer has "128 MB of RAM" they are talking about how big its main memory is.

48 Units of Memory 1 KB(1 KiloByte) contains 1024 Bytes. 1 MB(1 MegaByte) consists of 1024 KB. 1 GB(1 GigaByte) has 1024 MB. 1 TB (1 Terabyte consists of 1024 GB.

49 Table of units of measurement Name Equivalent Number of Bytes power of 2 Byte 8 bits Kilobyte 1024 bytes (KB) Megabyte 1024 KB 1,048, (MB) Gigabyte 1024 MB 1,073,741, (GB) Terabyte 1024 GB 1,099,511,627,

50 Software Computer programmers/users write the codes/ instructions that make-up software applications/programs. Set of instructions is also referred to as lines of code. Without software a computer is useless, just as a car without someone to drive it. To get a computer to perform a specific task, it must be given a sequence of unambiguous instructions called a program written in some programming language.

51 Types of Programs There are two categories of programs. Application programs (usually called just "applications") that people use to get their work done. Systems programs keep all the hardware and software running together smoothly. The difference between "application program" and "system program" is fuzzy. Often it is more a matter of marketing than of logic.

52 Application Programs Systems Programs Word processors Game programs Spreadsheets Data base packages Graphics programs Web browsers Operating system. Networking system. Database system. Compilers Web site server. Data backup.

53 Example of Types of Software Application Software Operating system Software

54 Operating Systems (OS) OS coordinates the operation of all the hardware and software components of the computer system. The operating system is responsible for starting application programs running and finding the resources that they need. When an application program is running, the operating system manages the details of the hardware for it. It is there in the background managing resources, doing input and output for the application, and keeping everything else running. The operating system is always present when the computer is running.

55 Resources managed by OS OS is a complex collection of many programs that governs the control of various resources such as: Processor Main Memory Secondary storage I/O devices Files The operating system is software; the same hardware can be used with many different operating systems (although only one at a time.)

56 Various Modules of OS There are various modules of OS Processor management Memory management Device management Information management These modules resolve conflicts, optimize performance and acts as an interface between the user s program and computer hardware. Modern operating systems usually come with a user interface that enables users to easily interact with application programs by using windows, buttons, menus, icons, the mouse, and the keyboard.

57 Examples of operating systems are DOS, Unix, Windows 98, Windows NT, Linux, Solaris, etc. There are different OS for different kinds of machines. Single user machine Batch processing Multiprogramming Time sharing Real time machines

58 Programming Languages Machine Lang Assembly Lang High level Lang Consists of 0 & 1 Pseudo inst English like insts Add 2 5 Input A, B Comp System Assembler translates Compiler translates directly executes it to M/L to M/L Difficult to write Simple to write Simpler to write Highly error prone Less error prone Lesser error prone Machine dependent Machine dependent Machine independent

59 Machine Language Consider machine of 16-bits Opcode (4-bits) Address (12-bits) There are 16 possible opcodes (Hypothetical example) Opcode Action 0000 Load accumulator (ACC)from memory 0001 Store accumulator in memory 0010 Add the contents of Acc with specified location and leave the result in ACC 1111 stop

60 M/L program Instructions Load ACC from Loc 10 Add ACC with contents of Loc 20 Store ACC contents in Loc 30 Stop Machine language

61 Assembly Language High level Language (pascal, C, C++, Java) Load Add Store Print Stop X Y Z Z Input X, Y Z = X+Y Output Z Stop One assembly instruction is equivalent to machine instruction One high level inst corresponds to many machine instruction

62 All CPUs have an instruction set (or language) that they understand. Eventually all assembly level / high level programs must be translated (or compiled) into instructions from this set. Roughly speaking, all processors have the same sort of instructions available to them. An executable program is machine language program that runs on a CPU and is always represented as a series of binary digits. This is achieved by compiling (translating) a high-level program with a special piece of software called a compiler. Compilers are incredibly complicated programs that accept other programs as input and generate a binary executable object file as output.

63 Types of Files The OS can take a program file, copy it into main memory, and start it running. supplies data files and its information to a running program when it asks. Last part of a file's name (the extension) shows what the file is expected to be used for. For example, "mydata.txt" the ".txt" means that the file is expected to be used as a collection of text, that is, characters. netscape.exe" the ".exe" means that the file is an "executable," that is, a program that is ready to run. "program1.py" the ".py" means that the file is a source program in the language PYTHON

64 Interpreter There are some language which are not compiled but interpreted by interpreter (Python, BASIC, SML, ). An interpreter is a program that acts like a processor that can directly execute a high level language. file_name.py Python Interpreter Processor Interpreting a Source Program

65 Here the source program file_name.py" has been written in Python (a programming language) by a programmer with a text editor i.e., gedit file_name.py. It is being interpreted by the PYTHON interpreter, which is running on the processor. The PYTHON interpreter will read each command in the source program and do what it says. When an interpreter is running a PYTHON source program, both the interpreter and the source program are in main memory. The interpreter consists of machine instructions that the hardware can execute directly.

66 Translator verses Interpreter Translator Takes a complete document in one language and creates a complete document in another language, which can then be used at any time. Translator is called compiler. Interpreter Acts as an intermediate between source language and machine language and converts instruction wise.

67 Compiler A source program is set of instructions written in a high level language.. It is translated into a machine language program by a system software called compiler. It takes a source file as input and produces an executable program (machine language program) as output.

68 Contd.. The source program is stored in a file created using a text editor. The source file is kept on the hard disk. When you have to run your program (Source program), first compile by compiler and form an executable file. The source file remains unchanged; a new executable file is created. The executable file is also kept on hard disk. Compilers are specific to high level languages (like "C") and a specific to processor type (like "Pentium"), and only runs under a specific operating system (like "Windows".) The above is what goes on with most languages: Ada, Pascal, C, C++, FORTRAN and others.

69 Example Problem : Consider the problem of converting F (Fahrenheit) to C (Centigrade) which is suitable for solution by computer. Formula: C = 5 * (F 32) / 9 Set of possible high level instructions: Input : F (given parameters) Output: C (output parameters) read F C = 5 * (F 32 ) / 9 print C end