Fundamental of digital computer

Transcription

1 Introduction to computer:- Fundamental of digital computer A computer is an electronic device that has the ability to accept data, store data, perform mathematical and logical operations, and report the results. Computers have become an integral part of our lives today. Many aspects of our life have been affected by the changes brought by computer. Today Banks, Educational institutions, railways and airline reservations and commercial organizations use the computers to performing difficult and repetitive tasks. Computers are also used in the fields of weather forecast, medical research, security purpose, space research and undersea explorations. Computers are categories on the basic of size, cost and performance. The various types of computers are Microcomputers A small computer that contains a microprocessor and its central processor. Minicomputers A computer of medium power. Mainframe A large computer system with central processing unit. Supercomputer A powerful mainframe computer capable of dealing with complex problem (super computing) Hardware / Software: A computer system consists of hardware and software for its proper functioning. Hardware: The physical components of the computer are collectively called as hardware. Software: The computer requires a set of instruction to perform any task. These are called programs. A set of program is known as software (e.g. Operating System). Without OS the computer is not functioning. S/w can be classified into 2 types. I. System software II. Application software System software: System software s are used for an effective execution of user s program on the system. Application software: Application Software are used to satisfy the application need of the user. 1

2 Working principle of computer. The computer works on the principle of input process output. Input: Data and instructions must be fed into computer is known as input. This can be carried out with the help of the input devices. Keyboard, mouse, scanner, digital cameras, barcode reader, are the examples of input device. Process: The computer works on the data given according to the instruction is known as process. It is carried out by the central processing unit (CPU). Output: The results are the final output is carried out with the help of the output devices. Monitor and printer are examples of output devices. Block diagram of computer: The central processing unit is known as the brain of the computer. It is the controller of a computer. It has 3 components. Arithmetic logic unit (ALU) the ALU perform Arithmetic and Logic operations, and other data processing tasks as specified by a program. Control Unit (CU) It controls the entire processing. It monitors and guides the flow of information between various units. The control unit receives the instruction one by one form the program which is stored in memory. Memory Unit (MU) The memory unit stored program as well as input, output and intermediate data. The memory of a computer is a working place where it temporarily keeps information and data to help in its calculation. 2

3 Characteristic of computer. Computers perform a variety of activity with reliability, accuracy and speed. These characteristic of computer make them so popular and widely used. Speed: Computer is an electronic device that operate on electric signal, which travel at the speed of light. The quick service offered by computer in various field depends on its speeds. The speed of the computer is measured in millisecond, microsecond, nanosecond and picoseconds where Millisecond=1/1000 second (or) 10-3 Microsecond= 1/1,000,000 second (or) 10-6 Nanosecond=1/1000,000,000 second (or) 10-9 Pico second=1/1000,000,000,000 second (or) Storage capacity: Computer has enormous storage capacity. They can store large volumes of data for quick retrieval. The storage capacity of a computer depends on its memory and is measured in bits, bytes, kilobytes, mega bytes, giga bytes and tera byte where 8 bits= 1 byte 1024 Byte = 1 Kilo Byte (KB) 1024 Kilo byte = 1 Mega Byte (MB) 1024 Mega byte=1 Giga Byte (GB) 1024 Giga byte= 1 Tera Byte (TB) Accuracy: Computers are not only fast but also accurate. The qualities user of the computer is made possible by the capability of its accuracy. Data stored in a computer can be updated as when required. The accuracy in the ratio corrects information to the total amount of information. 3

4 Memory: The memory of a computer is a working place where it temporarily keeps information and data to help in its calculations. The computer makes use of Internal Memory (primary) External Memory on storage medium (Secondary) Internal Memory: It is the memory that built within the computer. It is also called as a main memory. Its classified into two types. ROM: Read Only memory (ROM) Random Access Memory (RAM) In this memory, information once stored in permanent. Its can only be read and not written onto. It contains a set of start-up-instructions that are to be performed when a computer is turned on. The contents of the ROM are not erased if the power is switched off. RAM: This is the computer internal memory that can be read and written onto. RAM is the area used by the CPU during the calculations and processing. The contents of the RAM are erased if the power is switched off. External Memory: It also called as external storage device. Storage device is a medium to store the information that you want. These devices are used to transfer data from one device to anther device. It is necessary to store the data, programs and instruction to use them later. The secondary storage device can be classified depending on the characteristic of the medium. They are 4

5 1) Sequential - access- storage device: Magnetic tapes are example of sequential access storage. Records are organized and accessed one after the other. Large volume of data can be stored in magnetic tape but it is slower in speed for data retrieval. If we want to access the n-th record n-1 records must be passed through. Suppose if we want to access the 100 th record first 99 should be passed through. It is used for off-line applications. 2) Direct- Access- storage device: Floppy disks and hard disk are the example for direct access storage device. The storage and retrieval of data is at a higher rate. The data is randomly accessible and this makes the device suitable for on-line application. 3) Magnetic disks: The disks are flat circular plats coated on both sides with iron-oxide magnetized material. It is available in 2 form the floppy disks and the hard disks. Floppies are flat circular plastic disk coated on both sides with magnetic material. Hard disks are groups of flat, circular flexible disks arranged vertically on a spindle. They are coated with magnetized material on both sides. Processors: Processors are program that translate the high-level language to machine language. The language processors are compiler, interpreted and assembler. Interpreted: This is an alternative to the compiler. Each statement of a program is converted into machine code, as it is needed during the execution of the program. The object code is not saved for future use. Assembler: The job of the assembler is to convert assembly language program into machine code. It also allocates areas of main storage. It produces a copy of the translated program on disk. 5

6 Compiler: Compiler is also a system software that will convert the program written in the high level language into its equivalent low level language. The program given in high level language is called source program. The program in low level language is called as object program. It is illustrate in the following diagram. Source Code High level Language Compiler (Translate) Object Code Machine Language Computer language: Computer or programming language is communicative system between the user and the computer. Program is a set of instruction to perform specific task. Types of computer language: There are 3 type of programming languages are, 1. Machine language (low level language) 2. Assembly language (using mnemonic code) 3. High level language (keywords) Machine language: Machine language is also called as low level language. It has only binary numbers (0 & 1). The computers can execute a program written using binary digits only. This type of programs is called machine language programs. It will be very difficult for developing programs for complex problem solving. Also it will be very difficult for a person to understand a machine language program written by another person. At present, computer user do not write programs using machine language. Also these programs written for execution in one computer cannot be used on another type of computer. That is the programs were machine dependent. 6

7 Assembly language: Assembly language has mnemonic (symbolic name) which is particular for a processor. Mnemonic codes are used to develop program for problem solving. The program below shows an assembly language program to add two numbers A and B. Mnemonic code Description MVI A, O5 - It reads the value of A MVI B, 04 - It reads the value of B ADD B - Add the value of A and B and store the result in A STA M - Move the result to Memory HLT - Stop the execution Assembly language is designed mainly to replace each machine code with an understandable mnemonic code. To execute an assembly language program it should first be translate into an equivalent machine language program. Writing and understanding programs in assembly language is easier than that of machine language. High level language: o High level language is a machine independent language. It has keywords. High level language permits the user to use understandable code using the language structure. In order to execute a high-level language program, it should be translated into a machine language either using a compiler or interpreter. The high level languages commonly used are BASIC - Beginner s All Purpose Symbolic Instruction Code FORTRAN FORmula TRANslation COBOL COmmon Business Oriented Language. After 1970 s the programming language such as C, C++. Visual Basic and Visual C++ are developed to make off line application. Recently developed programming language such as JAVA, JSP, and ASP.NET are suitable for developing on line application. Now this online programming language popular in IT industries. 7

8 The following program written in BASIC language is to add two given number. Program code Description 10 INPUT A, B - To read the value of A and B 20 LET C = A+B - A and B are added and result is stored in C 30 PRINT C - Print the value of c to monitor 40 END - Stop the execution Operating System Introduction : An operating system in a program that acts as an intermediary between the users of a computer and the computer hardware. The primary goal of operating systems are designed to be convenient, efficient and combination of these two. An operating system plays a vital role in every computer system. A computer system can be divided into four components. They are the hardware, the operating system, the application program and the users. The following figure shows the Abstract view of the components of a computer system. 8

9 The hardware provides the basic computing resources such as CPU, memory and I/O device. The application programs define the ways in which resources are to solve the computing problems to the user. (E.g. word processors, programming language, compiler and web browser) The operating system controls and co-ordinates the use of the hardware among the various application program for the various users. An operating system is similar to a government. Like a government, it performs no useful function by itself. It simply provides an environment within which other program can do useful work. Operating system can be explored form two view points. They are the user and the system view. User view The user view of the computer varies by the interface being used. The computer users sit in front of a PC. Consist of a monitor, keyboard, mouse and system unit. Such a system is designed for one user to utilize its resources. Some users sit at a terminal connected to a mainframe or minicomputer. Other users are accessing the same computer through other terminals. These users share resources and may exchange information. The operating system is designed to maximize resource utilization. Such as CPU time memory and I/O are used efficiently. Other users sit at workstations. Connected to networks of other workstations and servers. The operating system is designed to share resources such as networking and servers (file) computer and print. Recently many varieties of handhold computers have come into fashion. These devices are mostly standalone. Some are connected to networks, either directly by wire or through wireless modems. Due to power limitation they perform relatively few remote operations. The OS are designed mostly for individual usability, but performance per amount of battery life is important as well. Some computers have little or no user view. For e.g. embedded computers in home devices and automobiles may have a numeric keypad and may turn indicator lights on or off to show status. The operating systems are designed to run without user intervention. 9

10 System view From the computers point of view, the OS is the program that is most intimate with the hardware. An OS is a resource allocator. It allocates the required resource to solve a problem. The fundamental goal of computer systems is to execute user program and to make solving user problems easier. Toward this goal computer hardware is constructed. Since base hardware alone is not particularly easy to use. The OS includes the functions of controlling and allocating are developed. An operating system is the one program running at all times on the computer so it is called as kernel. Types of operating system: Mainframe computer systems were the first computer used to tackle many commercial and scientific applications. The growth of mainframe systems starts form Batch system to time shared systems. Batch System The user did not interact directly with the computer systems. Rather the user prepared a job, which consisted of the program, the data and some control information about the nature of the job and submitted it to the computer operator. The job was usually in the form of punch cards. After some times the output appeared. The output consists of the result of the program as well as a dump of the memory contents for debugging. The OS in these early computers was fairly simple. Its major task was to transfer control automatically from one job to the next. The OS was always resident in memory. The following figure shows the memory layout for a simple batch system. Operating System User Program 10

11 The operator collect the jobs form the programmers and sort it into batches with similar requirements and as the computer become available, would run each batch. The output from each job would be sent back to the appropriate programmer. In this execution environment, the CPU is often idle, because the speeds of the mechanical I/O device are slower than electronic devices. Multiprogrammed Systems: The introduction of disk technology allowed the OS to keep all jobs on a disk, rather than in a serial card reader. With direct access to several jobs the OS could perform job scheduling is the ability to multiprogramming. A single user cannot keep the CPU busy at all times. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. The OS keeps several jobs in memory simultaneously. The following figure shows the memory layout for a multiprogramming system OS 0 Job 1 Job 2 Job3 Job 4 512k This set of jobs is a subset of the jobs kept in the job pool. The OS picks and begins to execute one of the jobs in the memory. Eventually, the job may have to wait of some task. Such as an I/O operation to complete. In a non-multi programmed system, the CPU would sit idle. 11

12 In a multiprogramming system, the OS simply switches to and executes another job. When that job needs to wait, the CPU is switched to another job and soon. Eventually the first job finishes waiting and gets the CPU back. As long as at least one job needs to execute, the CPU is never idle. This OS is similar to lawyer. Time sharing systems: Time sharing system or multitasking is a logical extension of multiprogramming. The CPU executes multiple jobs by switching among them. A time sharing OS uses CPU scheduling and multiprogramming to provide each user with a small portion of a time shared computer. Each user has at least one separate program in memory. A program or process executes, it typically executes for only a short time before it either finishes or needs to perform I/O. I/O may be interactive i.e. output is to a display for the user and input is from a user keyboard or other device. Since interactive I/O typically runs at people speeds it may take a long time to complete. For e.g. the users can type maximum seven characters per second, but it is slow for computers. In this case the OS will rapidly switch the CPU to the program of some other user. Multiprocessor systems: Most systems to date are single-processor system they have only one main CPU. However multiprocessor systems also known as parallel or tightly coupled system are growing in importance. Such systems have more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral device. This system has 3 main advantages. Increase through put: By increasing the number of processors, we hope to get more work done is less time. The speed-up ratio with N processor is Not n rather it is less than N. Economy of scale: multiprocessor system can save more money then multiple single processor systems, because they can share peripherals, mass storage, and power supplies. Several programs operate on the same set of data, to store those data on one disk. 12

13 Increased reliability: if program can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down. If we have ten processors and one fails, then each of the remaining nine processors must pick up a share of the work of the failed processors. These systems are designed for fault tolerant. Multiprocessor systems can be classified into two types. Symmetric Multiprocessing (SMP) and Asymmetric Multiprocessing. Symmetric Multiprocessing: The most common multiple processor systems now use symmetric multiprocessing, in which each processor runs an identical copy of the OS and these copies communicate with one another as needed. (OS supports for SMP are Windows NT, Solaris, UNIX, and LINUX.) Asymmetric Multiprocessing: Some system use asymmetric multiprocessing, in which each processor is assigned a specific task. A master processor controls the system. The other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processor. Distributed Systems A network is a communication path between two or more system. Distributed system depends on networking for their functionality (to share computational tasks). Networks vary by the protocols used, the distances between nodes and the transport media. Most OSs support TCP/IP, including windows and UNIX operating system. These are 3 types of Networks. LAN - Exists within a room, a floor or a building. WAN - A global company may have WAN to connect its offices, world wide. These network OS includes one or several protocol. MAN - could link buildings within a city 13

14 a) Client server Systems: Terminals connected to centralized systems are now being supplanted by PCs. Today centralized systems act as server systems to satisfy requests generated by client systems. The following fig shows the general structure of a client sever system. Server system can be broadly classified as compute servers and file servers. Compute server system: Provide an interface to which clients can send requests to perform an action, in response to which they execute the action and send back results to the client. File-Server Systems: provides a file-system interface where clients can create, update, read and delete files. Real Time Systems: Another form of a special purpose OS is the real-time System. Sensors being data to the computer. The computer must analyze the data and modify the sensor inputs. Systems that control scientific experiments, medical imaging systems, industrial control systems and certain display systems are real-time systems. A real-time has well defined, fixed time constraints. Processing must be done with in defined constraints or the system will fail. 14

15 Real-time systems come into 2 flavors. They are Hard and soft real - time system. A hard real time system guarantees that critical tasks be completed on time. A soft real-time system, where a critical real-time take gets priority over other tasks, and retains that priority until it completed. Generation of Computer: The division of computer system into generation is determined by the device technology, system architecture, processing mode and language used. We consider each generation to have a time span of about 10 years. Adjacent generations may overlap in several years. We are currently in fourth generation while the fifth generation is not yet fully materialized. In 1833, prof. Charles Babbage, the father of the computer, developed a machine called Analytical engine which was base for the modern digital computer. The first Generation ( ) The introduction of the first electronic analog computer in1938. The first electronic digital computer named Electronic Numerical Integrator and computer was introduced in ENIAC is the first generation of computers. Electromechanical relays (A device activating changes in an electric circuit) were used as switching devices in the 1940s and Vacuum tubes (tube has Vacuum for the free passing of electric current) were used in the 1950s.These devices where inter-connected by insulated wires. Only binary coded machine language was used in early computers. In 1950, the first stored program computers was developed. This masked the beginning of the use of system software to relieve the user s burden in low-level programming. In 1952, IBM had announced its 701 electronic calculators. The system used William s tube memory, magnetic drum and magnetic tape, punched cards are used as a storage medium. 15

16 The second Generation ( ) Transistors were invented in Transistor is an electronic component used to control electric current and to provide amplification (amplify small voltage to large current). The first Transistorized digital computer TRADIC was built by Bell laboratories in transistors and diodes used in TRADIC. Primed (unity) circuits appeared (diode is a semiconductor it controls the flow of current in one direction having 2 terminals). Magnetic core memory was developed Assembly Language were used until the development of high-level languages FORTRAN in 1956 and ALGOL (Algorithmic language) in In 1959 COBOL was developed. Punched cards are used as a storage medium. The Third Generation ( ) This generation was masked by the use small scale integrated (SSI) and medium-scale integrated (MSI) circuits as the basic building blocks. Core memory was still used. High level languages were greatly enhanced with intelligent computer during this period. Multi programming was developed through time sharing operating systems. Virtual (computing is not physically existence but made by software appear to do) memory was developed. During this period, display units CRT (Cathode Ray Tube) and printers were used. The languages Pascal and C were developed. 16

17 The fourth Generation ( ) o The fourth generation computer to stress the use of large scale integrated (LSI) circuits for both logic and memory sections. o High level languages are being extended to handle both scalar (having only magnitude) and vector (both magnitude and direction) data. o In 1975 Bill gates and Paul Allen Found the Microsoft corporation to market Microsoft BASIC software written by them. o Today Microsoft is one of the leading software companies in the world. o In 1970 s IBM designed its first personal computer. Magnetic disks, floppy disks, and optical disks, were developed. o Bar code readers, magnetic ink character recognizer, optical readers were used. o Ink jet, laser printers, object oriented programming and expert system were developed. The FIFTH generation The fifth generation introduced a new era in the usage of computer Very high-speed machines were developed. Hard disk and RAMs with greater storage capacity were introduced to increase the efficiency and speed of the processing activities. Compact disks, DVD ROM s and optical disk replaced floppies. Devices such as mouse, light pen, touch screen, audio response systems were developed. 17