Computer basics
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This document provides an overview of the key topics in computer science including data representation, computer hardware, software, algorithms, programming languages, and the history of computers. It introduces the von Neumann model which defines a computer as having four main subsystems: memory, arithmetic logic unit, control unit, and input/output. The model specifies that both programs and data are stored in memory and that programs are executed sequentially through instructions. The document then discusses the evolution of computer generations from mechanical to modern electronic computers based on this von Neumann model.
Computer basics
- 1. FOUNDATIONS OF COMPUTER SCIENCE 主讲：李艳 From Data Manipulation to Theory of Computation 云南农业大学
- 2. Book organization Computers and Data Computer Hardware Computer Software Data Organization Advanced Topics Chapter 1: Introduction Chapter 2: Data Representation Chapter 3: Number Representation Chapter 4: Operations on Bits Chapter 5: Computer Organization Chapter 6: Computer Network Chapter 7: Operating Systems Chapter 8: Algorithms Chapter 9: Programming Languages Chapter 10: Software Engineering Chapter 11: Data Structures Chapter 12: Abstract Data Types Chapter 13: File Structures Chapter 14: Databases Chapter 15: Data compression Chapter 16: Security Chapter 17: Theory of Computation
- 4. 1.1 THE COMPUTER AS A BLACK BOX DATA PROCESSOR You can think of a computer as a data processor. Using this definition, a computer acts as a black box that accepts input data, processes the data, and creates output data. Although this model can define the functionality of a computer today, it is too general. It is not clear how many types or sets of operations a machine based on this model can perform.
- 5. PROGRAMMABLE DATA PROCESSOR This model adds one extra element to the computer: the program. A program is a set of instructions written in a computer language that tells the computer what to do with data. In the new model, the output data depend on the combination of two factors: the input data and the program.
- 6. Same program, different input data
- 7. Same input data, different programs
- 8. 1.2 VON NEUMANN MODEL Every computer today is based on the von Neumann model. It is based on three ideas. FOUR SUBSYSTEMS The model defines a computer as four subsystems: memory, arithmetic logic unit, control unit, and input/output.
- 9. Memory Memory is the storage area. It is where programs and data are stored during processing. Arithmetic Logic Unit (ALU) The ALU is where calculation and logical operations take place. Control Unit The control unit controls the operations of the memory, ALU, and the input/output subsystem. Input/Output The input subsystem accepts input data and the program from outside the computer; the output subsystem sends the result of processing to the outside.
- 10. STORED PROGRAM CONCEPT The von Neumann model states that the program must be stored in memory. This is totally different from the architecture of early computers in which only the data were stored in memory. Both the data and programs should have the same format because they are stored in memory. They are, in fact, stored as binary patterns (a sequence of 0s and 1s ) in memory. SEQUENTIAL EXECUTION OF INSTRUCTIONS A program in the von Neumann model is made of a finite number of instructions. In this model, the control unit fetches one instruction from memory, interprets it, and then executes it.
- 11. 1.5 COMPUTER SOFTWARE PROGRAMS MUST BE STORED A SQUENCE OF INSTRUCTIONS Another requirement of the model is that the program must be a sequence of instructions. Each instruction operates on one or more data items.
- 12. ALGORITHMS The step-by-step solution is called an algorithm. LANGUAGES A computer language has a more limited number of symbols and also a limited of words . SOFTWARE ENGINEERING Software engineering is the design and writing of structured programs. Today, it is not acceptable just to write a program that does a task; the program must follow strict principles and rules. OPERATING SYSTEMS An operating system originally worked as a manager to facilitate access of the computer components for a program. Today, operating systems do much more.
- 13. 1.6 HISTORY MECHANICAL MACHINES (BEFORE 1930) BIRTH OF ELECTRONIC COMPUTERS (1930-1950) Early Electronic Computers The early computers of this period did not store the program in memory; all were programmed externally. The first general-purpose, totally electronic computer was made by John Mauchly and J.Presper Ecke r t and was called ENIAC (Electronic Numerical Integrator and Calculator). It was completed in 1946. Computers Based on the von Neumann Model The first computer based on von Neumann’s idea was made in 1950 at the University of Pennsylvania and was called EDVAC (Electronic Discrete V ariable Automatic Computer) .
- 14. COMPUTER GENERATIONS (1950-PRESENT) Computer built after 1950 are following, more or less, the von Neumann model. The computers has become faster, smaller, and cheaper, but the principle is almost the same. Each generation witnesses some major change in hardware or software (but not the model). The first generation is characterized by the emergence of commercial computers. Computers were bulky and used vacuum tubes as electric switches. First Generation (roughly 1950-1959)
- 15. The invention of integrated circuit (transistors, wiring, and other components on a single chip) reduced the cost and size of computers even further. Minicomputers appeared on the market. Software industry was born. Third Generation (roughly 1965 -1975 ) Second-generation computers used transistors instead of vacuum tubes. This reduced the size of computers as well as their cost. Two high-level programming languages, FORTRAN and COBOL , were invented and made programming easier. Second Generation (roughly 1959-1965)
- 16. The fourth generation saw the appearance of microcomputers. Advances in the electronics industry allowed whole computer subsystems to fit on a single circuit board. This generation also saw the emergence of computer networks. Fourth Generation (approximately 1975-1985) The fifth generation witnessed the appearance of laptop and palmtop computers, improvements in secondary storage media (CD-ROM, DVD, etc.), the use of multimedia, and the phenomenon of virtual reality. Fifth Generation (approximately 1985-NOW)
- 17. SUMMARY Computer science, in this text, means issues related to a computer. A computer is a programmable data processor that accepts input data and programs and outputs data. A program is a set of instructions executed sequentially that tells the computer what to do with data. Every computer today is based on the von Neumann model.
- 18. SUMMARY (continued) The von Neumann model specifies a memory subsystem, an arithmetic logic unit subsystem, a control unit subsystem, and an input/output subsystem. Data and programs are stored in computer memory. A step-by-step solution to a problem is called an algorithm. A program is written in a computer language. Software engineering is the design and writing of programs in a structured form.
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