VIEWS: 19 PAGES: 20 CATEGORY: Computers & Internet POSTED ON: 2/24/2011 Public Domain
Катедра Информационни технологии и комуникации Informatics (The Science of Information Systems) Lecture 1 – Introduction 2011 Textbook J.Glenn Brookshear, Computer Science, An Overview, 10th edition, Addison Wesley / Pearson eddition, 2007 2 Scope of the Course The course has the aim to explain: •What is data and how it is presented in computers •What are algorithms, computer programs, Programming languages •What are the Computer architectures •How to store data and what is Data base management system (DBMS) •How to exchange data between computers •What is Operating system •What is application software •Which are the most used computer technologies •What is Information system •What is Internet and its generations •What is Information security •How to design Information systems •What are the eBusiness applications •Project management •How to make Blogs and Websites 3 Received practical knowledge and experience During the Labs the students will receive knowledge and experience for design and using Information systems dedicated to Corporated and Public sector organisations Each student will be able to design small information system, using the available in the PC Office products The work will be in team by 2 The information systems will be build using the two Microsoft products oMS Excel oMS Access There will be Course works for each team There will be 2 tests The exam will be via test The final marks will be as a result of the Exam, Tests and the Course work Every student has to create its own Blog and its own WebSite – compulsory 4 Origin of Computers Initial ideas – from Greek and Roman civilization – Abacus - for addition Some beginner ideas oBlaise Pascal (1623-1662) – a machine for addition using gear with zero positioning oCharles Babbadge (1792-1871) – a machine for addition, with printing on paper; with the other arithmetic operations; punching of commands for execution Idea for algorithm – sequence of holes on paper oJoseph Jacquard (1752-1834) – developed a weaving loom with weaving o process determined by holes in paper cards Idea for representing data – via holes on paper oHermann Hollerith (1860-1929) oHis work was the base for establishment of IBM Co Using electricity and electronics in 1900’s 1940 – Bell Laboratories – Mark I –electronically controlled mechanical relays 1937-1941 John Atanasoff-Berry – first computer on electronic tubes - в Iowa State College Mainframes (1950-60) Mini computers (1960-70) Personal computers (1970-80) 5 The science of Algorithms Extending the computer capabilities of execution sequence of commands leaded to evolution of algorithms Gödel incompleteness theorems have created the conditions to have few command sequences performing the same results – options for solutions / options for algorithms In the world 2 sciences have been established : oComputer Science – a science for algorithms oInformation Systems – a science for creation computer systems Working with algorithms, there are few questions: oWhich problems can be presented via algorithms oWhich problems is reasonable to solve via algorithms run on computers oHow easy is to create (discover) an algorithms oHow to analyse and evaluate algorithms oHow to treat data oHow to provide intelligent computer behavior using algorithms oWhat is the influence on the societies using algorithms 6 Information systems •The Information system is a complex of hardware and software elements, linked into an integrated system, providing data treatment of an organisation •Information system has an aim to support the execution of the business in the organisation, involving people, documents, data processing technologies, procedures for running the system •To support the entire business, the Information systems use many different Information and Communication Technologies (ICT) •There are information systems supporting only a part of the corporate business, called Sub-systems of the Information system, e.g. Accounting system, Stock control system, HR system, CAD systems, etc. 7 Base system for presenting numbers Each system consisting of symbols and rules for their use, for presenting any number. In base 10, the symbols are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. The symbols are digits; Position in the number can be or not important Non-positional system(Rome) – VII, и positional (decimal ) systems - 71 Conversion of numbers from one base to another base •Example for conversion the decimal number 121 into base 2 (using only the digits 0 and 1) 121:2=60 remainder 1 60:2=30 remainder 0 30:2=15 remainder 0 15:2=7 remainder 1 7:2=3 remainder 1 3:2=1 remainder 1 1<2 final remainder 1 The result is 1111001 in base 2 •Example of conversion of decimal number 201 into base 16 (using the digits 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F) 201:16=12 remainder 9 (9) 12<16 final remainder 12 (C) The result is C9 in base 16 8 Binary arithmetic (1 of 2) •Using the digits 0 and 1 •Addition 0+0 = 0 10110 0+1 = 1 + 11011 1+0 = 1 ------------------- 1+1 = 10 110001 1+1+1=11 •Subtraction 0-0 = 0 11000101 1-0 = 1 - 1101100 1-1 = 0 -------------------- 10-1 = 1 1011001 •Multiplication 0х0 = 0 11001 0x1 = 0 x 1101 1x0 = 0 ------------- 1x1 = 1 11001 00000 11001 11001 ============= 9 101000101 Binary arithmetic (2 of 2) •Division – using multiplication and subtraction •Example – to divide 10000,111 on 10,1 10000,111:10,1 = 1 0 0 0 0 1,1 1 : 1 0 1 = 1 1 0,1 1 - 101 ------- 110 - 101 --------- 11 (cannot be subtracted with positive result) - 101 -------- 111 - 101 ---------- 101 - 101 ----------- 000 10 Grouping of binary data in computers •Minimal unit – 1 bit •Unit for operation – 1 byte = 8 bits •There are binary operations, but there are not used too often •Word – 4 bytes •Double word – 8 bytes •A character is presented via: oSingle byte – most often used code tables o2 bytes – for covering all languages, including Chinese and Japanese •There a few internationally standardised Coding tables for correspondence between a symbol and its binary representation: oASCII – main symbols are coded in 7 bit combinations, while the other alphabets (Cyrillic, Scandinavian, some French /German characters) is used the 8th bit for coding. This Coding table is used in PC, Unix servers, MS. The table has 94 printable characters oEBCDIC – use all 8 bits for coding. Applied for Mainframes oUnicode – uses 2 bytes for represent a symbol – for coding more than 100,000 symbols 11 Number representation in computers •The numbers are presented in computers as •Fixed point numbers •Floating point numbers •Binary-decimal numbers •Fixed point numbers are integer, with fixed position of the point (binary point) sign Value of the number •Floating point numbers have mantissa, exponent and sign sign exponent mantissa (+) (27) (397485) •Binary-decimal numbers use 4 bits for each decimal digit representation. The number is presented via sequence of such 4 bit constructions 1 0 0 1 0 1 1 1 0 0 1 0 0 1 0 1 => 9725 9 7 2 5 12 Fixed point numbers •They are integer •The negative numbers are presented in 2’ Complement code Positive number Negative number 0 000 0000 0000 1010 => (+10) 1 111 1111 1111 0110 =>(-6) •Using 2’ Complement code, the operation Subtraction is converted to Addition А-B = A + (-B) -> A + (B)2’Compl •There are 2 systems for presenting Fixed point numbers, depending where is MSB (the Most Significant Bit) •MSB is on left знак стойност на числото •MSB is on right знак стойност на числото •The length is 4 bytes / 8 bytes. In 4 bytes the possible numbers amount is +- 2 billion 13 Floating point numbers •Floating point numbers have advantages to Fixed point numbers, that they can present any non-integer number •The mantissa is treated as number based on 16. For this reason the exponent works on base 16 as well •The sign represent the sign of the mantissa. There is no place for the sign of the exponent. The exponent uses 7 bits. The exponent in the Floating point representation is always positive and it is for 0 to 127. This is a machine meaning exponent and it corresponds to the real exponents from -64 to +63. •The length is 8 bytes or 16 bytes, where only the mantissa varies. •The Floating point numbers are not only used in scientific calculations; they are used always where numbers can be non-integer. 14 Logical (Boolean) operations •In computers the information is presented in binary form •The variables can have values 0 or 1. There is a special algebra, created by Boole, working with truth vales. This algebra is applied in computers and it is called “Boolean algebra” or “Logical operations”. •The Boolean function can have 2 options as value – truth or false, presented in the computers as 1 or 0. •Boolean functions are defined most often in tables X value Y value X&Y vale 0 0 0 0 1 0 1 0 0 1 1 1 15 Main Boolean functions and their realisation in computers •Logical AND •Logical Exclusive OR X Y X&Y X Y X^Y 0 0 1 0 0 0 0 1 0 0 1 0 1 0 0 1 0 0 1 1 0 1 1 1 X (1) (1) X X & Y (0) X^Y (0) Y (0) Y (0) •Logical OR •Negative X Y X|Y X -X 0 0 0 0 1 0 1 1 1 0 1 0 1 1 1 1 X (1) X (1) -X (0) X|Y (1) Y (0) 16 Components for building Computers (1 of 4) •Trigger – component for storing information of a Boolean variable R Q Reset Input Output Q S Set Input R Q Тr S 17 Components for building Computers (2 of 4) •Register – component for storing an information word – Byte, Word, Double word, etc. Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Q Q Q Q Q Q Q Q Тr Тr Тr Тr Тr Тr Тr Тr R R R R R R R R S S S S S S S S S7 S6 S5 S4 S3 S2 S1 S0 18 Components for building Computers (3 of 4) •Adder (Summer) – executes operation Addition of 2 numbers •Adder is the main component for doing Addition, Subtraction (via 2’s Complement code), Multiplication and Division •Addition is made by n equal action of Adders Si Xi Yi Ci-1 Si Ci 0 0 0 0 0 0 0 1 1 0 ∑ 0 1 0 1 0 0 1 1 0 1 Ci Ci-1 1 0 0 1 0 Xi Yi 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1 S3 S2 S1 S0 ∑ ∑ ∑ ∑ C3 C2 C1 C0 InC X3 Y3 X2 Y2 X1 Y1 X0 Y0 19 Components for building Computers (4 of 4) •Logical circuit of Adder Ci Si . . . . .. . . . . . . Xi . . Yi Ci-1 20