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Introduction to Computer Science. Dr. Nagy Ramadan. E-mail: Nagyrdo@yahoo.com. Lecture - 2. Outline. Part 1 - Categories of Modern Computers Part 2 - Types of Microcomputer Machines Part 3 - Data Representation in Modern Computers Part 4 - Numbering Systems.

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## Introduction to Computer Science

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**Introduction to Computer Science**Dr. Nagy Ramadan E-mail: Nagyrdo@yahoo.com Lecture - 2**Outline**• Part 1 - Categories of Modern Computers • Part 2 - Types of Microcomputer Machines • Part 3 - Data Representation in Modern Computers • Part 4 - Numbering Systems**Categories of Modern Computers**• Technology • Analog computers • Digital computers • Hybrid Computers • Usage • Special-purpose computers • General-purpose computers • Size and computational capabilities • Super computers • Mainframes computers • Minicomputers • Microcomputers**Types of Microcomputer Machines**• Personal computers • Desktop (or tower) • Notebook (or laptop) • Tablet (touch-sensitive screen, used as a writing or drawing pad ) • Handheld computer Ex: PocketPC. It is Called “Personal Digital Assistant” (PDA). • Workstations • Servers • Videogames consoles**Data Representation in Modern Computers**• Main memory can only store data in the form of 0 and 1, therefore, digital computers can only deal with information represented as binary values (0,1). • All information entered to the digital computers should be represented as a sequence of binary digits. Binary digit is usually abbreviated as: bit. • Bit is quite little piece of information to be handled in digital computer’s main memory during the execution of an algorithm. Therefore, for practical reasons, main memory is usually divided into large number of cells (called words), with typical cell sizes being: 8, 16, or 32 bits. byte=8 bits**Numbering Systems**Positional numbering systems are efficient for representing any real numbers. The decimal numbering system is considered the most famous and widely accepted numbering system to humanity for many centuries. To define a positional numbering system, it is needed to determine its base (also called radix), and its list of adopted symbols.**The Decimal Equivalent Value**In general, the decimal equivalent value for any real number of a positional numbering system with base R is: Where digits to the left of the R-point is considered integer part, where digits to the left of the R-point is considered the fractional part.**Example (1) - Decimal System Value:**The number 724.53 is calculated in the decimal system as follows: EX: ( 7 2 4 . 5 3 )10 positions 2 1 0 . -1 -2 (724.53)10 = 7*102 + 2*101 + 4*100 + 5*10-1 + 3*10-2 = 700 + 20 + 4 + 0.5 + 0.03**Example (2) - (Binary System):**The equivalent decimal value of the binary number 1011 is: (1011)2 = 1*23 + 0*22 + 1*21 + 1*20 = 8 + 0 + 2 + 1 = (11)10**Example (3) - (Binary System):**The equivalent decimal value of the binary number 11011.101is: (11011.101)2 = 1*24 + 1*23 + 0*22 + 1*21 + 1*20 + 1*2-1 + 0*2-2 + 1*2-3 = 16 + 8 + 0 + 2 + 1 + .5 + 0 + .125 = (27.625)10**Example (4) - (Ternary System):**The equivalent decimal value of the ternary number 201.2is: (201.2)3 = 2*32 + 0*31 + 1*30 + 2*3-1 = 18 + 0 + 1 + .666 = (19.666)10**Example (5) - (Octal System):**The equivalent decimal value of the octal number 127.64is: (127.64)8 = 1*82 + 2*81 + 7*80 + 6*8-1 + 4*8-2 = 64 + 16 + 7 + .75 + .0625 = (87.8125)10**Example (6) - (Hexadecimal System):**The equivalent decimal value of the hexadecimal number 1CF.A3is: (1CF.A3)16 = 1*162 + C*161 + F*160 + A*16-1 + 3*16-2 = 1*162 + 12*161 + 15*160 + 10*16-1 + 3*16-2 = 256 + 192 + 15 + .625 + .01171875 = (463.63671875)10

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