Islamic University Of Gaza, Nael Aburas Data Storage Introduction to computer, 2nd semester, 2010/2011 Mr.Nael Aburas Faculty of Information Technology Islamic University of Gaza Islamic University Of Gaza, Nael Aburas1

Outline Introduction Bits and their storage Boolean operations Gates Main memory Memory organization Mass storage Islamic University Of Gaza, Nael Aburas2

Introduction We begin our study of computer science by considering how information is encoding and stored inside computers Islamic University Of Gaza, Nael Aburas3

Bits and their storage Inside the computers information is encoded as patterns of 0s and 1s. These digits are called bits (binary digits). bits are used to represent: ◦ Numeric values ◦ Characters ◦ Images ◦ Sounds Islamic University Of Gaza, Nael Aburas4

Boolean operations bit 0 represent the value false bit 1 represent the value true Operations that manipulate true/false values are called Boolean operations. basic Boolean operations are: ◦ AND, OR, and XOR (exclusive or) There is also NOT Islamic University Of Gaza, Nael Aburas5

Boolean operations AND, OR, and XOR operators take two operands, but the NOT operator takes a single operand ◦ AND  The AND operator performs logical conjunction on two Boolean expressions.  If both expressions are equal to true (1), then the AND return true, otherwise all other cases should produce an output False (0) Input1Input2output Truth table Islamic University Of Gaza, Nael Aburas6

Boolean operations OR The OR operator performs logical disjunction on two Boolean expressions. OR operator returns true value when at least one of their Boolean expression is equal to true. Input1Input2output Truth table Islamic University Of Gaza, Nael Aburas7

Boolean operations XOR (exclusive or) XOR performs logical exclusion on two expressions. XOR produce an output of 1 (true) when one of its inputs is 1 and the other is 0 (In short, the XOR operation produces an output of 1 when its input are different) Input1Input2output Truth table Islamic University Of Gaza, Nael Aburas8

Boolean operations NOT The operation NOT is another Boolean operation. It differs from AND, OR, and XOR because it has only one input. Its output is the opposite of that input. InputOutput Truth table Islamic University Of Gaza, Nael Aburas9

Gates and Flip-flops Gate is a device that produces the output of a Boolean operation. Its often implemented as (small) electronic circuits, in which the digits 0 and 1 are represented as voltage levels. Gates provides the building blocks from which computer are constructed. Islamic University Of Gaza, Nael Aburas10

Islamic University Of Gaza, Nael Aburas Gates 11

Islamic University Of Gaza, Nael Aburas Exercise What input bit patterns will cause the following circuits to produce an output of 1? Islamic University Of Gaza, Nael Aburas12