1. Islamic University Of Gaza, Nael Aburas Data Storage Introduction to computer, 2nd semester, 2010/2011 Mr.Nael Aburas nras@iugaza.edu.psnras@iugaza.edu.ps Faculty of Information Technology Islamic University of Gaza Islamic University Of Gaza, Nael Aburas1

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

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

4. 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

5. 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

6. 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 000 010 100 111 Truth table Islamic University Of Gaza, Nael Aburas6

7. 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 000 011 101 111 Truth table Islamic University Of Gaza, Nael Aburas7

8. 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 000 011 101 110 Truth table Islamic University Of Gaza, Nael Aburas8

9. 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 01 10 Truth table Islamic University Of Gaza, Nael Aburas9

10. 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

11. Islamic University Of Gaza, Nael Aburas Gates 11

12. 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