DATA REPRESENTATION CHAPTER 2

2.1 DATA TYPES

Different types of data (Fig. 2.1) The computer industry uses the term “MULTIMEDIA” to define information that contains numbers, text, images, audio and video.

If there’re different types of data.. Do we’ve different types of computers for each data type So.. Ex. Is there a computer to process only numbers The Answer is: NO

2.2 DATA INSIDE THE COMPUTER

DATA Text Images Videos Audio COMPUTER Bit The smallest unit of data that can be stored in a computer. it is either 0 or 1 1 = ON 0 = OFF

BIT PATTERN All data types are transformed into a uniform representation when they are stored in a computer and transformed back to their original form when retrieved. This universal representation is called a bit pattern A Bit pattern made of 16 bits

How does a computer memory know what type of data a stored bit pattern represents The Answer is: It Doesn’t It’s the responsibility of input/output devices or programs

Data Coding & Decoding

BYTE Bit Pattern of length 8 = BYTE Bytes used to measure the size of memory or other storage.

2.3 REPRESENTING DATA

Represent each symbol with bit pattern TEXT

How many bit patterns we need to represent the ENGLISH letters The Answer is: 52 bit patterns 26- Uppercase Letters 26- Lowercase Letters

TEXT If we’ve an Imaginary language that uses ONLY 4 symbols. What is the bit pattern length we need to represent this language The Answer is: bit pattern of length 2

TEXT Bit pattern length# of Symbols ,536

TEXT Different sets of bit patterns have been designed to represent text symbols Each set is called a CODE

ASCII: The American standard code for information interchange. use 7 bit for each symbol Extended ASCII To make the size of each pattern 1 byte ( 8 bits) EBCDIC : Extended binary coded decimal interchange code. Only IBM main frames. Uses 8 bits pattern Unicode uses 16 bits. To represent more symbols for other languages not just English ISO International Organization for Standardization Has designed a code using 32bit pattern Examples of CODES

Representing of the word “BYTE” in ASCII code

Numbers are representing using the binary system before being stored in the computer memory. as described in Chapter 3. NUMBERS

Image representation methods Vector Bitmap IMAGES Image divided into a matrix of PIXELS ( picture elements ) where each pixel is small dot An image is decomposed into a combination of CURVES and LINES.

Bitmap IMAGES Example of representing a black & white image using bitmap method

Bitmap IMAGES Representation of color pixels using bitmap method (8 bit pattern) BGR RED  GREEN  BLUE  WHITE 

Vector IMAGES An image is decomposed into a combination of curves and lines. Each line or curve represented by a mathematical formula. Ex. Representing a LINE by the coordinates of it’s end points

IMAGES Which one is better.. Bitmap method OR Vector method

VIDEOS Is a representation of images (called FRAMES) in time. A Movie is a series of frames shown one after another to create the illusion of motion

If you want to manipulate bit patterns. Is it easy for you to write & remember a long stream of 0's &1's The Answer is: NO That’s why we use Hexadecimal OR Octal notations

2.4 HEXADECIMAL NOTATION

HEXADEC = 16 IN Greek So.. There are 16 symbols: HEXADECIMAL NOTATION FEDCBA A 4- bit pattern can be represented by a hexadecimal digit, and vice versa.

Hexadecimal digit Bit Pattern A1010 B1011 C1100 D1101 E1110 F1111 Hexadecimal digits HEXADECIMAL NOTATION Hexadecimal digit Bit Pattern

HEXADECIMAL NOTATION FCE = xFCE4 “x” to show that the representation is in Hexadecimal

Example1: Show the hexadecimal equivalent of the bit pattern HEXADECIMAL NOTATION

Example2: What is the bit pattern for x24C? HEXADECIMAL NOTATION

2.5 OCTAL NOTATION

OCT= 8 IN Greek So.. There are 8 symbols: OCTAL NOTATION A 3- bit pattern can be represented by an OCTAL digit, and vice versa.

OCTAL digits OCTAL NOTATION Hexadecimal digit Bit Pattern

OCTAL NOTATION “o” & “0” to show that the representation is in Octal 74 o =

Example1: Show the octal equivalent of the bit pattern OCTAL NOTATION

Example2: What is the bit pattern for 24 8 ? OCTAL NOTATION