CHAPTER 2 - DIGITAL DATA REPRESENTATION AND NUMBERING SYSTEMS
INTRODUCTION • Digital computers use sequences of binary digits (bits) to represent numbers, letters, special symbols, music, pictures, and videos. For this reason, we study the Digital Data Representation and Numbering System in order to understand how computers store information in Binary digits
TYPES OF SIGNAL - ANALOGUE SIGNAL • An analog or analogue signal is any variable signal continuous in both time and amplitude. • Analog signals are represented as sine wave. The sine wave's amplitude value can be seen as the higher and lower points of the wave, while the frequency (time) value is measured in the sine wave's physical length from left to right.
TYPES OF SIGNAL - ANALOGUE SIGNAL Examples of analog signals: A good example of an analogue signal is the loud- speaker of a stereo system. When the volume is turned up, the sound increases slowly and constantly. The sound from a human voice is analog, because sound waves are continuous, Even a typical kitchen clock having its hands moving continuously can be represented as an analog signal
TYPES OF SIGNAL - DIGITAL SIGNAL Digital Signal is discrete signal in both time and amplitude. A digital signal refers to an electrical signal that is converted into a pattern of bits. These patterns can be generated in many ways, each producing a specific code. digital signals can take only a limited number of values (discrete steps); usually just two values are used: the positive supply voltage (+Vs) and zero volts (0V).
TYPES OF SIGNAL - DIGITAL SIGNAL Logical States +Vs 0Vs True False On Off High Low 1 0
ANALOGUE TO DIGITAL CONVERTOR (ADC) If you want to attach an analogue input device to a digital device such as a computer, you will need an analogue to digital convertor(ADC). A good example of a computer peripheral that requires an ADC is a microphone. When you plug a microphone into a computer, you are actually plugging it into an ADC which converts the analogue signals from the microphone into digital data that the computer can then process.
Digital to Analogue Convertor (DAC) • If you want to attach an analogue output device to a digi tal device such as a computer, you will need a digital to analogue convertor(DAC). • A good example of a computer peripheral that requires a DAC is a loud speaker or headphones. • When you plug a loudspeaker into a computer , you are actually plugging it into a DAC, which takes digital data from the computer and converts it into analogu e signals which the loudspeaker then converts into sound.
Digital to Analogue Convertor (DAC) • Another device that contains a DAC is an MP3 player. The music data stored in the player is all digital, but the player produces analogue signals which the headphones convert into sound. Note: • The ADC and DAC in a computer that are used for connecting microphones and loud speakers are part of the computer’s sound card.
Data Representation-Text/Character Data Representation • Any piece of data that is stored in a computer’s memory must be stored as a binary number. Data is not just alphabetic characters, but also numeric characters, punctuation, spaces, etc. • When a character is stored in memory, it is first converted to a numeric code. The numeric code is then stored in memory as a binary number • Historically, the most important of these coding schemes is ASCII, which stands for the American Standard Code for Information Interchange . It is the most commonly used coding technique for alphanumeric data.
Data Representation-Text/Character Data Representation • Old version of ASCII characters are represented in 7 bits. So 2 7 =128 numeric codes, those represent the English letters, various punctuation marks, and other characters. Extended version of ASCII characters are represented in 8 bits. So 2 8 =256 numeric codes are used for alphanumeric characters. • ASCII value for ‘A’ is 65; ‘B’ is 66 and so on. ASCII value for ‘a’ is 97 and ‘b’ is 98 and so on. ASCII value for 0 is 48, 1 is 49 and so on • ASCII is limited however, because it defines codes for only 128 or 256 characters. To remedy this, the Unicode character set was developed in the early 1990s.
Data Representation-Text/Character Data Representation • Unicode (Universal Code) is an extensive encoding scheme that is compatible with ASCII, but can also represent characters for many of the natural languages in the world. The Unicode character set uses 16 bits per character. • Therefore, the Unicode character set can represent 2 16 =65,536 characters. Unicode was designed to be a superset of ASCII. That is, the first 256 characters in the Unicode character set correspond exactly to the extended ASCII character set. • Today, Unicode is quickly becoming the standard character set used in the computer industry
Data Representation-Images and Graphics • Digitizing a picture is the act of representing it as a collection of individual dots called pixels ( Picture elements ). Each pixel is assigned a tonal value (black, white, shades of gray or color), which is represented in binary code (zeros and ones). • The number of pixels used to represent a picture is called the resolution . Resolution is usually expressed by numbers for horizontal and vertical: 640 by 480 means 640 pixels wide, by 480 pixels tall. • The storage of image information on a pixel-by-pixel basis is called a raster-graphics format . Most popular raster file formats are: JPEG, GIF, BMP, TIFF, PCX and PNG.
Data Representation-Images and Graphics • Color is our perception of the various frequencies of light that reach the retinas of our eyes. • Color is often expressed in a computer as an RGB (red-green-blue) value, which is actually three numbers that indicate the relative contribution of each of these three primary colors. • For example, an RGB value of (255, 255, 0) maximizes the contribution of red and green, and minimizes the contribution of blue, which results in a bright yellow.
Data Representation-Sound/Audio • Sound is perceived when a series of air compressions vibrate a membrane in our ear, which sends signals to our brain. • Several popular formats are: WAV, AU, AIFF, VQF, and MP3. Currently, the dominant format for compressing audio data is MP3
Data Representation - Video/Animation • What is video? – is the technology of electronically capturing, recording, processing, storing, transmitting and reconstruction a sequence of still images representing scenes in motion – It is a collection of still images • Common video codec’s formats are: AVI, MOV, MPEG (Moving Pictures Expert Group) and MP4
NUMBERING SYSTEM • A number system is the set of symbols used to express quantities as the basis for counting, determining order, comparing amounts, performing calculations, and representing value. Examples of numbering systems are decimal, binary, hexadecimal and octal numbering system. • In order to represent numbers of different bases, we surround a number in parenthesis and then place a subscript with the base of the number. • A decimal number is written (9233) 10 • A binary number is written (11011) 2 • An octal number is written (7133) 8 • A hexadecimal number is written (2BC1) 16 g system
DECIMAL NUMBER SYSTEM • The decimal number system is used in our everyday life. It has values from 0 – 9. Decimal number system has a base of 10. • This means that each digit in the number is multiplied by 10 raised to a power corresponding to that digit’s position. (4928) 10 8 x 10 0 = 8x1 2 x 10 1 = 1x10 9 x 10 2 = 9x100 4 x 10 3 = 4x100
Binary Number System • Binary is a number system used by digital devices like computers. In the binary system, there are only two digits, 0 and 1. The binary system is said to have a base of 2. (1001) 2 1 x 2 0 = 1x1 0 x 2 1 = 0x2 0 x 2 2 = 0x4 1 x 2 3 = 1x 8
Octal Number System • Octal number system is a numeral system with a base of 8. The values are represented by 0-7. Each octal digit represents three (3) binary bits.
Hexadecimal Number System • Hexadecimal number system is a numeral system with a base of 16. The values are represented by 0-9, A,B,C,D,E,F. Each hexadecimal digit represents four (4) binary bits
Numbers with Different Base Decimal Numbers Binary Numbers Octal Numbers Hexadecimal Numbers (Base 10) ( Base 2) (Base 8) (Base 16) 0 0000 00 0 1 0001 01 1 2 0010 02 2 3 0011 03 3 4 0100 04 4 5 0101 05 5 6 0110 06 6 7 0111 07 7 8 1000 10 8 9 1001 11 9 10 1010 12 A 11 1011 13 B 12 1100 14 C 13 1101 15 D 14 1110 16 E 15 1111 17 F
Why we study binary number system? • Most computers use the simple type of digital technology. Their electronic circuits have only two possible states “on” and “off”. When discussing these states, we usually indicate the “on” state with 1 and the “off” state with 0. These 1’s and 0’s are referred to as “bits” which is an abbreviation to “ b inary dig its ”. • The above picture represents 01001101. • When data is input into a computer, the numbers or words we understand are translated into a binary numbers system. Binary is the language of computers .
Recommend
More recommend
