Computer Basics

Encoding Schemes
&
Number System

Encoding is converting characters (letters, numbers etc) to special format
The following are the different encoding schemes
   • ASCII (American Standard code for Information Interchange)
   • Unicode
         UTF-8
         UTF-16
         UTF-32
   • ISCII (Indian Script code for Information Interchange)

ASCII (American Standard code for Information Interchange)
  • Ascii uses 7-bit code to represent character
  • Ascii has 128 characters numbered 0 to 127
  • If Ascii uses the 8-bit code (the first being the most significant bit) it has 256 characters. This is called Extended Ascii
  • Ascii can set the most significant bit as 0 or as parity bit)
  • Ascii do not support different languages

Unicode
  • It is universal character set
  • Covers the characters of all languages
  • It uses 8 bit (utf-8), 16 bit (utf-16), and 32 bit (utf-32) encoding
  • It occupies more space

ISCII (Indian Script Code for Information Interchange)
  • It is an 8-bit code that represents Indian languages
  • 0 to 127 are Ascii codes and 128 to 255 are characters of Indian languages
  • The character set is simple
  • Lot of Indian languages are covered by this
  • A special keyboard is required to use this
  • Unicode includes ISCII characters.

Number System
  • It is a method to write numbers
  • The number of unique characters in a number system is called the base of the number system or the radix. E.g. In binary system there are 2 unique characters 0 and 1
  • It is also called positional number system because the value of each number depends on its position

Types of Number System
  • Decimal number system
  • Binary number system
  • Octal number system
  • Hexadecimal number system

Decimal number system
  • Numbers 0 to 9 are used
  • It is called base-10 system
  • Number has positional value also
  • Example: 128.53 = 1*(10)2 + 2*(10)1 + 8*(10)0 + 5*(10)-1 + 3*(10)-2
Binary Number System
  • Computers use binary number system
  • It has 2 digits 0 and 1
  • It is called base-2 system
  • Example: Decimal number 4 is binary 00000100 (1*22)

Octal number system
  • Numbers 0 to 7 are used
  • It is called base-8 system
  • Convert 256 octal to decimal
      (2*82)+(5*81)+(6*80) = 174

Hexadecimal number system
  • Numbers 0 to 9 and alphabets A to F
  • It is called base-16 system
  • Convert 2B3 hex to decimal
      (2*162) + (11*161) + (3*160) = 691

Summary: Encoding is converting characters to special format. The different encoding schemes are ASCII (American Standard code for Information Interchange), Unicode and ISCII (Indian Script Code for Information Interchange). The method to write numbers is called Number System. The different number systems are Decimal number system, Binary number system, Octal number system and the hexadecimal number system. Computers use the binary number system and humans generally use the decimal number system.