byte1                    byte2                    byte3                     byte4

              |<---------------->|<---------------->|<---------------->|<---------------->|

Class A     |0  Net ID            |                             Host ID                                 |

Class B     |10                      Net ID              |                        Host ID              |

Class C     |110                                            Net ID               |       Host ID      |

Class D     |1110                                      Multicast Address                             |

Class E      |1111                                     Reserved for future use                    |

Now Class A addresses are numberically the lowest they use 1 byte to identify class type and net id.

Now number of net ids possible in class A are : 2^7 and number of hosts possible are 2^24

Similarily number of net ids possible in class B are : 2^14 and number of hosts possible are : 2^16

Number of net ids possible in class C are : 2^21 and number of hosts possible are:2^8

We can represent these addresses as string of 1 and  0 like:

10000000 00001011 00000011 00011111

or we have dotted decimal notation to represent the same address in decimal numbers, with

each byte being separated by a '.' i.e.:

128.11.3.31

Class Ranges of Internet addresses

                              From                                            To

Class A                  0.0.0.0                                127.255.255.255

Class B               128.0.0.0                                191.255.255.255

Class C               192.0.0.0                                223.255.255.255

Class D               224.0.0.0                                239.255.255.255

Class E               240.0.0.0                                240.255.255.255