Differentiate between Ethernet Fast Ethernet Gigabit Ethernet and 10 Gigabit Ethernet?

Gigabit = 1,000,000,000 bps (bits per second) = 125,000,000 Bps (Bytes per second) = 125 MBps (Megabytes per second (10^3)) = 119.209... MiBps (Mebibytes per second (2^10))10 Gigabit = 10,000,000,000...

The 'Ether' part of Ethernet denotes that the system is not meant to be restricted for use on only one medium type, copper cables, fibre cables and even radio waves can be used. Fast Ethernet Network...

If you want greater speed, why not use gigabit ethernet? Just remember that all the devices and cabling must be capable of that speed or you won't actually see that speed.

Fast Ethernet runs at 100Mbit and requires CAT5e cables. Gigabit Ethernet is 1,000Mbit and requires CAT6 cables

You would use gigabit ethernet in a LAN where you want speed; otherwise, most LANs run at 100 megabits per second, which is considerably slower.