It's fast and inexpensive. There is also of course Fibre-Optics, but the price of the required hardware trumps their usefulness, since most LAN's don't need the amount of speed Fibre Optics offer.
Ethernet
Ethernet cabling is cheap and fast enough for most purposes.
The "star" topology is the most common.
to allow for transmission on two separate LANs at the same time. Perhaps the most common application of dual Ethernet is in firewall machines.
1000Base-LX
BNC
BNC connecter
Cat-5, rj-45.
Cat-5, rj-45.
Cat-5, rj-45.
The most popular is the TCP/IP suite of protocols
Yes, they do. Some people use older computers that need it installed though.