Cable

For communications between computers that are linked by cable, there are three choices.

Twisted wire	(phone line) Advantage: Easy to string Cheap Disadvantage: Subject to interference = static and garble
Coaxial cable	(round insulated wire) Advantage: Not susceptible to interference Transmits faster Disadvantage: Heavy & bulky Needs booster over distance
Fiber optic line	(glass fibers) Advantage: Smaller Lighter Faster No interference Disadvantage: Expensive Harder to install and modify

Broadcast

For longer distances or when cables are not practical, other transmission media come into play. We're getting really high tech here!

It may seem odd to call microwaves, radio waves, or light a "physical" medium. All are electromagnetic in nature. Sometimes they are treated by scientists like streams of teeny, tiny particles and other times like waves on the beach. In their "particle" life, they do behave like a bunch of physical particles. So it's not quite as odd as it first appears. (But all those electromagnetic things are plenty odd!)

Wireless	(infrared, light, radio) Advantage: Flexible Portable Disadvantage: Slower data transfer than hard-wired methods Subject to interference
Microwave	Advantage: Speed of light Uses a few sites Disadvantage: Line-of-sight only
Satellite	Advantage: Always in sight Disadvantage: Expensive uplink and downlink facilities