Physical media

Physical media refers to the physical materials that are used to transmit information in data communications. It is referred to as physical media because the media is generally a physical object such as copper or glass. It can be touched and felt, and has physical properties such as weight and color. For a number of years, copper and glass were the only media used in computer networking.

Copper wire is currently the most commonly used type of physical media due to the abundance of copper in the world, as well as its ability to conduct power. Copper is also one of the cheaper metals which makes it more feasible to use.

Most copper wires used in data communications today have eight strands of copper, organized in unshielded twisted pairs, or UTP. The wires are twisted around one another because it reduces electrical interference from outside sources. In addition to UTP, some wires use shielded twisted pairs (STP), which reduce electrical interference even further. The way copper wires are twisted around one another also has an effect on data rates. Category 3 cable (Cat3), has three to four twists per foot and can support speeds of 10 Mbit/s.Category 5 cable (Cat5) is newer and has three to four twists per inch, which results in a maximum data rate of 100 Mbit/s. In addition, there are category 5e (Cat5e) cables which can support speeds of up to 1,000 Mbit/s, and more recently, category 6 cables (Cat6), which support data rates of up to 10,000 Mbit/s (or 10 Gbit/s).

On average, copper wire costs around $1/foot.

Optical fiber is a thin and flexible piece of fiber made of glass or plastic. Unlike copper wire, optical fiber is typically used for long-distance data communications, being that it allows for data transmission over far distances and can produce high transmission speeds. Optical fiber also does not require signal repeaters, which ends up reducing maintenance costs, since signal repeaters are known to fail often.

There are two major types of optical fiber in use today. Multimode fiber is approximately 62.5 µm in diameter and utilizes LEDs to carry signals over a maximum distance of about 2 kilometers. Single mode fiber is approximately 10 µm in diameter and is capable of carrying signals over tens of miles.

...
Wikipedia