The versatility of a computer is enhanced considerably if it can communicate with other computers or a number of users. The very first computers were large machines that occupied an entire room with a control console at the center. The input and output devices for these machines were located at that console and only one user could operate the machine at a time. However, not long after the first computers were made, engineers realized that it would be more efficient if users could access the machine from their desks via a "terminal." This was the beginning of the "mainframe" computer.

The key to a mainframe computer was a communications network that would allow users to link to the machine. The terminals had no computing power themselves, but were connected to the mainframe computer via copper wire, sometimes called twisted pair. As computers became larger...