A command line is a line on the screen on which you type commands (instructions) to your computer. It is usually identified by a symbol such as ``%'' or ``$'', called a prompt:
$ type command here
An operating system is a group of programs that provide basic functionality on a computer. These programs operate your computer hardware in response to commands such as copy, sort, and print. An operating system can be seen as a set of functional building blocks upon which other programs depend. It also manages computer resources and resolves resource conflicts, as when two programs want to use a disk drive at the same time.
The Desktop graphical environment is constructed on top of the UNIX operating system. The UNIX system is used on a variety of hardware, ranging from personal computers to supercomputers. It is characterized by its assortment of basic tools (or utilities) and by its ability to support multiple users running multiple programs at the same time.
Another commonly used operating system is DOS, which was designed to support a single user running one program at a time on a single personal computer. Microsoft Windows is a graphical environment built on top of DOS. SCO systems can run most DOS and Windows programs by translating the DOS commands into equivalent UNIX commands. You can use either UNIX or DOS commands from the UNIX command lines, and you can read files from either DOS or UNIX disks.
A network is a group of interconnected computers. Each computer on the network acts independently, but can transfer information to and from other computers on the network.
A local-area network
connects computers at one site directly by a high-speed cable,
usually an Ethernet cable.
A wide-area network (WAN), which can be worldwide,
connects computers at different sites
by transmitting data over telephone lines.