The UNIX operating system is made up of three parts; the kernel, the shell and the programs. The kernel of UNIX is the(71)of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to(72). The shell acts as an(73)between the user and the kernel. When a user logs in, the(74)program checks the username and password, and then starts another program called the shell. The shell is a command line(75)(CLI). It interprets the commands the user types in and arranges for them to be carded out. The commands are themselves programs: when they terminate, the shell gives the user another prompt(% on our systems).