SECTION 1

INTRODUCTION

THE MULTICS SYSTEM

A large-scale computer is a machine that can store very large amounts of information, and can process that information very quickly. A computer consists of hardware, all the physical devices and electronic circuitry, and software, all the programs and other machine instructions that control the activities of the computer. The software is said to "run" or "execute" on the hardware.

In order for people to use a computer, there must be a set of programs within it that can interpret users' instructions, control the hardware, and otherwise supervise the basic operation of the computer. This portion of the software is called the operating system.

Your operating system is called Multics. It is a general-purpose system developed to serve large and diverse user communities. Because Multics is a timesharing system, the work of many users is processed almost simultaneously. The normal mode of operation on Multics is interactive, or "conversational": each instruction that you type goes directly to the computer and is acted on immediately; if Multics needs any further information from you in order to follow your instruction, you are asked for it. In addition, all of your work can be seen and used by other users through a system of access control levels of permission controlled by you.

You will do your work on Multics from a terminal; in fact, this may be the only piece of hardware you see. A terminal looks very much like an electric typewriter (or a television screen) with extra keys. It is connected to the computer, either directly or through normal telephone lines. Although there are many different kinds of terminals, each with slightly different keyboards and instructions for use, all terminals can be classed as either printing terminals (also called "hard-copy" terminals because they print onto paper) or video terminals (with a screen and cathode ray tube, CRT, rather than paper).

MANUAL CONVENTIONS

A few conventions and special symbols should be introduced before you begin to explore the Multics environment.

Technical or other unfamiliar terms are underlined when used the first time, and are included in the glossary (Appendix A).

Quotation marks are used to indicate the exact spelling of a word, or the way a word should appear on a line typed by a user. For example, part of a person's identification on Multics is called a Person_id, and that term is unquoted, but a specific example of it, say "PSissle", is quoted. You do not type these quotation marks.

Another convention within examples is the use of an exclamation point to indicate lines you type. The exclamation point does NOT appear on your terminal - you do not type it, and Multics does not type it to prompt you. Exclamation points appear ONLY in examples, and ONLY to show which lines you type.

Line numbers and text within angle brackets (<...>) are used within examples for explanatory purposes ONLY. They are not actually typed by Multics, and they should not be typed by you.

MULTICS CONVENTIONS

Several characters have special meanings on Multics.

Two special characters are deletion characters that you can use to correct typing mistakes. To delete single characters, use the "#" character (called the erase character) directly after the characters you want deleted, one "#" for each character you want to delete. Thus this line:

is seen by Multics as:

The erase character, when used to erase a blank space, will erase ALL the blank spaces between characters. For example, this line:

is seen as:

because the first # erases the "s", the second erases the next row of 4 blanks, and the third erases the "i".

The "@" character (the kill character) deletes all characters to the left of it on the line; for example:

is seen as:

You should avoid some characters unless you are specifically instructed that you may use them. These are:

You will learn about the correct use of these characters in Part 2.

On Multics, names are not allowed to contain blank spaces. If a name consists of more than one word, the "_" (underscore) character is used to separate the words. For example, the send message command name has an underscore connecting the two words. This convention is treated fully in Section 3.

Other characters have special meanings only in some contexts. Such characters are noted where necessary.

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