# Introduction

One feature you're almost guaranteed to find in a UNIX-based operating system is a system of user accounts. This feature is designed for computers that are used by more than one person.

## Why Accounts?

Picture this: a family of four shares one iMac. Fourteen-year-old Andrew imports his collection of punk rock CD's into the computer's iTunes library. All of a sudden, the music is on every other family member's iPod. Seven-year-old Alice wants to have a Barbie desktop picture, but the other family members would rather not. All of Andrew's friends are mixed in with the father Mark's business contacts in Address Book.
In other words, total chaos.
Accounts to the rescue! Each user with an account gets their very own private:
* "Home Folder" for storing personal documents and other files.
* Preferences and settings for Mac OS X and individual applications.
* iTunes library, iPhoto library, Address Book, iCal Calendar, Safari Bookmarks, iChat buddies, etc.

## Deciding How You Will Use Accounts

An account is kind of like an entire "version" of the computer. Our family of four could create an account for each child. Andrew gets his own music collection and contacts. Alice gets her Barbie desktop picture. And everyone is happy.
Unfortunately, the system of accounts can be a double-edged sword. Let's say that the two parents create separate accounts. Which account will keep the family photos? Which will keep the parents' shared music collection? Things can start to get complicated.
Don't be afraid to get creative with your system of accounts. In this case, the perfect solution is to create a fifth account: "Family". This account is in charge of the family address book, family music library, family photos, etc. With five accounts for the four users of the iMac, nobody gets in anyone else's hair, and yet everyone can access the files they want to.
Your solution may be different than the hypothetical family above. Come up with several different possibilities and weigh their advantages and disadvantages. Consider limits that need to be placed on users, what data needs to be easily accessible to all users, and the varying privacy needs of each user. Try to get it right the first time; creating accounts is easy, but modifying accounts is more difficult.

## Types of Accounts

* Standard
** This should be your daily use account.
* Administrator (Super User)
** The person who manages the computer should have this account *in addition* to their own standard account.
* Root
** Most people will never need to access this type of account, but certain high-level management tasks require this level of access.

# Adding an Account

The central control panel for the Account system is the Accounts pane of System Preferences. This pane lets you add, modify, and remove user accounts. To adjust the more serious settings in this pane, you'll need to unlock it with an administrator password. Only an administrator can mess with the account system.
The sidebar on the left lists the accounts on your Mac. Your account is at the top, and everyone else's appears underneath. To add an account, click the plus button underneath this sidebar. A sheet appears, prompting you for some information to set up the account:
* Name - Type in a name for the account.
* Short Name - If the user is ever prompted for their name and password, then they can use this name instead. Keep the short name simple and in all lowercase letters. For instance, John Doe's short name should be "john".
* Password - Depending on how sensitive information in this account is, you may wish to create a password. In a family setting, passwords are usually unnecessary for most accounts, and this field can be left blank.

# Fast User Switching

Fast User Switching is a feature Apple "borrowed" from Windows that lets two users stay logged in at the same time. Keep in mind that having multiple users simultaneously logged in with applications running will require a large amount of memory.