I use a Mac and recently trashed my entire system by accident. After reinstalling everything, I could not remember the names and locations of several useful items I had downloaded from the internet. What should I do? Name and address supplied DQ: Your problem has probably happened to most of us. You have a few options for this. When you download an application, it will usually go into a folder on your Mac called Downloads. This fills up over time and you probably empty it when needed. A better idea would be to save the folder's contents in a way that allows you to recreate your system. Most downloaded files will have .zip, .pkg or .dmg filename extensions. Double-clicking on these normally starts the installation process. (The .zip files will create a folder inside which there will be .pkg or .dmg files.) After you install the software, you should copy the original file into a folder you have created called something like Installations. When that folder gets too big, you should save it to a DVD recordable disc if you can - renaming it 'InstallationDecember2008', or similar. You could also write a note in the TextEdit program for each file, explaining when and why you installed it. You will find this useful later when you forget where things have been placed in your computer. This may be old-fashioned, but I like to use the Terminal application on my iMac to interact with the computer through a command line interface in lieu of the mouse. Sometimes it tells me I need to be a 'root user'. What does that mean and how can I be one? Robert, Mui Wo DQ: The root user, sometimes called the 'super user', is the administrator account in the Mac OS X operating system providing read and write privileges to all areas of the file system. Although you already administer your machine, this account is closer to the entrails of the system and thus, has a higher status. On the Terminal application, you may type 'ls' to get a list of files. But if you type 'su ls', you will be prompted for a password. That means the system is asking for your 'super user' account password. To set this up, go to the Applications folder and then the Utilities folder. There is an application called Directory Utility. Double-click on that then click on the button that says Show Advanced Settings. After clicking on Edit, you will see Enable Root User. If it is grey instead of black, you will first have to click on the lock at the bottom left of the window, type in your administrator password and then go back to enable the root user.