In music and computers an extension can very loosely be thought of as the Macintosh equivalent to a driver in the PC world. Extensions are little bits of software that are loaded into the RAM of your Mac when it boots. They provide added functionality to your basic Mac OS. Many peripherals that connect to a Mac require a special extension to operate. This would include digital cameras, MIDI interfaces, modems, fax software, your Palm Pilot, enhanced track balls, digital audio software and hardware, graphics tablets, and the list goes on and on. Extensions create a conduit for the special communication that must take place between the CPU and these devices. Current versions of the Mac OS include an Extensions Manager Control Panel that allows the user to manage which extensions are active and get loaded upon boot up. There are other third party programs that allow even more flexibility, and include the ability to change the order in which they load. These tools exist because extension conflicts – incompatibilities between different extensions – are a common problem with Macintosh computers. Extension conflicts can cause crashes and all kinds of undesirable behavior in your Mac so it’s important to keep an eye on what is installed and loaded into your machine. The Extensions Manager helps with this, but the Mac will also display the icon for most of the active extensions and control panels along the bottom of the screen when it is booting. This is handy for just keeping an eye on what is happening. Any time you install new software on your Mac there is the potential to have new extensions and control panels installed. A good clue that this has happened is when the installation is complete you get a dialog box indicating you need to restart the computer in order to use the new software.