Extensions are small programs that "extend" the function of the Mac's Operating System. They reside in the Extensions folder inside the System folder. They run automatically at startup, and usually you can just ignore them. In fact, the ability of the Mac to painlessly take on new functions is due in part to the simple concept of Extensions. If you buy a new printer, scanner, modem, tape drive, or any new computer devices that might come along; just drop an Extension into your System folder and Presto!, your Mac knows how to run it. (Mac owners don't mess with DIP switches and AUTOEXEC.BAT or .DLL files for half of the night.)
However, as Macintosh computers have become more complex, particularly with PowerMacs and System 7.3 (and up), the number of Extensions in the Mac OS has ballooned. In addition, some software companies have created Extensions to boost the functionality of traditional applications (word processors, spreadsheets, graphics), and other companies have created utility Extensions (such as RAM Doubler) that profoundly affect the way your Mac works.
This huge number of Extensions has created several problems. First, each Extension is really a tiny program that is running in the background on your computer. Each Extension uses some RAM and some processor time, so lots of Extensions can really slow down your machine. Second, Extensions interact with your computers operating system in some rather fundamental ways. If you upgrade your System, it is likely that some Extensions will no longer work properly. Third, Extensions can conflict with each other, causing a wide variety of nasty problems on your computer. This is particularly a problem when you have a variety of Extensions created by several different third party developers (anyone other than Apple Computer). See the Extensions Conflicts section for a discussion of the diagnosis and solution for this problem.
In System 7.5, Apple introduced a new utility called the Extensions Manager to help manage the increasing number of Extensions (and Control Panels). Now rather than dragging Extensions into and out of folders, users can activate and inactivate Extensions by simply clicking on checkmarks. The Extensions Manager also allows the creation of sets of extensions for particular functions -- such as for using a scanner and graphics program or for playing a favorite game.
In System 7.6, the Extensions Manager has been substantially improved (although the look is a bit evocative of Windows95). A lot of the new features help in the organization of the ever increasing number of Extensions.
Among the most useful new features of the Extensions Manager are the column headers (On/Off, Name, Size, Version, Package) which also act as buttons, to sort the Extensions. View by Package is particularly useful since it lets you identify the source of each extension it is illuminating to see all the "bloat" Microsoft deposits in your System when you simply asked to install a program.
And for those of us who have to solve Extensions conflicts often, that new Restart button right in the Extensions Manager window is a handy little shortcut.
Another good feature is the "Show Item Information" option at the lower left of the Extensions Manager window. When this triangle is clicked the Extensions Manager window expands to show the usual information from the "Get Info" box [Command + I] plus an added field that is meant to explain what the Extension does. This feature is not utilized to its fullest yet, since all Extensions will have to be updated to include this additional information. It would be great to see this fully implemented to help decipher what all these Extensions are that programs automatically deposit on your system.
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