Some of the more common reasons that cause a Mac to run slowly include incompatible apps, limited memory or limited disk space and unnecessary startup apps. For example, if an app is incompatible, the operating system, or OS runs overtime trying to make it work.

The first thing a Mac owner should look at is if the hard drive is close to capacity. When the free space on the hard drive is too small, the OS does not work efficiently. To check the amount of space available, one simply goes to the Apple menu, selects "About This Mac," and then clicks on "More Info." To free up space, the user should delete any unnecessary files, as media files tend to take up the most space, and old downloads.

Incompatible applications and unnecessary startup apps are also common reasons for a sluggish Mac. Mac owners should check the documentation that came with the app to ensure it works with the computer's setup. There are programs and apps set to launch automatically when the computer starts. This causes a drain on the Mac's resources. Users should go to "System Preferences," then "Users and Accounts" to log in and see what items are set to launch automatically.