Step 14 of 20: Get rid of desktop clutter
Every file on your desktop is a window with an image in it - either an icon or a preview of the file. Each of those windows and their contents is stored in RAM so that when you switch to the Desktop or use QuickLook, your Mac can show you what's in the window. In other words, the more files you have on your desktop, the more data is stored in RAM. That could result in your Mac running more slowly, especially if your Mac's memory is already under pressure.
Organise files properly in the appropriate user folder - Documents, Pictures, Movies etc - and you may see an improvement in the speed of your Mac.
Step 15 of 20: Restart regularly
Macs are so stable and so power-efficient when they sleep that most of us don't bother shutting them down regularly, especially if they are notebooks. That means caches don't get flushed and applications that hog RAM don't let it go.
Restarting your Mac clears the caches and shuts down applications. The result is a Mac that's refreshed and should perform better.
Step 16 of 20: Manage Spotlight
Spotlight, particularly in recent versions of OS X, is a terrific tool. But if you use multiple drives, particular on older Macs, it can take Spotlight to index and re-index the filesystem. That in turn will slow down your Mac.
The answer is to manage Spotlight to limit the files it indexes. This is done in the Spotlight pane in System Preferences. Once you've opened the pane, click on the Privacy tab. You can now drag any folders or volumes that you don't need to search on to the window. That will stop Spotlight indexing the folder or volume and thus reduce the number of files it needs to index, meaning it spends less time indexing and should improve performance on your Mac.
Step 17 of 20: Make your own Fusion drive
Most of the current crop of Macs come fitted with SSD storage in place of a hard drive. SSD is smaller, uses less power, and significantly faster than a hard drive. It's also, however, more expensive per GB.
To provide inexpensive high capacity storage alongside the speed benefits of SSD, Apple came up with the Fusion drive - an SSD and a hard drive that your Mac sees as one volume, but which keeps the system and applications on the fast SSD while putting documents, photos, music and video on the hard drive.
You can make your own fusion drive if you have a spare hard drive bay in your Mac, or if you have an optical drive you don't need. The instructions on how to do it are here.
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