It happens to every Mac user sooner or later. The virtual gears inside your computer begin to act as though they're running in a vat of tapioca pudding. No matter what you try to do, your Mac moves at a pace that a snail could run circles around. But before carting your Mac off to an Apple Genius Bar, try these fixes.
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Restart your Mac
One of the simplest steps you can take is also one of the most effective. Restarting your Mac cures most slow-downs, because it forces background processes to quit, frees up RAM, and generally lets you begin afresh.
Check your Internet connection
For many Mac users, a slow Internet connection is synonymous with a slow computer. That's because almost everything they do--from surfing the Web to checking email--requires Internet access. If your online activity seems to be moving at a crawl, improving your connection can solve your problem.
Check Network preferences: Do you see a spinning beachball in Safari when you try to load webpages? It may not be clear at first whether pages are taking an unusually long time to load or whether your connection is actually broken. Select Apple menu > System Preferences, and choose Network. Click Assist me and then Diagnostics, choose your connection type, and then click Continue to run the tests. If a problem pops up, follow the Network Diagnostics tool's suggested advice for dealing with it.
Check your speed: If you can get the page to load, go to a site that tests Internet connection speeds. Since I use Comcast Internet service, I go to Comcast Speed Test. Other options include Speedtest.net and TestMySpeed.com.
You probably pay for certain upload and download speeds--look at your bill or check with your ISP to see what those speeds are supposed to be. If you detect a slowdown, call your ISP to ask if it is experience general problems that may be affecting you. If so, you'll have to wait for someone else to correct the issue. Alternatively, your ISP may offer to check and perhaps fix your modem connection via remote commands.
Test all your Macs: If you have more than one Mac, test the Internet speed on all of them. If the slowdown occurs on only one machine, the problem most likely originates with that Mac. It may, for instance, have an unusually weak Wi-Fi connection. If so, you may be able to put things right by turning Wi-Fi off and then back on. To do so, go to the Wi-Fi menu in the menu bar and select Turn Wi-Fi Off. Wait a few seconds and then turn it back on.
Disconnect and reconnect your modem: Unplug your Internet modem and wait for about 10 seconds. Plug it back in. If you have a separate router, such as an AirPort Extreme, do the same with the router. Wait for everything to reboot. Check your speed again.
Free up disk space
To function at a decent pace, OS X needs to have adequate free space on your startup drive. If your Mac's available disk space shrinks to near zero, the system will become very sluggish (as I covered in a Bugs & Fixes column).
Check disk usage with Activity Monitor: One way to check the amount of free disk space on your Mac is to launch Activity Monitor (included with OS X in the /Applications/Utilities folder) and click the Disk Usage tab at the bottom. My rule of thumb is that a system should have at least 10GB available (or 10 percent of its drive's capacity, whichever is smaller). If your Mac's free space falls below this threshold, you'll need to clear some additional space.
Search for large files: An easy way to locate big files that you may no longer need is to use Spotlight. In the Finder, press Command-F, click the plus (+) sign, click the Kind pop-up menu, and select Other. Select File size from the resulting list, and then click OK. Set up the criterion to read File Size is greater than 500MB. If nothing of consequence appears when you run that search, select a smaller file size and try again. Or try a utility such as Id-design's $13 WhatSize. Delete any files that you no longer need.
Delete cache and log files: Ordinarily, cache files, such as those in the ~/Library/Caches folder, help your Mac run faster. If you delete them as a quick fix, your system will rebuild them later. Log files, such as those in the ~/Library/Logs folder, keep track of past events on your Mac, such as past crash reports. Most users never look at these files, so you can probably delete them with no adverse consequences.