My iMac is very slow and experiencing many freezes

Hi Kathy,

Welcome to the Support Communities! I believe you are asking about the Disk Utility application which has a "First Aid" tab. The information on how to use it is outlined below:

Resolve startup issues and perform disk maintenance with Disk Utility and fsck - Apple Support

http://support.apple.com/en-gb/HT203176

Try Disk Utility

Use these steps to use the Disk Utility app to verify or repair a disk.

1. If you're using OS X Lion or later, start the computer from Recovery System or Internet Recovery. If you're using an older version of OS X and your computer came with a Mac OS X Install disc, insert the installation disc and restart the computer while holding the C key instead.
2. When your computer finishes starting up, choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Startup Disk (usually named "Macintosh HD").
6. Click Repair. Disk Utility checks and repairs the disk.

Tip: With Mac OS X v10.6 and earlier, always start up your computer from an Install or Restore disc when using Disk Utility to verify or repair your startup volume. Otherwise, you might see some disk error messages.

Here are some other things to try if your Mac is running slowly:

OS X Mavericks: If your Mac runs slowly
http://support.apple.com/kb/PH13895

If you find your Mac is running slowly, there are a number of potential causes that you can check.

• An app you’re using may require more memory than your computer has easily available. To see how much memory your computer has, choose Apple menu > About This Mac. See the help that came with the app to find out what it requires. To find out how to increase your computer’s memory, see the documentation that came with your computer.

  Find the manual for your Mac

• Quit any app that isn’t compatible with your computer. For example, an app may require a different processor or graphics card. See the documentation that came with the app to find out what it requires.

  • To see what processor your computer has, choose Apple menu > About This Mac.

  • To see what graphics card your computer has, choose Apple menu > About This Mac, click More Info, then click Displays.

• Your computer’s startup disk may not have enough free disk space. To make disk space available, move files to another disk, then delete files you no longer need on the startup disk.

  Increase disk space

• Quit any apps you’re not using.
• Use Disk Utility to verify and fix any issues with your hard disk.

  If you have problems with your disk

• Use Activity Monitor to see if a particular app or activity is making a large demand on your Mac.

I hope this information helps ....

- Judy