Q: is there a utility that will diagnose and repair a slow iMac

Things You Can Do To Resolve Slow Downs

If your computer seems to be running slower here are some things you can do:

Start with visits to:     OS X Maintenance - MacAttorney;

                                  The X Lab: The X-FAQs;

                                  The Safe Mac » Mac Performance Guide;

                                  The Safe Mac » The myth of the dirty Mac;

                                  Mac maintenance Quick Assist.

Boot into Safe Mode then repair your hard drive and permissions:

Repair the Hard Drive and Permissions Pre-Lion

Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

Repair the Hard Drive - Lion/Mountain Lion/Mavericks

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the Utilites Menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD disk icon and click on the arrow button below.

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported, then click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu. Select Restart from the Apple menu.

Restart your computer normally and see if this has helped any. Next do some maintenance:

For situations Disk Utility cannot handle the best third-party utility is Disk Warrior;  DW only fixes problems with the disk directory, but most disk problems are caused by directory corruption; Disk Warrior 4.x is now Intel Mac compatible.

Note: Alsoft ships DW on a bootable DVD that will startup Macs running Snow Leopard or earlier. It cannot start Macs that came with Lion or later pre-installed, however, DW will work on those models.

Suggestions for OS X Maintenance

OS X performs certain maintenance functions that are scheduled to occur on a daily, weekly, or monthly period. The maintenance scripts run in the early AM only if the computer is turned on 24/7 (no sleep.) If this isn't the case, then an excellent solution is to download and install a shareware utility such as Macaroni, JAW PseudoAnacron, or Anacron that will automate the maintenance activity regardless of whether the computer is turned off or asleep.  Dependence upon third-party utilities to run the periodic maintenance scripts was significantly reduced since Tiger.  These utilities have limited or no functionality with Snow Leopard or later and should not be installed.

OS X automatically defragments files less than 20 MBs in size, so unless you have a disk full of very large files there's little need for defragmenting the hard drive.

Helpful Links Regarding Malware Protection

An excellent link to read is Tom Reed's Mac Malware Guide.

Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.

See these Apple articles:

          Mac OS X Snow Leopard and malware detection

          OS X Lion- Protect your Mac from malware

          OS X Mountain Lion- Protect your Mac from malware

          About file quarantine in OS X

If you require anti-virus protection I recommend using VirusBarrier Express 1.1.6 or Dr.Web Light both from the App Store. They're both free, and since they're from the App Store, they won't destabilize the system. (Thank you to Thomas Reed for these recommendations.)

Troubleshooting Applications

I recommend downloading a utility such as TinkerTool System, OnyX, Mavericks Cache Cleaner, or Cocktail that you can use for removing old log files and archives, clearing caches, etc. Corrupted cache, log, or temporary files can cause application or OS X crashes as well as kernel panics.

If you have Snow Leopard or Leopard, then for similar repairs install the freeware utility Applejack.  If you cannot start up in OS X, you may be able to start in single-user mode from which you can run Applejack to do a whole set of repair and maintenance routines from the command line.  Note that AppleJack 1.5 is required for Leopard. AppleJack 1.6 is compatible with Snow Leopard. Applejack does not work with Lion and later.

Basic Backup

For some people Time Machine will be more than adequate. Time Machine is part of OS X. There are two components:

1. A Time Machine preferences panel as part of System Preferences;

2. A Time Machine application located in the Applications folder. It is

    used to manage backups and to restore backups. Time Machine

    requires a backup drive that is at least twice the capacity of the

    drive being backed up.

Alternatively, get an external drive at least equal in size to the internal hard drive and make (and maintain) a bootable clone/backup. You can make a bootable clone using the Restore option of Disk Utility. You can also make and maintain clones with good backup software. My personal recommendations are (order is not significant):

  1. Carbon Copy Cloner

  2. Get Backup

  3. Deja Vu

  4. SuperDuper!

  5. Synk Pro

  6. Tri-Backup

Visit The XLab FAQs and read the FAQ on backup and restore.  Also read How to Back Up and Restore Your Files. For help with using Time Machine visit Pondini's Time Machine FAQ for help with all things Time Machine.

Referenced software can be found at MacUpdate.

Additional Hints

Be sure you have an adequate amount of RAM installed for the number of applications you run concurrently. Be sure you leave a minimum of 10% of the hard drive's capacity as free space.

Add more RAM. If your computer has less than 2 GBs of RAM and you are using OS X Leopard or later, then you can do with more RAM. Snow Leopard and Lion work much better with 4 GBs of RAM than their system minimums. The more concurrent applications you tend to use the more RAM you should have.

Always maintain at least 15 GBs or 10% of your hard drive's capacity as free space, whichever is greater. OS X is frequently accessing your hard drive, so providing adequate free space will keep things from slowing down.

Check for applications that may be hogging the CPU:

Pre-Mavericks

Open Activity Monitor in the Utilities folder.  Select All Processes from the Processes dropdown menu.  Click twice on the CPU% column header to display in descending order.  If you find a process using a large amount of CPU time (>=70,) then select the process and click on the Quit icon in the toolbar.  Click on the Force Quit button to kill the process.  See if that helps.  Be sure to note the name of the runaway process so you can track down the cause of the problem.

Mavericks and later

Open Activity Monitor in the Utilities folder.  Select All Processes from the View menu.  Click on the CPU tab in the toolbar. Click twice on the CPU% column header to display in descending order.  If you find a process using a large amount of CPU time (>=70,) then select the process and click on the Quit icon in the toolbar.  Click on the Force Quit button to kill the process.  See if that helps.  Be sure to note the name of the runaway process so you can track down the cause of the problem.

Often this problem occurs because of a corrupted cache or preferences file or an attempt to write to a corrupted log file.

What year, screen size, CPU speed and amount of RAM installed?

To find out info about your system,

Click on the Apple symbol in the upper left of the OS X main menu bar. A drop down menu appears.

Click About this Mac. A smaller popup window appears. This gives you basic info like what version of OS X your iMac is running, the speed of your iMac's CPU and how much RAM is installed.

Click on the button that says More Info. A larger window appears giving you a complete overview of your iMac's hardware specs.

Highlight all of this info and copy/paste all of this into another reply to this post, editing out your iMac's serial number before actually posting the reply.

This will tell us everything about your iMac so we may begin to help with your iMac issues.

How full is your Mac's hard drive?

Locate your iMac's hard drive icon on the OS X desktop. Click the icon once, then use the keyboard key combination Command-I. This will give you additonal info about your iMac's internal hard drive.

Copy/paste this info, also, into this reply.

Do you run any antivirus software on your Mac? Antivirus software can slow down the normal operation of OS X and cause Mac OS X performance issues and /or other adverse system issues.

Do you have apps like MacKeeper or any other maintenance apps like CleanMyMac 1 or 2, TuneUpMyMac or anything like these apps, installed on your Mac?

These types of apps, while they appear to be helpful, can do too good a job of data "cleanup" causing the potential to do serious data corruption or data deletion and render a perfectly running OS completely dead and useless leaving you with a frozen, non-functional Mac.

Plus, these type of apps aren't really necessary.

They really aren't.

There are manual methods to clear off unnecessary data off of your Mac that are safer and you have complete control over your Mac and not just leave a piece of auto cleaning software in charge of clearing off data off of your Mac.

Their potential of causing OS X issues outweighs the implied good and benefits these types of hard drive or memory "cleaning" apps are written to do.

Plus, the software company's that write these apps make it hard to easily uninstall these apps if something DOES go wrong and these apps work in a way where you have no recovery or revert function to return your Mac back to its former, working state in the event something does go wrong.

It is best to never download and install these types of apps.

The risk to your system and data is too great a risk!

Completely uninstall these types of apps either by trying the instructions giving from the developers' websites'. or doing a web search for the correct way to uninstall these types of apps.

You may need to update all of your third party software if there are OS X Mavericks updates that can be applied. You may need to, ACTUALLY, go to the third party developers' websites if there are no updates through the Mac App Store.

Update all of your Web browser Internet plugins, also.

Also, if you have any connected third party devices, like non-Apple, third party keyboards, mice, drawing tablets, hubs, card  readers, etc, you need go to the device makers' websites to update the drivers for these devices to OS X Mavericks compatible versions if they are available and/or needed.

Can I check the speed of the internet connection?

You can check w/your ISP and the website Speedtest

Check out the following & do the necessary: 

User Tip:  Why is my computer slow?

What to do when your computer is too slow

Speeding up your Mac