Slow operation and generally unusual behavior are signs that may indicate that permissions need to be repaired on your Macintosh's hard drive. To do so you can run Repair Disk Permissions from within Disk Utility, located on your hard drive at: Applications/Utilities/Disk Utility

Note: There is no need to verify permissions before you repair them. Unless you can read the report and understand what Disk Utility proposes to do, there is little point in verifying first.

You should run Repair Disk Permissions regularly. Maybe once a month, and every time after you have installed new software.  (Contrary to popular belief, it is not at all necessary to run Repair Disk Permissions prior to installing new software.  Though doing so won’t hurt anything.)

Open Disk Utility, and on the left side of the screen select your hard drive, then select the First Aid tab on the right side and click on "Repair Disk Permissions."

See: 

http://support.apple.com/kb/PH5821
and
http://support.apple.com/kb/HT1452
and
http://support.apple.com/kb/HT2963
for further details.

Note: Some users are reporting that they run Repair Permissions over and over again, and the same permissions are reported as being incorrect, and they are not being repaired. You should know that, in addition to reporting faulty permissions, until very recent versions of OS X, running Repair Permissions in Disk Utility also gave you advisory messages. For instance, it might report that it is using an updated set of rules to determine if any permissions needs to be repaired. These are not error reports and they will not change no matter how many times you run Repair Permissions. Advisory messages do not indicate that anything is wrong, and they can safely be ignored. Example:

"We are using special permissions for the file or directory
./System/Library/Filesystems/hfs.fs/hfs.util.
New permissions are 33261"

or

"ACL found but not expected" or “Warning: SUID file” error messages
http://support.apple.com/kb/TS1448
These messages can safely be ignored.

Note: Some users have noted that their permissions revert to apparently incorrect settings every time that they restart their Macintosh.  Disk Utility/Repair Disk will correct their permissions, but the next time that they restart the permissions have been changed again.  This has been traced to the fact that these users are running security software such as Intego’s Virus Barrier.  The security software is intentionally modifying permissions to close off potential malicious exploits.  Note that in this case, it is neither necessary, or even desirable, to repeatedly repair your permissions to “fix” this situation.

Update: As of OS X 10.7 (Lion) there is a way to repair more permissions; those in your User home folder:

1. Restart Lion, and before you hear the chime, hold down the Command and R keys.

2. You’ll be at the Repair Utilities screen. Click the Utilities item in the Menu Bar, then click Terminal.

3. In the Terminal window, type “resetpassword” and hit Return.

4. The password reset utility window launches, but you’re not going to reset the password. Instead, click on the icon for your Mac’s hard drive at the top. From the dropdown below it, select the user account for which you want to repair permissions.

5. At the bottom of the window, you’ll see an area labeled Reset Home Directory Permissions and ACLs. Click the Reset button there.

The reset process takes just a couple of minutes. When it’s done, close everything and restart your Mac.

http://blog.chron.com/techblog/2011/09/want-to-really-repair-permissions-on-your-
mac-try-this/
http://www.macobserver.com/tmo/article/os-x-repair-home-folder-permissions

Discussion.

Maintenance Myth #1: "You need to repair permissions from a copy of Disk Utility that resides on the drive that you are repairing."
This is a myth that is very prevalent.

It used to be that you were warned against repairing permissions on one disk while booted from another because only the receipt files on the drive you were booted from would be consulted, not the receipt files on the drive you were repairing, and thus not all permissions would be set correctly. This is no longer necessary. As of late in OS X 10.2, you could run Repair Permissions while booted from a disk other than the one that you are repairing (e.g. the OS X installer CD-ROM), and it will correctly use the receipts on the disk being repaired.

http://support.apple.com/kb/HT1452

Maintenance Myth #2: There are some folks who are very adamant that you never need to repair permissions under OS X. While repairing permissions isn't a panacea, they are wrong, it is definitely worth your while to repair permissions occasionally. The reality is that Repairing Permissions doesn't require that you purchase anything to do it, it can be accomplished fairly quickly, it doesn't hurt anything, and after repairing permissions sometimes the problem(s) that the user is experiencing are gone. In addition, often the curative effects of repairing permissions are repeatable and predictable. I don't see any reason not to do it.

Apple provides a list of reasons that you may need to repair permissions:
http://support.apple.com/kb/HT2963

Here is a (rather extreme) example of the "it's never ever necessary" school of thought:

Exercises in Futility Part 2: Repairing Permissions is Useless
http://www.unsanity.org/archives/000410.php

From the folks at MacFixIt, who recommend routine repair of permissions:

Another follow-up to the Repair Permissions debate
http://reviews.cnet.com/8301-13727_7-10331125-263.html?tag=mfiredir

The MacFixIt article makes this excellent point: While Disk Utility's Repair Permissions feature only repairs permissions for Apple Software (and not any third party software), much of that Apple software is system software, and that system software contains routines that are accessed and used (and used often) by third-party applications. Thus, incorrectly set permissions, contrary to what some would tell you, can cause problems with third-party applications.

These MacFixIt articles further explain what repairing permissions does, and they document real-world cases where repairing permissions was extremely helpful to users.:

Unraveling the Repair Disk Permissions controversy
http://reviews.cnet.com/8301-13727_7-10331113-263.html?tag=mfiredir

Repair Permissions Success Stories
http://reviews.cnet.com/8301-13727_7-10331714-263.html?tag=mfiredir

More Repair Permissions Success Stories
http://reviews.cnet.com/8301-13727_7-10331718-263.html?tag=mfiredir

Frequently Asked Questions On Fixing Permissions In OS X
http://www.macissues.com/2014/10/29/faq-on-fixing-permissions-in-os-x/

Microsoft Office, and especially Microsoft Word, often requires, and responds very well to repairing permissions:
http://word.mvps.org/Mac/DiskIssues.html

Return to Table Of Contents

OS X runs its own built-in maintenance routines, sometimes called "cron jobs", or "maintenance scripts", automatically between 3:00 am and 5:30 am each day. (There are daily, weekly and monthly scripts).
http://support.apple.com/kb/HT2319
The thing is that these scripts do just about nothing of great importance.  If they don't run for weeks, or even months, it's just not a big deal.  So, despite the fact that these are called "maintenance routines," don't get concerned if they haven't run in a long time.  Don't ignore this entirely, though, because if your Mac has a minor problem, in time failure to run the maintenance scripts will allow your Mac's hard drive to fill up with a bunch of invisible log files filled will message about that minor problem.

You can find a rundown of what the built-in maintenance routines do at:
http://arstechnica.com/civis/viewtopic.php?f=19&t=454874
https://discussions.apple.com/message/8906776#8906776

Prior to OS X 10.5, if you didn't leave your computer on 24 hours a day, or if you left it on but you let it go into sleep mode at night, these routines weren't run.   As of OS X 10.5 and later your Mac will run its maintenance scripts automatically at the next available opportunity if you put your Mac into sleep mode all night.  Though the scripts still won't run if you shut your Macintosh down at night.
http://discussions.apple.com/message.jspa?messageID=6552347
http://discussions.apple.com/thread.jspa?threadID=2143195&tstart=0
http://developer.apple.com/macosx/launchd.html
NOTE: As of OS X 10.5 the maintenance scripts are no longer handled by the UNIX facility "cron", they are now handled by a similar facility called "launchd," if that means anything to you.

NOTE: If you decide that you want to run the maintenance scripts manually, you can use this free utility:

Maintidget (Maintenance Scripts Widget)
http://www.giantmike.com/widgets/Maintidget.html

or

Onyx:
http://www.titanium.free.fr/
In Onyx:
Maintenance tab --> Scripts

Discussion.

If you want to be sure that the built-in maintenance tasks have been run, the daily, weekly and monthly maintenance scripts each write the details of every run into their own log file, which you can check. Open the Console application (located at: Applications/Utilities/Console), go to:
File --> Open Quickly --> /var/logs/. Select "daily.out", "weekly.out" or "monthly.out" for the maintenance logs.

Return to Table Of Contents

Even though running the routine maintenance scripts clears out some temporary files, none of the system caches are touched by them. Occasionally caches become corrupted, impacting the performance and stability of your Mac.  So it is a good idea to every rare now and then use a utility that clears the system caches, and/or your Internet browser caches. Deleting caches won't hurt anything. However, over time a cache speeds up your computer (assuming that you do some things repetitively), so if you aren't experiencing any problems, you should probably leave your caches alone. On the other hand, if it has been ages since you have flushed your caches, or if your computer is running slowly, or if you are experiencing odd problems, it might be a good idea to flush them. Use your discretion.  (In other words, this isn't something that you should be doing every day, or every week, or even every month.)

Onyx is a free program which, among other useful things, cleans out system and Internet browser caches.  You can get Onyx from:
http://www.titanium.free.fr/
In Onyx:
Cleaning tab --> Internet --> Browser cache --> Download cache
Automation tab --> Cleaning

Application caches are easily uninstalled or trashed manually, but should probably be limited to instances where an individual application is running slowly or erratically:
http://support.apple.com/en-us/HT201516

Note that Booting into Safe Disk mode automatically clears the Apple ATS (Apple Typographic System) font caches. However it doesn't clean out other kinds of caches.

Discussion.

According to MacAddict, October 2005, page 20, it is a good idea to occasionally clear out application-specific caches. They specifically recommend clearing out the two main cache folders in Mac OS X.

While Apple doesn't recommend doing this routinely, they indicate that it is a good idea in certain situations:
http://support.apple.com/kb/HT1199

A MacOSXHints tip also suggests clearing out the application cache files occasionally:
http://www.macosxhints.com/article.php?story=20060111202501460

This hint notes that there may be quite a few extraneous cache files in your cache folders and that clearing your caches (if you have been using your computer for some time) may save a lot of disk space.

Return to Table Of Contents

I recommend that you occasionally restart your Mac, and hold down the Shift key right after the startup chime is played, and keep it held down until the spinning black bar cursor appears.  There is  no need to hold down the Shift key past the time that the spinning bar cursor appears.
http://support.apple.com/kb/HT1455?viewlocale=en_US
This procedure invokes what Apple calls a "Safe Boot":
http://support.apple.com/kb/TS1417
and your Mac will report that it has been booted (started up) into Safe Boot mode. During startup in Safe Boot mode your Mac will do a file system check, entirely in the background, with no working status indicated, or report generated, and any problems will automatically be repaired.
http://support.apple.com/kb/HT1564?viewlocale=en_US
It may take a while for your Mac to start up in Safe Boot mode. Be Patient.  Once it has fully started up, you should immediately restart your Mac normally, because certain files are deactivated when you startup in Safe Boot mode.

Note: A wireless or Bluetooth keyboard might make it difficult to startup in Safe Boot mode.  
http://reviews.cnet.com/8301-13727_7-57570572-263/how-to-manage-os-x-boot-
options-with-wireless-keyboards/

Update: Some recent models of Mac seem to have depreciated Safe Mode and/or won't let you boot into it.
https://discussions.apple.com/thread/5485131?start=0&tstart=0
https://discussions.apple.com/thread/3750015?start=0&tstart=0

Apple indicates that there still is a Safe Boot mode in Yosemite:
http://support.apple.com/kb/PH18760
but some users report not being able to startup into Safe Boot mode in Yosemite.

Instead you may prefer (or need) to check your hard drive, and repair any problems, by starting up in "Recovery mode" (by holding down Command-R during startup) and then running Disk Utility/Repair Disk:
http://www.macworld.com/article/1167870/hands_on_with_mountain_lions_os_x_
recovery_and_internet_recovery.html
http://support.apple.com/kb/HT4718

Discussion.

Longtime Macintosh users know that under OS 8 and OS 9, if you were experiencing nasty problems with your hard drive, that running Apple's Disk First Aid usually didn't fix them. In such cases, users often resorted to using the commercial product Disk Warrior, which could perform near miraculous feats of repair on your hard drive. It was also an invaluable tool for routine preventative maintenance. Under OS X, Disk Utility/Repair Disk is the replacement for Disk First Aid. So, the question most folks have is, 'is Disk Utility/Repair Disk as lame as Disk First Aid, and is Disk Warrior still an invaluable utility to have?' There is an interesting thread on TidBits Talk that covers this topic:
Looking for Disk Warrior Justification
http://tidbits.com/article/8514

The answer is that Disk Warrior is a marvelous tool...when you need it. Fortunately, under OS X you just about never need it. For instance, you don't need to run Disk Warrior routinely as a preventative measure. (Though doing so, if you already own Disk Warrior, isn't a bad idea.) OS X is plenty stable without having to constantly rebuild its directory. And so, in my opinion, there is no need to purchase Disk Warrior (for about $100) unless a situation arises where Disk Utility/Repair Disk reports that it can't repair a problem with your hard drive. This is not to demean Disk Warrior. When you do need Disk Warrior, because your disk directory has developed errors that Disk Utility can't fix, it is a godsend to have.
http://www.alsoft.com/DiskWarrior/

For further information about disk repair software, have a look at:
http://db.tidbits.com/getbits.acgi?tbart=07451,
with a follow-up on TechTool Pro at:
http://db.tidbits.com/getbits.acgi?tbart=07696

There are other ways to run a file system check/Repair Disk under OS X, such as by running the command "fsck" from the Terminal, but these are more advanced ways to do exactly the same thing, that I don't think that the average user needs to know about.
For more information than you need, see:
http://support.apple.com/kb/TS1417 

Return to Table Of Contents

Macintosh Myth #3: Most folks with an opinion will probably tell you that Mac's running OS X never need to have their hard drives defragmented.

Here is a quote from a MicroMat technician, that I think is very insightful:
"The claim that installations of Mac OS X on HFS+ volumes do not fragment is a myth believed by people who do not have disk optimizers that allow them to see how much fragmentation their disks have. It is an example of ignorance that is not able to be removed by any amount of evidence. I think theologians call that 'invincible ignorance'. It is now a widespread form of the pollution of information space."
http://is.gd/5VKgNv

Actually, Some Macs running OS X can benefit quite a bit from defragmenting their hard drive. But not for the reason that you might expect. There is often little in the way of performance to be gained by defragmenting your hard drive. But defragmenting your drive can stave off some very flaky behavior, out of memory errors, and possibly even data loss.

OS X handles "file" fragmentation (a file being broken up into chunks and strewn across your hard disk) automatically, and fairly well, every time that you launch a fragmented file under 20MB.
http://article.gmane.org/gmane.comp.macosx.general/22906
http://forums.macrumors.com/archive/index.php/t-13383.html

But OS X doesn't handle "drive" fragmentation (small bits of free space between files) well at all. In fact, OS X is prone to huge amounts of drive fragmentation.

Drive (as opposed to file) fragmentation under OS X is mostly irrelevant with respect to performance, as long as it isn't severe. Where drive fragmentation becomes important is when there are no longer any large contiguous chunks of free space left on your drive for OS X to use for working space, for virtual memory, temp files, databases, etc. When this happens, OS X can start acting flaky, and eventually, in extreme cases, it will suffer from data loss.
http://www.cnet.com/news/does-mac-os-x-need-a-disk-defragmenteroptimizer/

I used to recommend that folks defragment their hard drive when it was approaching 80% full (no matter how large the drive is), because I've heard from so many folks who were experiencing out-of-memory errors and flaky behavior at this level (no matter how large their drive was), and defragmenting invariably fixes the problem. But I've heard from a number of users who made heavy use of their drive, and they have experienced the problem as early as around 60% full. And other folks won't experience the problem until their drive is well over 80% full. Clearly how you use your drive makes a difference as to when, or if you run out of free contiguous space on your hard drive.

So now, instead of using a rough rule of thumb on when you should consider defragmenting your hard drive, what I recommend is that folks check to see how much free contiguous space there is on their drive routinely, once their drive is over 50% full. You can do this quickly and easily with the free demo version of iDefrag:
http://www.coriolis-systems.com/iDefrag.php

There is no need to purchase anything until and unless you need to. When you have no large chunks of free contiguous space left, you can expect problems to begin to appear if you don't defragment your drive. Note that if you let this problem advance too far, it may become impossible for any utility to work on your drive, protesting that there isn't enough free space on your drive for it to be able to run. (This despite the fact that you may have many gigabytes of "total" free space left on your drive.)

You may never need to defragment your drive (prior to purchasing a new one because the old one is becoming too full) or you may need to do so much earlier than you would expect, but by checking with one of these free tools you won't have to guess whether it is necessary or not.

If your drive needs to be defragmented, the "only" hard drive defragmentation utility that I recommend is iDefrag. (See my comments about other hard drive defragmentation utilities in Note 1. below) It is the only one that I know of that can optimize the files on your hard drive in a totally OS X-savvy way. OS X has a journal, a hot band, virtual memory, metadata, etc. to keep track of. It is very important that these things be located properly on the disk or performance will be compromised.
Technical data about the hot band and meta data on hard drives running OS X 10.4 and later:
http://developer.apple.com/technotes/tn/tn1150.html#HotFile

iDefrag is the only hard drive optimization tool that does this perfectly (despite what some of the other companies that make hard drive defragmentation tools say).

Another option, instead of defragmenting your hard drive with a software utility program, is to simply purchase a new, bigger hard drive; copy all of the data on the old drive to the new drive, and then reinitialize (i.e. wipe clean) the old drive and start over with it. Moving all of your data from one drive to another will automatically defragment your data. Though it won't optimize it.

You have to reinitialize your data on the old drive for this plan to work, because if you just move "some" data from your old drive to your new drive, the old drive will still be badly fragmented, and without defragmenting the old drive it will still probably be flaky. (That is, even if you free up some space on the old drive, there more than likely still won't be the large chunk of contiguous free space available that the OS needs to run properly.)

Defragmenting your hard drive prevents any unusual behavior from your OS because it creates contiguous space, combining fragments of space strewn all over your drive into one large chunk of space.

Note that clearing off data from your drive, even a large amount of data, without also defragmenting, may not create enough "contiguous" space to keep your Mac running well.

WARNING: You should never, ever, defragment a solid state hard drive (SSD) (Most recent Macbook's use SSD's for their speed and light weight.  Several other Mac models, including recent desktop models, occasionally have SSD's for their speed.) or a hybrid drive (hybrid drives are sort of a combination of an SSD and a rotating disk hard drive). 
http://helpdeskgeek.com/featured-posts/should-you-defrag-an-ssd/
http://www.coriolis-systems.com/blog/2009/04/real-world-fragmentation.php

SSD's themselves need no periodic maintenance.  There is built-in software in recent versions of OS X called TRIM that keeps them running at peak performance:
http://en.wikipedia.org/wiki/TRIM

Discussion.

Definition of Terms:
Types of fragmentation:
1) "File fragmentation, where file are broken up and are not contiguous
2) "Drive" fragmentation, where, though files may be contiguous, the free space on the drive is fragmented.

"Defragmentation" means that things (that is, data, e.g. files and applications, and free space) are made contiguous (that is, not broken up into small bits and strewn about at different places) on your hard drive.

"Optimization" means that not only is the drive defragmented, but data is put where it should be and.or is put where it will provide optimum performance.

Let's refer to files A, B, C and D, and free space "__".

Here is a drive with no file fragmentation. All the files are contiguous, but free space is fragmented. In other words, there is no file fragmentation but there is disk fragmentation:
AAAAA__BB__CCCCC__DDD_

Here is a drive with both the files and free space fragmented:
AA__BBA__CCCCCB__DDDAA_

Here is a drive with no file or free space (disk) fragmentation. All of the files are contiguous, and all of the free space is contiguous:
AAAAABBBCCCCCDDD__________

Now, take a look at that first example, where there is a lot of disk fragmentation even all of the files are contiguous. Have you ever run a Mac under OS X with too little RAM? It was a dog, wasn't it? That's because your Mac was hitting your disk in a big way, using virtual memory instead of RAM for tasks. Now, think of the effect that you might see if you forced your Mac to use hundreds of little spaces all over your drive to write virtual memory to, instead of having it written to one big contiguous space. That's why drive fragmentation is more important than file fragmentation.

OS X automatically defragments files. OS X doesn't do any drive defragmentation at all.

Note that if you actually defragment your hard drive as part of a routine maintenance program (rather than just keep track of how much free contiguous space is available), let's say every coupe of months, then it won't take long to defragment your drive each time, and any potential problem will never rear its head. In addition, you should be able to use close to every last gigabyte of space on your hard drive, and you will always have every last ounce of performance that your Mac can give you as as side benefit.

See Note #1 below for more information on file defragmentation.

Return to Table Of Contents

Hard drives are quite a bit more reliable these days than they were just a few years ago. Unfortunately, the old saying that "all hard drives die eventually" is still true. It would be nice to know in advance when a hard drive is going to fail. That way you would have time to backup your data before your drive ultimately met its end. S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is a feature built into most modern hard-drives that acts as an "early warning system" for pending drive problems. OS X 10.3 and above have this ability built-in, but it only works if the actual hard drive in your Mac has this technology built-in also. Disk Utility, which comes with OS X (it is in your Application/Utilities folder), under OS X 10.3 and above can tell you the S.M.A.R.T.-status of your hard-drive. Unfortunately, you have to remember to regularly launch Disk Utility to check this. (See below for free utilities that will automate this process.)

To check your drive's S.M.A.R.T.-status using Disk Utility, launch Disk Utility and select your internal hard drive in the left column. If at the bottom of the window it says "Verified," your drive is in good shape. If it says: "About To Fail" you need to:
1) Not shut down your computer and hard drive until you have done the following...
2) Back up your hard drive, which you should do immediately, if you haven't already done so.
Hard drives on their last legs often will finally fail by refusing to start up.

I've been told that there is no hope for an internal drive once it reports "Failing" as its S.M.A.R.T status. Its time to get a new drive.

Volitans' SMART Utility ($20 for a 10 copy license) is different from other similar utilities which only read the overall S.M.A.R.T. Status. SMART Utility goes farther and displays the individual attributes tracked by S.M.A.R.T in an easy to read format so that you can see their status and information, and it also uses its own internal algorithm based on those attributes to detect drives failing before S.M.A.R.T. normally would. This pre-fail detection can save your data well before S.M.A.R.T. has determined that the drive is failing.
http://www.volitans-software.com/smart_utility.php

Note: FireWire and USB hard drives (that is, external hard drives), even if their internal mechanism is S.M.A.R.T.-enabled, can't be checked for S.M.A.R.T. status using Apple's Disk Utility.  However, you might be able to check the S.M.A.R.T. status of your external hard drive by downloading the demo of SMART Utility:
http://www.volitans-software.com/smart_utility.php
After installing SMART Utility you will need to install the optional SAT SMART Driver (from the SMART Utility menu) in order to see any external drives. That will tell you your external drive's current S.M.A.R.T. status, as well as monitor to see if any new problems crop up.  Another option, for those who are much more advanced is:

OS-X-SAT-SMART-Driver
https://github.com/kasbert/OS-X-SAT-SMART-Driver
https://github.com/RJVB/OS-X-SAT-SMART-Driver/blob/RJVB/SATSMARTDriver-0.5
0.dmg

Discussion.

There was a study released by Google:
http://research.google.com/pubs/papers.html
http://research.google.com/archive/disk_failures.pdf
Failure Trends in a Large Disk Drive Population, which concluded that S.M.A.R.T. wasn't a reliable predictor of drive failure.  (Note: Anecdotal feedback from users to this Web site's author indicates that Volitan's SMART Utility's proprietary algorithm does give a reliable prediction of hard drive failure.)

More information on S.M.A.R.T. technology:
http://www.ariolic.com/activesmart/smart-technology.html
http://support.apple.com/kb/TA27350
http://www.storagereview.com/guide2000/ref/hdd/perf/qual/featuresSMART.html
http://en.wikipedia.org/wiki/Self-Monitoring%2C_Analysis_and_Reporting_
Technology 

Return to Table Of Contents

Moving things to a location other than on your desktop is an easy and free way to pick up better performance. Users have noticed that reducing the number of items on their Mac’s desktop can noticeably increase the performance of certain activities in OS X. This is easy to do. You can even create one folder on your desktop and put everything on your desktop in it. That will do the trick. Nested items within folders on the Desktop don't count. It is only the total number of items directly on your desktop that matter.
http://hints.macworld.com/article.php?story=20051117154624368

http://www.macworld.com/2006/03/features/speedtoptips/index.php

http://reviews.cnet.com/8301-13727_7-10328587-263.html?tag=mfiredir

Another way to go is to put all of the items that would normally reside on your desktop, that you want to be able to access quickly, in a folder; park that folder somewhere other than on your desktop, and then drag that folder to your Dock so that it is always available from the Dock. Whenever you click and hold (or Control-click, or right-click on a two button mouse) on that folder in the Dock, you will be presented with a menu of everything in that folder to choose from. Sort of like the old classic Apple Menu.

Discussion.

Things that you put on your desktop don't really reside there. They actually reside in a folder in your user account. The Desktop folder can be found at:
[hard drive icon]/Users/[your user name]/Desktop
otherwise known as: ~/Desktop, or your "user desktop folder".
Open this folder and you will find everything that you see on your desktop!  Making the stuff that appears in this folder appear on your desktop is resource intensive, and the more things in this folder, the more resources are impacted.

Update:  The need to clear your destop has become controversial.  Some folks claim that Apple has completely changed the way that things are represented on your desktop and that it no longer matters how many items are on your desktop. Others say that they still see a slowdown from having too many items on their desktop, and that clearing their desktop resolves the problem.  it's hard to tell which is the truth, because no one has explained what the changes are, exactly, and Apple has no technical briefs saying that a change was made.  From anecdotal evidence, I think that the situation is somewhere inbetween.  I think that there is still some overhead required to put all of the icons on your destop, but that the performance hit isn't nearly what it once was.

Fortunately, you can quickly and easily prove or disprove this for yourself.  If your desktop is full of icons, drag everything into a folder and see if performance increases afterwards.  If it doesn't, you can simply drag everything out of the folder and back onto the desktop.

Return to Table Of Contents

If you are using Safari as your Web browser, and it starts performing poorly (which isn't uncommon), and none of the other things on this page help, do this:

In Safari:
-Safari menu --> Reset
- Leave everything checked except for:
- Remove saved names and passwords
- Remove other autofill from text

As of OS X 10.10 (Yosemite), Safari no longer has a reset function.  In the Safari menu there is the menu item "Clear history and website data," but unfortunately it is not as comprehensive as a full reset.

Return to Table Of Contents

The first thing that you should do if you have a stability or speed problem with your Web browser is update Flash Player.  It almost always helps.

Uninstall the copy of Flash Player that you have installed with this uninstaller (Adobe recommends doing this first):
http://fpdownload.macromedia.com/get/flashplayer/current/uninstall_flash_player_
osx.dmg

Then download the latest version of Flash Player directly from Adobe, and install it:
http://get.adobe.com/flashplayer/

When you are done doing that, if you haven't done this previously, this will really help your browser's performance: Delete all of your Flash cookies. (Note: This cannot be accomplished using Safari's Security settings.  While they can deal with ordinary cookies, they don't effect Flash cookies).

In addition to the regular cookies that most users know about (and which are perfectly safe and legitimate, despite the mythology surrounding them), there are Flash cookies, which are rarely legitimate. Most web browser's built-in security features don't block and can't purge Flash cookies.  See:

http://www.orzeszek.org/blog/2009/08/12/how-to-delete-flash-cookies-conveniently/

http://www.wired.com/epicenter/2009/08/you-deleted-your-cookies-think-again/

When these cookies accumulate (and they do so very quickly), your Web browser will slow down.  They are easy to get rid of, and at the same time you can make sure that they can't be downloaded to your Macintosh ever again.

Go into System Preferences --> Flash Player --> Storage --> click on the "Delete All" button -->  enable "Block All Sites From Storing Information On This Computer"

The only thing that I've ever encountered that is negatively impacted by deleting and blocking Flash cookies is Pandora, which will still work, but it won't save your user created "channels."  You can set Flash Player to create an exception for Pandora (or any other applications that you approve), but personally I just switched to Spotify instead, which doesn't use Flash cookies.

One last thing that tends to really improve things when your Web browser isn't performing well, is to delete this file:

- Close all browsers.
- In the Finder (that is, with your desktop showing and no applications running)
- Option-click the Go menu
- Your ~/Library will appear in the menu; choose it
- find the  Preferences folder and open it
- delete this file (it will be rebuilt the next time that you launch your Web browser):
com.apple.quicktime.plugin.preferences.plist

Return to Table Of Contents

Ever since OS X 10.4, all archived messages in Apple’s Mail program have been kept in individual Finder-readable files. There are no archived messages in Mail's database.

This is a good thing.  Some other e-mail programs, notably Microsoft’s Entourage, store all of your messages in one big monolithic database.  If the database in a program with a monolithic database becomes corrupted and unrepairable, you can lose all of your archived mail.

Mail works by storing information such as senders, recipients, subjects, etc. in a SQLite database. Mail’s performance can lag, and it can become less stable, as you store more and more archived messages in it.

Periodically deleting old, unwanted e-mail messages, and rebuilding Mail’s database, will usually give Mail a very noticeable performance boost, and help ensure continued trouble-free operation.

Since there are no archived e-mail messages stored in Mail’s database, it is quite safe to rebuild Mail’s database, because if something goes wrong with the rebuild, you can just start over, having lost nothing.

Every now and then (or, ideally, routinely as you use Mail) you should go through all of your mailboxes in Mail and delete all of the messages you no longer wish to keep. Then, in Mail, choose:
Mailbox menu --> Erase Deleted Messages --> In All Accounts
to purge all deleted messages.

After doing this, quit Mail.

Now you are going to rebuild Mail's envelope database.  You can do this manually, via a script, or using the Terminal (your choice, based on how advanced a user you are):

http://support.apple.com/kb/PH14876

http://brettterpstra.com/2012/09/15/vacuuming-your-mail-app-index-still-works-
wonders/

http://www.fixkb.com/2013/03/apple-mail-application-very-slow-to-respond.html

Return to Table Of Contents