This is a spin off from Mac OS X speed FAQ.
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Special note on Parallel's Desktop build 1898. It will limit your machine to 1.95 GB of RAM. Contact the vendor if you run into this bug on how ot fix it.
Apple had a Repair Extension Program for logicboards with bad RAM slots. When buying RAM, make sure it is to Apple's specifications by model name and release date and if bought third party that it matches those name and release dates, and does not exceed them in amount or specs. Note, 1600MHz LPDDR3 onboard memory may be used by the mid 2013 MacBook Air, but only RAM that is stated by manufacturer to work with the mid 2013 MacBook Air is actually compatible. And run the hardware test CD (Instructions for Intel Mac and PowerPC Macs from restore discs) on your machine if it has one, or the Apple System Profiler in the Applications/Utilities folder of Mac OS X or in the Apple menu of Mac OS 9 to ensure the RAM got properly installed. Apple has an article on reading the Process Viewer, which should help you decide if you need more RAM. Another good article on RAM is at Macworld on how to tell if you need more. The third party website, https://github.com/upekkha/AppleHardwareTest offers another means of getting the hardware test if you know what your machine came with. To figure out what your machine came with, use this tip I authored on Apple's website. Rember is a good RAM test program, and so is the using the latest version of Techtool Pro or Deluxe (see my Safe Utilities FAQ for more info on Techtool Pro and Deluxe). Macs which didn't come with a Hardware Test CD may have also come with a Hardware Test Volume you can boot to see if there is an AppleCare repairable hardware issue, as well as detect really bad RAM. The Hardware Test volume comes in two versions, one bootable by the Startup Manager such as found on the Powerbook G4's restore CDs, whose instructions are valid for any PowerPC Mac with a Hardware Test Volume, and then there are the instructions for Intel Macs. Note though that no hardware test software can detect all bad RAM, but if it is indicated as bad by any test, it should be replaced.
Also depending on the machine you are working on instructions for installing RAM may be found on Apple's Customer Installable Parts page. For those RAM slots that do not have instructions on the Customer Installable Parts page note that any damage that happens to your machine due to your own RAM installation may cause the warranty to be voided. Be particularly careful that no static electricity gets to the motherboard. This means touching the power supply with one hand when the computer is plugged in but turned off. Two hands simultaneously you might risk hurting yourself severely. Use the same hand to touch the RAM and insert it in the slot. Some RAM vendors also have wristbands you can attach via a cable to either the frame of the computer, or to the power to make sure you don't have any static electricity reaching your hand during the operation. Also check whether or not special cooling gels or pads are needed to be replaced after the work (this is true of the dome shaped iMac with the Flat Panel display and its non-user accessible slot). If you have any discomfort with the concept of installing RAM, ask an authorized service technician (link only valid for the United States. For other countries check the Where to buy or support links on Apple's international webpages found through the links at the bottom of its main website) to do the work for you.
The following is from a third party with valuable info:
To protect your newly installed RAM, it is highly recommended that you plug the computer into a surge protector or battery backup device instead of plugging it directly into the wall or into a power strip. Many power strips are not actually surge protectors and won't stop a burst of electricity from harming your computer. When shopping for a surge protector, make sure the packaging says it provides surge protection. Some brands will even come with a warranty covering any plugged in equipment should it be damaged by a surge of electricity.
Author's note: A direct lightning strike can damage even a surge protected computer. It is not to say that you shouldn't protect your computer with a surge protector, just so you don't have any false assurance that it will always protect you. Only a backup for your data ill protect your data that is not plugged in at the time of the lightning strike.
It has been found that exceeding official specs can yield a really bad bug to emerge on notebooks in Apple's Powerbook G3 Developer Note on page 91:
The restriction on sleep current is required not only to maximize the battery life but to meet the limitations of the backup battery during sleep swapping of the main battery. Developers of RAM expansion modules that exceed the limit on sleep current must include a warning to the user that battery sleep swapping may not work with those modules installed. Active 1.2 A (8 devices at 150 mA each) Active 8 mA per bank
Unfortunately not all RAM developers give this warning, so exceeding specs on RAM power could yield an issue.
System requirements for RAM are outlined in the bullet listing below:
If you have the correct amount, you may need replacement RAM these vendors have been rated good by members of forums I've participated in:
Lifetimemory , Macramdirect, Memoryx.net, The Chip Merchant, EDGE Apple Memory, Macsolutions, Kingston (avoid Value RAM, but other versions OK), or TJS Electronics, RAM Jet.
The above statement was true as of the last writing of this portion of the FAQ. If you find they no longer back their RAM, please submit feedback to my guestbook. Note, the RAM in the Flat Panel iMac is only accurately reported by the hardware test CD and not the System Profiler. Even when RAM is to spec, sometimes it can be bad RAM for Mac OS X and at least you should remove any additional RAM the machine had installed to see if you suspect you have a bad RAM module. If the computer boots with a series of beeps (Apple articles on PowerPC and Intel Macs tell you how many beeps for each platform), and won't move further, that usually means the internal RAM test of the boot process detected bad RAM or bad slots on the logic board. Before assuming the RAM is bad, check if deleting the contents of your /var/vm/app_profile folder (the virtual memory files of Mac OS X) fixes your problem. To delete those files, restart the computer holding down the SHIFT key. Then run Onyx to clean the virtual memory swapfile. Restart as instructed. The wrong RAM may yield unpredictable results. One of the most notorious of these symptoms of bad RAM is a kernel panic. System freezes that can't be caused by the size of files being used, and the amount of free hard disk space being available being too low can frequently be the result of bad RAM. These freezes will in Mac OS X give you a spinning beachball that lasts for more than 10 minutes, and a force quit with command-option-escape (where command is the Apple logo key on your Apple keyboard) key combination doesn't bring up the force quit window. If it does bring up the force quit window, attempt to force quit the non-responding program. Data will be lost from that program after the last save. Bad RAM is discussed in more detail here: http://www.macintouch.com/readerreports/badram/index.html.
Apple recently released an interesting developer note on why RAM may no longer work like it used to: Q & A article 1344. Return to Mac OS X Speed FAQ, or Kernel panic FAQ.