A Quick DRAM Speed Note

RAM Speed Calculation

I see a lot of confusion about this subject so here is a quick guide for finding out what sort of RAM your computer takes. Let’s say you are out at a store, and see what looks like a great deal on some more RAM for your computer, but you don’t know what type to get. To find out what memory “PC#-XXXX{X}” your computer needs but you don’t have a manual handy, do the following:

If you know your data rate (1066 or more commonly 1333 these days) multiply it by 8 and round to the nearest hundred (but most manufacturers round down) and you can figure out what goes in the XXXX{X}. A data rate of 1333 * 8 = 10664 or “10600,” the “#” is for the data rate type. So  PC3-10600 (SO-204pin) is what 2011 MacBook Pros take. It is DDR3  1333 Memory.

My MacBook Pro (2009: 5,5) takes DDR3 – 1066. Using a quick bit o’ Math, that translates to PC3-8500

Macs Are Easy

If you happen to have your computer handy and you are on a Mac, you can also open the System Information Application located in

Applications/Utility/System Information (System Profiler in previous OS X releases)>Memory

or

Apple Menu>About This Mac>More Info…>Memory and it will tell you what type of DRAM it takes and how many slots are full.

Where to Buy

Among my favorite Mac hardware resources is Other World Computing because their prices are competitive and they stand behind their products. I had purchased RAM from OWC that ended up being defective. I did not find this out until my new installation of Leopard started crashing under heavy memory loads. (they change how OS X uses memory to use more of it if available, and when I upgraded the memory that was usually not used in 10.4, was activated in 10.5 to speed the system up.) But this discovery took place over a year after I purchased the memory from them. I was hoping “lifetime guaranty” meant what it suggested—a hassle free exchange. It took one phone call, my invoice number and about 10 minutes for them to cross ship a replacement set out to me. It was truly hassle free. Since then they are my first consideration when buying new memory. So, if their prices are within $10–15 of competitors, I go with them.

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