Buying RAM

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This guide is meant to provide information about places to buy RAM for your Mac.

For installing your newly bought RAM see the Installing RAM guide.

Then complete your journey by testing your new RAM, following the Testing RAM guide.


Basic information about RAM

Example memory info in System Profiler
Example memory info in System Profiler

Before you purchase memory, you need to know what kind to get. To figure this out, you should search/ask at MacRumors forums. You could check in the manual that came with your Mac as well, but keep in mind that Apple does not specify the best possible specifications of memory upgrade. There will be a section on memory upgrades, telling you what memory will perform the best. Warning: your listed bus speed is not always the same as your RAM speed.

Key things to know:

  • Type: here you will see any number of acronyms, including DDR, DDR2, DDR3, FB-DIMM, and more. You cannot substitute one type for another.

DDR memory is not backwards compatible: you cannot substitute DDR with DDR2/DDR3, or DDR2 with DDR3.
There's also ECC (error correcting RAM), which could be installed in recent Mac Pros.

  • Speed: could be expressed in MHz, or as PCX-Y number - where X stands for a DDR version number, and Y for a maximum data transfer rate (MB/s)
Speed (MHz) DDR3-800 DDR3-1066 DDR3-1333 DDR3-1600 DDR3-1866 DDR3-2133
PCX-Y PC3-6400 PC3-8500 PC3-10600 PC3-12800 PC3-14900 PC3-17000
  • Format: You will usually see DIMM (desktop full sized modules) and SO-DIMM ('notebook' size modules). Each format is divided to subformats by a number of pins.
  • Pins: Different physical sizes of memory chips usually have different numbers of pins. Common numbers for current machines are 204 pins and 240 pins.

Macbook Pro and iMac are using 204-pin SO-DIMM.

  • Size: Different memory modules could accomodate different volumes of information.

CAS Latency requirements

This is very important! If you will install the memory with an unsupported CAS Latency in your Mac, it will not boot up at all or work unstable (constant kernel panics)

Before choosing a memory upgrade, you should find out the CAS Latency of Apple stock RAM which came with your computer.

To do that, you should follow these steps:

    • Tear down your computer as if you are going to do a memory upgrade (could use Apple instruction)
    • Look at the installed memory's label
    • Write down the model number
    • Assemble your computer in reverse order
    • Google for the specifications of memory with a model number that you wrote down earlier

The clear example of CAS latency problem is a current Macbook Pro generation.

Macbook Pro: classic 2011-2013 models, based on Sandy Bridge and Ivy Bridge CPUs

RAM kits with CL >= 11 or CL <= 7 are known to cause problems (kernel panics). So, only RAM kits with CL8, CL9, CL10 are left.

CL8 kits cannot be seen anywhere. CL10 kits are reported to work good by some users.
But, even if it is true, you should still prefer CL9 kits, because they are faster than CL10 kits.

Timings of CL9 RAM: 9-9-9-X, where X is tRas.
If tRas is not specified (9-9-9), then tRas = 9*3 = 27

The smaller tRas is, the faster RAM is.

Dual/Triple channels and maximum amount of RAM

Basic information

Dual-channel: RAM must be installed in matched pairs, pairs need not match other installed pairs.

Triple-channel: Pairing not required however the triple channel architecture means data bus bandwidth will be optimized if RAM is installed in multiples of three.
Installing just two modules will underutilize the bandwidth and if four modules are installed, two modules will be forced to share one of the 3 channels, slightly penalizing throughput.

To find out the maximum supported amount of RAM, follow these steps:

    • Go to "Apple" official website ---> "Mac" ---> Click your Mac image ---> "Tech specs"
    • Scroll about two screens down and copy the model number of your Mac
    • Paste it to Google and find the advanced technical specifications of your Mac model
    • Copy the model number of CPU (processor) and go to the Intel website
    • Find the technical specifications of CPU and check the maximum supported amount of RAM

Mac Pro

Mac Pro 2008 "Penryn" and "Harpertown" 2009 / 2010 "Nehalem" and "Westmere" 2011 / 2012 "Westmere"
Quad-core Octo-core Six-core Twelve-core
Number of slots 8 4 8 4 8
Type of channel Dual Triple Triple
Maximum size of a memory module 4GB 16GB 16GB
Total maximum size of RAM 32GB 64GB 128GB 64GB 128GB

Which RAM to Buy

Macbook Pro

RAM support in classic Macbook Pro models, based on Sandy Bridge and Ivy Bridge CPUs
Screen size Early 2011 Late 2011 Mid 2012
13" 2410M/2620M 2435M/2640M 3210M/3520M
15" 2635QM/2720QM/2820QM 2675QM/2760QM/2860QM 3615QM/3720QM/3820QM
17" 2720QM/2820QM 2760QM/2860QM --------------------


  • Bold CPU models support up to 1600MHz and 32GB RAM
  • Other CPU models support up to 1333MHz and 16GB RAM

8GB (2x4GB) 1600MHz CL9 RAM comparison
Model Works tRas Voltage Price in $
Kingston HyperX LoVo KHX16LS9P1K2/8 YES 27 1.35/1.5 70
Corsair Vengeance CMSX8GX3M2A1600C9 YES 24 1.5 57
Kingston HyperX KHX1600C9S3P1K2/8G YES 27 1.5 61
G.Skill F3-12800CL9D-8GBSQ YES 28 1.5 50
G.Skill F3-12800CL9D-8GBSK YES 28 1.5 60
AData XPG AXDS1600GC4G9-2 NO 24 1.35/1.5 65
Kingston HyperX KHX1600C9S3K2/8GX NO 27 1.5 55

16GB (2x8GB) 1600MHz CL9 RAM comparison
Model Works tRas Voltage Price in $
Kingston HyperX LoVo KHX16LS9P1K2/16 YES 27 1.35/1.5 129
Kingston HyperX KHX16S9P1K2/16 YES 27 1.5 127


  • The smaller tRas is, the faster RAM is.
  • Things marked in bold are good things, things marked in italic are bad things.
  • Some RAM does not work in MBP at 1600MHz - only at 1333MHz, because of XMP (eXtreme Memory Profiles).

I have removed the heat spreader column: now, to reduce manufacturing costs,
some companies are using confusing stickers which look like a real heat spreader.


iMac table: maximum possible speed of RAM inside iMacs from different generations, and recommendations.

These tables should be identical to Macbook Pro tables,
for iMac 2011-2013 models which are based on Sandy Bridge and Ivy Bridge CPUs.

Mac Mini

Mac Mini tables: maximum possible speed of RAM inside Mac Mini from different generations, and recommendations.

These tables should be identical to Macbook Pro tables,
for Mac Mini 2011-2013 models which are based on Sandy Bridge and Ivy Bridge CPUs.

Mac Pro

Mac Pro table: maximum possible speed of RAM inside Mac Pro from different generations, and recommendations.

Left blank until new Mac Pro comes out.

Will it make my machine faster?

Taking your foot off the brake does not make your car go faster - it just discontinues slowing it down. Less reading and writing back and forth to your slow hard drive.

Increasing the memory in the Mac does not increase the Mac's speed - rather it removes slowdowns that result from your programs and data not having enough memory. When there isn't enough memory for all you are doing, operating system is forced to swap memory space on and off the hard drive. Because hard drives are much slower than RAM, this slows the machine down overall.

How much your machine slows down depends on how you are using it. If you use just one program at a time, and don't open large data sets, then you may not notice a speed difference with more RAM.

If you regularly multitask many programs, or use 'hungry' programs:

  • video, audio and photo editing software (Final Cut Pro, Adobe Premier Pro, Photoshop)
  • hardware emulation virtualization software (Parallels, VMWare, VirtualBox)

then you should see noticeable improvement with 8 GB or 16 GB RAM.

When you are running multiple programs at once, more RAM makes switching from one program to another faster,
because operating system can cache the previous program's memory in 'inactive' memory for a longer time before it has to get flushed out to make room.

Specific RAM requirements for PowerPC-based Macs


Mini G4

PC2700 DDR (333 MHz) DIMM, 1 slot, max. 1 Gb (1 x 1 GB) (These machines are very sensitive to out of spec RAM - generic PC DIMMs are not recommended)


Powerbook G4

"Titanium" models (400 MHz - 1 GHz): PC133 SODIMMs, 2 slots, max. 1 GB (2 x 512 MB)

"Aluminum" 12" models (867 MHz - 1.5 GHz): PC2700 DDR (333 MHz) SODIMM, 1 slot, max. 1.25 GB (1 x 1 GB + built in 256)

"Aluminum" 15" and 17" screen models (1.0 GHz - 1.67 GHz pre-October 2005): PC2700 DDR (333 MHz) SODIMM, 2 slots, max. 2 GB (2 x 1 GB)

    • Note: The 1.0 GHz 15" and 17", the 1.25 GHz 15" and the 1.33 GHz 17" require special processor-slewing compatible modules;
    • common PC2700 SODIMMs will not work. Choose a seller who knows the difference and offers RAM that is specifically compatible with your model Powerbook.

"Aluminum" 15" and 17" 1.67 GHz models (HD Screen / DL Superdrive models introduced Oct. 19 2005): PC2-4200 DDR2-533 MHz SODIMMs, 2 slots, max. 2 GB (2 x 1 GB)


PowerMac G3

Blue and White G3 tower, "Yosemite" motherboard 256 MB PC100 DIMMs, requires low density modules, max 1 GB with 4 x 256 MB. These machines will not use 512 MB DIMMs

Beige G3 desktop and mini tower, 256 MB PC66 DIMMs, requires low density modules, max 768 MB with 3 x 256 MB. These machines will not use 512 MB DIMMs. Desktop models require low profile modules.

PowerMac G4

G4 PCI Graphics "Yikes" motherboard 300, 350, 400 MHz: PC100 DIMMs, 4 slots, max 1 GB with 4 x 256 MB low density DIMMs. These machines will not use 512 MB DIMMs

G4 AGP graphics "Sawtooth", Graphite, Gigahertz, Power2Burn and Quicksilver models: PC133 DIMMs 3 or 4 slots, max 1.5 GB with 3 x 512 MB DIMMs.

G4 Mirror Drive Door models: PC2700 DIMMs, 4 slots, max 2 Gb with 4 x 512 MB DIMMs. (It has been reported that 2 x 1 GB DIMMs could be used, but the other 2 sockets then have to be left empty, this is not recommended)

PowerMac G5

Single and Dual-Processor PCI/PCIX bus machines prior to Oct. 19 2005: PC3200 DDR (400 MHz) DIMMs, 4 or 8 slots, max. 4 GB or 8 GB (4 or 8 x 1GB)

Dual-core PCI-e bus machines (introduced Oct 19 2005): PC2-4200 DDR2-533 MHz DIMMs, 4 slots, max. 16 GB (4 x 2GB)


  • Apple's prices for memory upgrade (as well as for hard drives upgrade) are outrageously high.
    Also, RAM sold by Apple is not the fastest possible RAM that is supported by your Mac. Get a Mac with a stock RAM and upgrade later.
  • Apple buys Samsung, Hynix and Micron RAM modules in bulk. There is nothing special about Apple branded memory.
  • Buy RAM only from a large brand - that will greatly reduce the risk of getting faulty RAM, and also you will have a warranty - maybe even lifetime!
  • Always test RAM immediately after purchase - branded RAM could be faulty as well.
  • Buy RAM only from established and reputable sellers. Scammers could sell you a faulty RAM and refuse to make a refund.
    If you are going to buy at eBay, avoid sellers with a small rating or a short history: they could be scammers!

International purchases

When purchasing from outside your country, while the seller may advertise "no taxes or extra charges" you are almost certainly going to be charged for some or all of: VAT/GST/local tax, duties, customs brokerage fees, and/or advancement fees when the package arrives in your country. UPS Ground courier is notorious for charging low shipping costs but sky-high brokerage costs. These fees can substantially increase the cost of your purchase. Air freight is expensive, but often includes the customs brokerage, so it may be a wash against the cost of ground + brokerage. The least expensive way to import goods is through normal postal parcel mail. Unfortunately, that is also the method that is most prone to loss or theft. Always insist on a shipping method that includes insurance and a tracking number. In addition, if there is any warranty issue with your internationally purchased RAM, you can expect to pay shipping costs and customs clearing costs both ways, which can be expensive.

After purchase

Move on to Installing RAM and then Testing RAM. Enjoy!