The Mac includes a handy utility you can use to monitor memory performance and determine whether you need additional RAM. You can use Activity Monitor to discover how you currently use the RAM installed on your Mac and to see if additional memory would be helpful.

2009 Mac Pro Memory Specification

The 2009 Mac Pro was the first to dispense with the FB-DIMMS (Fully Buffered Dual In-Line Memory Modules) and heat sinks, which were used in the first few years of Intel-based Mac Pros. The 2009 Mac Pro uses the following type of RAM instead:

PC3-8500, 1066 MHz, DDR3 ECC SDRAM UDIMMS

So, what does that all mean?

PC3-8500 is the module name, which describes the peak transfer rate obtained from the memory module. In this case, 8,500 MB/s. 1066 MHz is the clock speed. DDR3 stands for double data rate type three, a high-speed RAM interface. EEC is error-correcting RAM, which can detect and correct errors when the processor reads the RAM’s data. SDRAM is synchronous dynamic random access memory. In essence, the RAM and the processor memory bus are synchronized to the same clocking system. UDIMMS means the memory is unbuffered, unlike the FB-DIMMS mentioned earlier.

2012 and 2010 Mac Pro Memory Specifications

The 2012 and 2010 Mac Pros used two speed ratings of RAM, depending on which processor type was installed.

Quad-core and 8-core models used PC3-8500, 1066 MHz, DDR3 ECC SDRAM UDIMMS—the same RAM used in the 2009 Mac Pro.6-core and 12-core models used PC3-10600, 1333 MHz, DDR3 ECC SDRAM UDIMMS. This RAM had a faster clock speed to match the faster memory controller in the 6-core and 12-core processors.

It’s possible to use the slower PC3-8500 memory in 6-core and 12-core Mac Pros. The processor’s memory controllers can slow down the clock rate to match the slower RAM. However, you’ll receive the best performance if you correctly match the faster processors with the faster RAM. If you upgraded one or more processors from a quad-core to a 6-core, you currently have the slower RAM installed. You may continue to use the slower RAM, but you’ll get the most out of the processor if you upgrade to faster RAM.

Installing RAM in 2012, 2010, and 2009 Mac Pros

When it comes to RAM, the 2012, 2010, and 2009 Mac Pros are similar. The memory slot layout and how the slots connect to the processor’s memory channels are the same. The main difference when installing RAM is the processor. The single-processor models have a processor tray with a single large heat sink and one set of four memory slots. Dual-processor models have a processor tray with two large heat sinks and eight memory slots. The eight memory slots are grouped in sets of four; each group is next to its processor. Not all memory slots are created equal. The processors in the Mac Pro each contain three memory channels, which are wired to their memory slots in the following configuration. Single-processor model:

Slot 1: Memory Channel 1Slot 2: Memory Channel 2Slots 3 and 4: Memory Channel 3

Dual-processor model:

Slot 1: Memory Channel 1, Processor 1Slot 2: Memory Channel 2, Processor 1Slots 3 and 4: Memory Channel 3, Processor 1Slot 5: Memory Channel 1, Processor 2Slot 6: Memory Channel 2, Processor 2Slots 7 and 8: Memory Channel 3, Processor 2

Slots 3 and 4, as well as slots 7 and 8, share a memory channel. The best memory performance is achieved when slot 4 (single-processor model) or slots 4 and 8 (dual-processor model) are not occupied. By not populating the second of the paired memory slots, each memory module can connect to its dedicated memory channel. If you populate the last memory slots, you may reduce optimum memory performance, but only when the memory in the shared slots is accessed.

Memory Limitations

Officially, Apple says the 2012, 2010, and 2009 Mac Pros support 16 GB of RAM in the quad-core models and 32 GB of RAM in the 8-core versions. This official support is based on the size of the RAM modules that were available when the 2009 Mac Pro first went on sale. With currently available module sizes, you can install up to 48 GB of RAM in the quad-core model and up to 96 GB of RAM in the 8-core version. Memory modules for the Mac Pro are available in 2 GB, 4 GB, 8GB, and 16 GB sizes. If you choose the 16 GB modules, you can only populate the first three memory slots. You cannot mix modules of different sizes; if you choose to use 16 GB modules, these must all be 16 GB. Preferred memory slot population for a single-processor Mac Pro:

Two memory modules: Slots 1 and 2.Three memory modules: Slots 1, 2, and 3.Four memory modules: Slots 1, 2, 3, and 4.

Preferred memory slot population for a dual-processor Mac Pro

Two memory modules: Slots 1 and 2.Three memory modules: Slots 1, 2, and 3.Four memory modules: Slots 1, 2, 5, and 6.Six memory modules: Slots 1, 2, 3, 5, 6, and 7.Eight memory modules: Slots 1, 2, 3, 4, 5, 6, 7, and 8.

In the above configurations, slots 4 and 8 are the last to be populated, ensuring the best overall memory performance.

Memory Upgrade Instructions

The following manuals contain memory upgrade instructions. Choose the one for your Mac Pro.

Apple 2012 Mac Pro Manual, including memory upgrade guide. Apple 2010 Mac Pro Manual, including memory upgrade guide. Apple 2009 Mac Pro Manual, including memory upgrade guide.

Memory Sources

Memory for Mac Pros is available from many third-party sources. The ones listed here are reliable and represent a few of the available choices. These are listed in alphabetical order, not preferential.

Crucial Other World Computing Ramjet Transintl.com