(Real applications are usually optimized to best utilize cache, synthetic memory benchmarks are written to effectively disable cache.) If you need the RAM, it will be far faster to fill all the slots and deal with the theoretical slightly slower speeds - rather than paging and other disk I/O to deal with the memory shortfall. If you add a third pair of additional DIMMs, install them on the bottom memory card in DIMM slots 3 and 4. Lay your Mac Pro down on a soft, clean cloth on the desk or work surface to avoid scratching the work surface or your Mac Pro. Reinstall each memory card, pushing it straight down until it's seated in the memory slot.

Silver Tower Mac Pro Q&A - Updated May 22, 2013

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How do you upgrade the RAM in the 'Mid-2010' and 'Mid-2012' (Nehalem/Westmere) Mac Pro models? What type of RAM do these models use? How much RAM do they actually support? Are these models backwards compatible with earlier Mac Pro RAM?

Please note that this Q&A explains how to upgrade the RAM in the 'Mid-2010' and 'Mid-2012' Mac Pro models (model identifier MacPro5,1).

EveryMac.com also provides RAM upgrade instructions for earlier Mac Pro models -- the original Mac Pro (MacPro1,1 and MacPro2,1), 'Early 2008' (MacPro3,1), and 'Early 2009' (MacPro4,1) systems.

Just as it is forallearlier Mac Pro lines, upgrading the memory in the 'Mid-2010' and 'Mid-2012' (Nehalem/Westmere) Mac Pro models is a quick-and-easy procedure. However, it is critical that memory meet certain standards and be installed in a certain way to function properly. These systems also can use more RAM than is officially supported, too.

Photo Credit: Apple, Inc. (Mac Pro)

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Identification Help

If you're not sure if you have an 'Mid-2010' or 'Mid-2012' Mac Pro or an earlier model, the A1289Model Number is insufficient as this identifier is shared by the previous 'Early 2009' Mac Pro models, as well.

However, for the purposes of upgrading the RAM, the 'Mid-2010' and 'Mid-2012' Mac Pro models can be identified collectively by the Model Identifier in software and uniquely externally by EMC Number. More details about specific identifiers are provided in EveryMac.com's exhaustive Mac Identification section.

To locate the model identifier, select 'About This Mac' under the Apple Menu on your computer and click the 'More Info...' button. If the Mac Pro is running OS X 'Lion' (10.7) or later, click the 'System Report' button after clicking 'More Info...' as well. Regardless of the release date or the number of processor cores, all 'Mid-2010' and 'Mid-2012' Mac Pro models share model identifier MacPro5,1.

The EMC number is located on the rear of the system in small type. As carefully hand documented by EveryMac.com, the 'Mid-2010' Mac Pro models share EMC number 2314-2 and the 'Mid-2012' Mac Pro models share EMC number 2629.

These identifiers are easiest to visualize as a chart:

EveryMac.com's Ultimate Mac Lookup feature -- as well as the EveryMac app -- also can identify these models by their Serial Numbers.

Official RAM Type & Unofficial Compatibility & Performance Details

In the PDF instruction manual, Apple specifies that all UDIMMs for the 'Mid-2010' and 'Mid-2012' Mac Pro models must meet these specifications:

• PC3-10600E, 1333 MHz, DDR3 SDRAM UDIMMs
• Error-correcting code (ECC)
• 72-bit wide, 240-pin ECC modules
• 36 ICs maximum per ECC UDIMM

Apple also notes that 'although the memory speed of the UDIMMS is 1333 MHz, they will operate at 1066 MHz or 1333 MHz depending on the processor in the computer.'

More formally, the 'Mid-2010' and 'Mid-2012' Quad Core and Eight Core models are intended to use 1066 MHz DDR3 ECC SDRAM (PC3-8500) modules and the Six Core and Twelve Core models are intended to use 1333 MHz DDR3 ECC SDRAM (PC3-10600) modules. However, all of these models do work with 1066 MHz DDR3 ECC SDRAM (PC3-8500) modules.

Interestingly, in real-world testing, the respected MacPerformanceGuide actually found no difference in real-world performance in a system intended to use 1333 MHz PC3-10600 modules even if the slower 1066 MHz PC3-8500 modules were installed.

Nevertheless, Apple presumably is erring on the side of caution as 1333 MHz memory is designed to work in models that support the slower 1066 MHz memory, but not vice versa. Although many readers have reported that memory from the previous 'Early 2009' Mac Pro models works without issue, Apple formally states that 'DIMMs from older Mac computers cannot be used in your [Mid-2010 or Mid-2012] Mac Pro,' The company also specifies:

When purchasing DIMMs for use in Mac computers, make sure that the memory vendor conforms to the Joint Electron Device Engineering Council (JEDEC) specification. Check with your memory vendor to ensure that the DIMMs support the correct timing modes and that the Serial Presence Detect (SPD) feature has been programmed properly, as described in the JEDEC specification.

In other words, the 'Mid-2010' and 'Mid-2012' Mac Pro models, and Macs in general, can be picky about memory and it is important to purchase from a vendor that has tested their memory in a particular Mac model to ensure compatibility.

Actual Maximum RAM

Although 'Mid-2010' and 'Mid-2012' Mac Pro systems with a single processor, which EveryMac.com notes as the 'Quad Core' and 'Six Core' models, officially support a maximum of 16 GB of RAM, as discovered by site sponsor Other World Computing, they actually can support more. OWC first noted an actual maximum of 32 GB of RAM and later increased this actual maximum to 48 GB of RAM.

Systems with dual processors, which EveryMac.com notes as the 'Eight Core' and 'Twelve Core' models, likewise officially support 32 GB of RAM, but again, OWC found they actually can support more. OWC first confirmed an actual maximum of 64 GB of RAM running Mac OS X 10.5 'Leopard' and later increased this maximum to 96 GB of RAM running Mac OS X 10.6 'Snow Leopard' or higher. More recently, OWC yet again discovered these dual processor models can support up to 128 GB, but only when running a 64-bit version of Windows XP or later or Linux. Mac OS X only can support 96 GB of RAM.

RAM Upgrade Instructions

Apple covers installing memory in the 'Mid-2010' Mac Pro models on pages 43-60 of the PDF User's Guide -- complete with drawings -- and this absolutely should be reviewed before upgrading the memory (Apple did not release a new User's Guide for the 'Mid-2012' Mac Pro models, but the procedure is the same for the 'Mid-2010' and 'Mid-2012' models alike). Just like the 'Early 2009' models, note that installing RAM in groups of three will provide maximum performance in these later systems, too.

Perhaps even better than the official drawings, however, OWC provides a step-by-step video of the upgrade process:

From watching the above video, it is clear that upgrading the RAM in the 'Mid-2010' and 'Mid-2012' Mac Pro is straightforward. However, if you do not feel comfortable -- or have the time -- to upgrade the RAM yourself, professional installation always is a good idea.

Mac Pro RAM Purchase & Professional Installation Options

As noted earlier, just because RAM meets the minimum listed criteria does not mean that it will necessarily function properly, or even at all, in your Mac. Be sure to buy from a quality vendor that has tested their RAM with each Mac model to ensure complete compatibility.

In the US (and many other countries), site sponsor Other World Computing sells memory compatible with each Mac Pro model as well as all other Macs.

In the UK and Ireland, site sponsor Flexx sells Mac Pro compatible memory with free shipping. The company provides flat rate shipping to France, Germany, and Switzerland and inexpensive shipping for all of Europe, too.

In Canada, site sponsor CanadaRAM sells memory for all Mac Pro models with guaranteed compatibility, fast shipping, and no customs.

In Germany, site sponsor CompuRAM sells quality memory for all Mac Pro models with affordable delivery country-wide and in person pick up and professional installation service available in Munich.

In Australia, site sponsor RamCity sells Mac Pro compatible memory with a lifetime warranty and fast, flat-rate shipping Australia-wide.

In Southeast Asia, site sponsor SimplyMac.sg sells Mac Pro compatible memory with free delivery -- and optional upgrade service -- in Singapore and free shipping to Brunei, Hong Kong, Macau, Malaysia, Myanmar, New Zealand, the Philippines, South Korea, Taiwan, Thailand and Vietnam.

Also see:

• How do you upgrade the RAM in the original Mac Pro? What type of RAM does it use? How much RAM does it actually support?
• How do you upgrade the RAM in the 'Early 2008' (Harpertown/Penryn) Mac Pro? What type of RAM does it use? How much RAM does it actually support? Is it backwards compatible with RAM from the original Mac Pro?
• How do you upgrade the RAM in the 'Early 2009/Nehalem' Mac Pro? What type of RAM does it use? How much RAM does it actually support?

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