What are the differences between the "Early 2009/Nehalem" Mac Pro models?

There are significant differences between the "Early 2009/Nehalem" Mac Pro models -- the Mac Pro "Quad Core" 2.66 (2009/Nehalem) and Mac Pro "Eight Core" 2.26 (2009/Nehalem).

Externally, the "Early 2009/Nehalem" Mac Pro models are the same and share connectivity as well -- with dual video ports (one Mini DisplayPort and one dual-link DVI port), 5 USB 2.0 ports, 4 Firewire "800" ports, dual Gigabit Ethernet ports, and optical digital audio Toslink in/out and analog stereo in/out. Bluetooth 2.1+EDR is standard but AirPort (802.11a/b/g/n) is an optional upgrade.

The "Early 2009/Nehalem" Mac Pro models are powered by a 45-nm Xeon "Nehalem Quad Core" processor or processors, which have a dedicated 256k level 2 cache for each core and 8 MB of "fully shared" level 3 cache for each processor. The 64-bit "Nehalem" architecture boasts numerous improvements compared to earlier systems and supports "Hyper-Threading" -- which "allows two threads to run simultaneously on each core" and "Turbo Boost" -- which "automatically boosts the processor speed based on workload" (so if an application is only using one core it will automatically increase the speed of the core in use and turn off the unused cores).

Additionally, and perhaps most remarkably, "Nehalem" introduces a new "QuickPath Interconnect" (QPI) system described as a "bidrectional, point-to-point connection" that provides "quick access to the disk, I/O, and other Mac Pro subsystems".

Photo Credit: Apple, Inc.

Internal expansion includes four drive bays that support Serial ATA 3Gb/s drives (one occupied by a 640 GB hard drive by default), have two 5.25" optical drive bays (one occupied by an 18X DL "SuperDrive" by default), and have four PCI Express 2.0 expansion slots (two x16 slots and two x4 slots with one x16 slot occupied by a 512 MB NVIDIA GeForce GT 120 graphics card).

Both models have the processor(s) and memory mounted on a "slide out" tray for easy upgrading, however, and this is a critical difference, the "Quad Core" model (MB871LL/A) only has four RAM slots and supports an official maximum of 8 GB of memory (unofficial maximum of 16 GB) whereas the "Eight Core" model (MB535LL/A) has eight RAM slots and supports an official maximum of 32 GB of memory.

All differences between the standard models are summarized below for your convenience:

"Nehalem" Mac Pro	"Quad Core" 2.66	"Eight Core" 2.26
Xeon Processors:	2.66 GHz Quad Core (3500)	2.26 GHz Quad Core (5500) x2
Standard Memory:	3 GB	6 GB
Maximum Memory:	8 GB†	32 GB
Memory Slots:	4	8
Video Card:	NVIDIA GeForce GT 120*	NVIDIA GeForce GT 120*
Video Memory:	512 MB	512 MB
Hard Drive:	640 GB	640 GB
Optical Drive:	18X DL "SuperDrive"	18X DL "SuperDrive"
Price:	US$2499	US$3299

* By custom configuration, both models also are available with as many as four NVIDIA GeForce GT 120 graphics cards (for US$150/each after the first one) or an ATI Radeon HD 4870, also with 512 MB of GDDR3 memory, for an additional US$200.

† The low-end Mac Pro "Quad Core" 2.66 (2009/Nehalem) officially supports 8 GB of RAM but third-parties have been able to upgrade the system to 16 GB of RAM using four 4 GB memory modules.

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Please refer to the Ultimate Mac Comparison feature to dynamically compare any Mac Pro model to any other G3 or later Mac.