The Xserve Xeon Nehalem 2.66 "Eight Core" (Early 2009) technically is a "build-to-order" configuration of the Xserve Xeon Nehalem 2.26 "Quad Core" (Early 2009), but also is documented as a separate model for reader convenience. Other than the processors, these two models are identical.

The Xserve Xeon Nehalem 2.66 "Eight Core" (Early 2009) is powered by dual 2.66 GHz Quad Core 45-nm Xeon X5550 (Nehalem) processors with a dedicated 256k of level 2 cache for each core and 8 MB of "fully shared" level 3 cache.

By default, it is configured with 3 GB of 1066 MHz DDR3 ECC SDRAM, a 160 GB (7200 RPM, 8 MB cache) hot-plug "Apple Drive Module" (a 128 GB SSD option -- which does not occupy a drive bay -- was available for an additional US$500), an 8X dual-layer "SuperDrive", and NVIDIA GeForce GT 120 graphics with 256 MB of GDDR3 memory. Ports include Mini DisplayPort (VGA and DVI supported with optional adapters), three USB 2.0 ports, and two Firewire "800" ports.

Compared to the "Early 2008" Xserve replaced, the "Early 2009" Xserve models use a substantially faster architecture that 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). It also replaces the frontside bus with 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 Xserve subsystems". Apple reported that these improvements add up to "twice the performance" of the previous system.

Despite the age of this system, site sponsor Other World Computing has RAM, hard drives, SSDs, and other upgrades available for this specific Mac while supplies last.