This model was offered as a custom configuration of the Mac Pro "Quad Core" 2.8 Server (2010/Nehalem). However, this system has significant technical differences and is documented as its own model, accordingly.
The Mac Pro "Six Core" 3.33 Server (Mid-2010/Westmere) features a single 3.33 GHz Six Core 32-nm Xeon W3680 (Westmere) processor with a dedicated 256k of L2 cache for each core and 12MB of "fully shared" L3 cache.
By default, it is configured with 8GB of 1333 MHz DDR3 ECC SDRAM, two 1TB (7200 RPM, 32 MB cache) 3Gb/s Serial ATA hard drives, an 18X dual-layer "SuperDrive" and an ATI Radeon HD 5770 graphics card with 1GB of GDDR5 memory.
Expansion includes two external 5.25" "optical" bays (one available by default), four internal 3.5" "cable-free, direct attach" hard drive bays (three available by default), and four PCIe 2.0 slots (one free PCIe 2.0 x16 slot and two free PCIe 2.0 x4 slots with the default single graphics card installed).
Port selection includes five USB 2.0 ports, four Firewire "800" ports, dual Gigabit Ethernet, two Mini DisplayPorts and a dual-link DVI port, and more. AirPort Extreme (802.11a/b/g/n) and Bluetooth 2.1+EDR comes standard.
In many ways, the Mac Pro Server represents a throwback to the days of the Mac Server G4 series where Apple shipped a server "version" of an otherwise identical Power Mac G4 model, but often configured with more RAM and/or a larger hard drive and always with pre-installed server software.
Likewise, the Mac Pro "Six Core" 3.33 (Server) is identical to the Mac Pro "Six Core" 3.33 (2010/Nehalem), but ships with more RAM and a pre-installed copy of Mac OS X 10.6 Server.