How do you upgrade the RAM in the "Early 2008" (Harpertown/Penryn) Mac Pro? How much RAM of what type does it support? Is it backwards compatible with RAM from the original Mac Pro?

Just like the original Mac Pro, installing RAM in the "Early 2008" Mac Pro is easy, but it is important that the memory meet exacting standards to function as intended.

Officially, the "Early 2008" Mac Pro requires "800MHz DDR2 ECC fully buffered DIMM (FB-DIMM) memory", but more precisely, the memory must meet these specifications:

• 800 MHz, DDR2, FB-DIMMs
• 72-bit wide, 240-pin modules
• 36 memory ICs maximum per DIMM
• Error-correcting code (ECC)

However, the always excellent BareFeats also discovered that the "Early 2008" Mac Pro is capable of using 667 MHz FB-DIMMs that are compatible with the original Mac Pro, albeit at a "maximum penalty of 4% in speed".

Apple also reports that "DIMMs must be installed in matched pairs". There are eight FB-DIMM slots in total on two "riser cards" (four slots per card) that can hold 32 GB of RAM.

Detailed information is printed on the inside of the door of the Mac Pro, and Apple provides a PDF version with photos that absolutely should be read before upgrading the RAM, but perhaps even better, site sponsor Other World Computing has provided a step-by-step video of the process:

In addition to helpful installation videos, as you would expect, Other World Computing also has quality memory that is guaranteed to work with the "Early 2008" Mac Pro and that is quite affordable as well.