Other World Computing has begun selling 4GB SDRAM memory modules for the Quad-Core Nehlaem Mac Pros that were introduced in March. A reader emailed OWC and confirmed that 4GB modules had been successfully tested on the Quad-Core Mac Pros.
According to Apple's official specs, the Quad-Core Mac Pros only support up to 2GB modules in its 4 memory slots resulting in a maximum installed memory of only 8GB. This finding by OWC means the maximum installed memory in these new machines is at least 16GB. While the cost of 4GB modules is somewhat prohibitive at the moment, this should ensure future expandability as the price of memory drops.
In contrast, Apple's 8-Core models carry 8 memory slots total and can officially support 4GB modules bringing their maximum installed memory capacity to 32GB. This advertised 8GB max vs 32GB max RAM discrepancy between the Quad and 8-Core machines has been a major issue for some customers. Apple has been known to under-advertise the maximum ram capacities for their machines in the past.