Bloomfield/Gainestown. With the exception of a second QPI link for dual CPU configurations, these two chips are identical. Both will work in either SP or DP tylersburg motherboards, though bloomfield will be limited to a single CPU in DP motherboards. Gainestown (Branded Xeon 5500), however will be produced in a wider array of frequencies than Bloomfield (branded core i7 and Xeon 3500)
ECC memory support: There is some miss information about the Nehalem platform not supporting ECC memory. This is both true and false. Bloomfield CPUs with the consumer Core i7 branding have ECC memory support disabled. Bloomsfield CPUs with the Xeon 3500 branding and Gainstown Xeon 5500s have full ECC-support up to DDR3 1333.
Single CPU configuration:
When Apple moved to the PowerPC 970 (G5) they created a revolutionary new northbridge to accompany it called U3. U3 was designed be modular. U3 and U3H were designed for use in dual CPU workstations and servers. It was designed to connect to the K2 southbridge with an optional PCI-X controller between them at 1.6, 3.2, or 4.8 GBps through 8 and 16-bit Hypertransport buses. This allowed Apple to offer its G5s with single or dual CPUs, PCI or PCI-X, with 4 or 8 DIMM slots. The family also consisted of U3L designed for desktops. It was paired with a southbridge called shasta. U3L used a physically smaller motherboard and showed up in both the 1.8ghz single CPU PMG5 and the AGP iMac G5.
What does an old PPC G5 chipset have to do with the next revision of the Mac Pro? Perhaps quite a lot. On the intel platform, there was a divide. Desktops and servers/workstations used slightly different chips, with different sockets, different memory, and different chipsets. These factors have kept the base single CPU MacPro as a very expensive proposition as an entry-level Core 2 PowerMac would have been a completely different beast. With Nehalem/Tylersburg, this is no longer the case. The situation is much the same as G5/U3, same basic CPU core, variations of the same chipset, same socket, same memory. Xeon 3500/5500 and Tylersburg SP/DP are for the most part interchangeable. What this means for configurations is unknown, but the hurdles that have kept the line well over the $2000 mark are potentially solved.
