(Revised June 16, 2008) Yesterday, Apple announced its next version of OS X, but it did it so quietly that the announcement seemed more like compensation for a mistake (a premature press release from Apple Canada) than a planned event. The new version, named Snow Leopard, is intended to improve performance and stability rather than introduce lots of new features. However, a new feature appears to be "priming the pump" for some major new hardware announcements at Apple's 2009 Worldwide Developers' Conference next June.
It's called "Grand Central," and it appears to be a rewrite of those portions of OS X that aren't multiprocessor- (or multicore-) aware. The issue is that we've gone about as far as we can go with increasing clock speeds in order to get better performance, so the approach favored by Intel, AMD and just about everyone else is to add more cores to each processor. However, unless the software is designed to take advantage of multiple processors/cores, you don't get any performance advantage. Even in those cases where the software is fully multithreaded or multiprocessor-aware, the performance doesn't scale linearly as more processors are added; typically, the second processor or core only improves performance by 80%, and adding more processors results in even smaller incremental gains.
Apple claims that Grand Central will make all of OS X fully multiprocessor-aware (in essence, fully multithreaded,) and it will also make it significantly easier for application developers to write fully multithreaded software. Intel's Nehalem family of processors is scheduled to be released in Q4 2008, starting with four-core/eight-thread models for servers and high-end desktops. The performance kick from Nehalem over Intel's current Penryn generation of processors is expected to be big--approximately 20-30% overall, but closer to 70-80% for multithreaded applications.
I expect to see a dramatically refreshed, or possibly even completely redesigned Mac Pro at or prior to the Worldwide Developers' Conference next June, released concurrently with Snow Leopard. Apple should be able to stay with its existing two-processor/eight-core designs, but get big performance boosts at lower power consumption with Nehalem. At this point, unless you need to get a Mac Pro in the six months, you're probably wise to wait until next June for a Nehalem-based system. Snow Leopard will provide significant performance advantages even on current-generation systems, but it will need Nehalem in order to take full advantage of what it will be able to do