Take a look at http://www.theinquirer.net/gb/inquirer/news/2007/10/05/intel-extreme-penryn-shortage Here's an excerpt: However, the high-rpm hummingbirds buzzing around Tokyo told us another reason yesterday, which sounds far more plausible to - Apple loves the Penryn. It covets both the Yorkfield Extreme for its mainstream boxes and Harpertown Xeons for the next Mac Pro. In particular, the massive memory throughput and SSE4 improvements help Mac-type apps shine more - think about an in-memory huge image manipulation task than needs both of these features. So, the rumour says that Apple pretty much pre-booked all the amounts of top Penryn bins that could be booked for this year - especially the X548". This excludes the minimum quantities for other big vendors so that they will be able to claim at least starting to ship their stuff. Those other vendors will, in reality, mostly have to count on the "standard" Penryn speed bins, a notch or two below the top ones.