Xeon 2.8GHz DP & 2.0GHz MP - Part I: Taking over the Enterprise

Xeon MP - 108 Million Transistors @ 2.0GHz

Just a couple of weeks ago Intel introduced the first 0.13-micron Xeon MP parts. As we mentioned in the introduction, the Xeon MP isn't special for its ability to run in quad processor configurations but rather its massive on-die caches.

The new Xeon MP comes equipped with the same 512KB on-die L2 cache as its DP counterpart, but is also outfitted with a massive 2MB on-die L3 cache. The on-die L3 cache and its associated controller logic increases the Xeon's transistor count by no less than 53 million transistors. The end result is that the Xeon MP has a total of 108 million transistors, that's about twice the size of the Xeon DP.

Socket-603 (Xeon MP)

Getting a 55 million transistor processor to run at 2.80GHz isn't a big deal for Intel, but getting a 108 million transistor CPU to run that fast is considerably harder. As you all know, the more transistors you have on a CPU the larger your die size becomes; and the larger your die, the more defects will be present, thus driving the overall yield (ratio of working chips to total chips produced) down.

Luckily the majority of the transistors on the Xeon MP are used for cache, which is much less prone to showstopping defects thanks to redundancy that's built into the cache (there's actually slightly more cache than necessary on the CPUs, just in case defects do occur in some parts of it). However, in order to make sure that Intel doesn't throw away more Xeon MPs than they sell, they limit the clock speeds on the processors. Remember that it is difficult to get good yields on higher clocked CPUs, so one way of balancing out the large die area of the Xeon MP is to keep clock speeds much lower than the Xeon DP.

The result is that the fastest 0.13-micron Xeon MP ships at 2.0GHz, approximately 30% slower than the fastest Xeon DP. This raises an interesting question that many IT managers will face - what's faster: 2.8GHz processors with no L3 cache or 2.0GHz processors with 2MB L3 caches? We'll be answering that shortly, but now let's take a look at the new chipsets.