The Nocona CPU

The new Xeons are available at speeds of up to 3.6GHz and run on an 800MHz bus, unlike their 533MHz predecessors. The chip still uses the 604-Pin package, but there have been architectural changes. The processor now uses the "Prescott" core with the addition of the EM64T 64-Bit instruction set. Unlike the previous "Northwood" based Xeons, these have 1MB of Level 2 Cache. Our particular chips lacked in Level 3 Cache, although we expect these to be on the road map. Just like the Prescott Pentium 4s, these chips run hot and require a decent level of cooling.

Despite being used in servers for a while now, 64-Bit computing has not really had a huge effect on the workstation market. AMD have had the 64-Bit Opteron ready since April 2003 and Linux distributions to go with them, but for most users, the lack of a 64-Bit Windows OS and 64-Bit drivers has been a great hindrance. As the 64-Bit editions of Windows XP and 2003 Server draw closer and closer to completion, Intel feel now is a good time to enter into competition with the AMD64 platform.

Unlike the Itanium, which is solely a 64-Bit processor, these chips have the ability to run in both 32-Bit and 64-Bit mode. Some devices, such as a large majority of PCI cards cannot directly access memory above the 4GB point. To solve this, the software has to ensure the physical memory address is below the 4GB point. AMD solved this solution by using a hardware IOMMU, which is effectively a "bounce buffer" or look-up table of physically memory addresses corresponding to a virtual address that is given to the incompatible hardware, allowing it to use memory above the 4GB barrier.

Intels solution isn't quite as elegant. If a device needs to access memory above the 4GB point, the data is just copied from wherever it is, to a fixed location below the 4GB point. This takes time and can reduce performance. In extreme cases we have heard there could be as much as 30-50% decrease in performance on the Nocona platform.

AMD decided to double the number of integer registers when in 64-bit mode. Because of this, in some situations there is actually a performance boost to be gained by running in 64-Bit mode. Microsoft are quoting an 8% overall system performance boost, while other reports are suggesting as much as 47% in certain cases. Intel may well offer similar performance boosts, but they certainly haven't been talking about them and Microsoft weren't as convinced either, so until we can test a machine in 64-Bit mode ourselves, we won't know for sure.

Because of all this, we aren't going to know the true performance of either of these 64-Bit solutions until there is a working copy of Windows, and drivers to go with it. We tried installing the current Beta on the Nocona system, but to no avail. It would seem the two chips are not quite 100% compatible. This doesn't look hopeful for applications written for the AMD64 instruction set working with Nocona either. There is a Nocona ready version of Windows XP 64-Bit, but we couldn't get hold of this until it was too late.

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