Thursday, September 06, 2007

Which Intel CPU for a power workstation ?

Xeon processors have been the choice for the ultimate performance server and workstation for some time, however with so many different Intel CPU's available which is the best to get now and planning for the future?

Single and dual quad core Xeon processors are very good for multi threading processes, however on non multithreaded applications this advantage is lost and its just down to raw Ghz speed.

Intel started shipping its new Woodcrest CPUs in June 07 and they are now available from Dell and HP. The key importance with these new processors is that they have upport for a 1,333MHz FSB frequency, up from a previous maximum of 1,066MHz. In theory, this represents a substantial 25% increase in bandwidth between the CPU and the rest of the system, which in particular should help memory performance with DDR3 RAM.

There are 2 types of new processor releases of interest:
Intel® Core™2 Extreme quad-core processor QX6850
Quad-Core Intel® Xeon® processor 5300 series

A usefull list of the CPU's Dell ship is here
So should you choose a Core 2 Extreme or a Xeon? The answer is difficult to call and I'm still gathering information on this

The fastest Xeon quad cpu runs at 2.66ghz and I think a single quad of this type would be better than a dual quad of 1.8ghz with a 1066mhz fsb.

The fastest new release is at the very top end of Intel's enthusiast CPU line-up: the Core 2 Extreme Edition QX6850, replacing the QX6800 is not a Xeon! It is a quad-core processor and is the third Core 2 Extreme model to be released since the original quad-core QX6700 at the end of last year. The new part's basic specifications haven't leapt massively, starting from 2.66GHz in the QX6700 and now hitting the 3GHz mark. The architecture remains identical, with two dual-core dies in one package, each with 4MB of L2 cache, making for a total of 8MB.

Also the QX6850 - like all other Extreme Edition Intel CPUs before it - is clock unlocked, allowing for direct clock-multiplier overclocking. This means that Dell is shipping a 3.4Ghz XPS machine using the 3.0Ghz QX6850.

The last fly in the ointment is the new DDR3 memory.

DDR2 RAM is set to be replaced by DDR3. DDR3 offers benefits; operating voltage is reduced from DDR2's 1.8V to 1.5V, and while DDR2 officially supports a maximum I/O bus rate of 533MHz, DDR3 goes up to 800MHz - effectively 1,600MHz due to DDR's double-pumped bus. The pre-fetch buffer is also doubled, from 4 bits to a whole byte.
These improvements are now offset by increased CAS latency, though. Most DDR2 DIMMs have a latency of 4 or 5 clocks before they can start to return the data stored at a given address. Current DDR3 modules, meanwhile, have a latency of 7-9 clock cycles, and while this may fall as the manufacturing process is refined, the standard dictates an absolute minimum CAS latency of 5 clock cycles for DDR3.
So the answer is not clear and information gathering is still ongoing, but hopefully this article has identified the main issues.

Going int the future, Intel are working on a Penryn-microarchitecture parts to be released towards the end of the year. Penryn-based processors will be the first produced with a 45nm fabrication process; the existing CPUs remain on 65nm

(Extracts from PcPro article)

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