Tukwila - 2 Billion Transistors Of Goodness

The upcoming quad-core Itanium processor, codenamed Tukwila, will herald in a number of firsts. It will not only be the first 2 billion transistor processor, it will also be the first quad-core Itanium processor, as well as the first processor to use the new Intel QuickPath point-to-point processor interconnect. Here are the details.

Core, Cache & Memory

The Tukwila is the first quad-core Itanium processor. With multi-threading support, it can handle up to 8 threads simultaneously. You can see the general chip design in the micrograph on the right.

Like other Itanium processors, it will have a three-tier cache hierarchy - L1, L2 and L3. However, Intel refused to go into the details, like the actual cache sizes. They would only reveal that the total on-die cache would be 30MB.

While that may sound like a lot, it actually means that each Tukwila core has less cache (7.5MB of L2 and L3 cache per core) than the current Itanium processors which boast up to 12MB of L3 cache alone per core.

Of course, cache isn't everything. The Tukwila, after all, has four processing cores. It also uses the new QuickPath Interconnect which would greatly improve processor-to-processor bandwidth.

There will be a total of four full QuickPath links and two half links. When we asked about the reason for this rather odd choice, Justin only replied enigmatically, "We selected this based on our assessment for designing a highly scalable platform with high bandwidth and low latency."

The Tukwila has two integrated QuickPath memory controllers which would support registered DDR3 DIMMs via a buffer chip on board. Each processor will have four DDR3 channels with a peak total bandwidth of 34 GB/s. That would mean the integrated memory controllers only support registered DDR3 up to the PC3-8500 speed grade.

Performance

Thanks to the features above, Intel says it will deliver over twice the performance of the current dual-core Itanium 9100 (Montvale) series of processors.

At launch, which would be in the second half of 2008, Intel will offer at least two different SKUs. The first would be a 2 GHz SKU with a 170W TDP. Although there have been some speculation that the Tukwila is not capable of sustaining 2 GHz on all four cores, Intel asserts that the 170W TDP model is capable of doing so.

The second SKU would have a 130W TDP. It is currently unknown what clock speed this model would run at. However, Intel claims it would offer twice the performance of the dual-core Itanium 9100 series of processors at 25% more power consumption.

Advanced RAS

The Tukwila features improved Soft Error Rate (SER) immunity, thanks to soft error hardened circuits which have been designed for advanced RAS (Reliability, Availability and Serviceability). What this means is the Tukwila will have equivalent "per-socket SER" as the dual-core Itanium 9100 (Montvale) series of processors, even with almost 3X the number of logic circuits.