Processor Core Communication

A Historical Look At If You Should Buy Intel's Latest Quad Core Processor, Or Wait...

The recent release of quad core processor technology for the personal computing market has muddied the waters once again as to which is the best processor to buy for that shiny new beige box. We sympathize with your confusion, and realize that studying processor design is probably not what most computer users wish to spend serious time on when choosing a new processor. In addition, some of the older processors have been slashed in price and are more affordable.At this point, I think just about everyone would agree that a dual core processor, in general, is preferable to a single core processor. This allows multiple applications to run simultaneously without the system slowdowns that a single core chip will experience. For example, notice how much the system will slow down when running an antivirus scan while trying to surf the web.

However, on the recent quad benchmarks I have reviewed, four cores don’t speed things up on most applications. Looking at their design reveals the reason. Think of this as Multicore Processor Design for Dummies.


I’m going to approach this from a historical perspective. Intel was the first to market with a dual core chip. It’s called the Pentium D processor. Intel managed to squeeze two processors onto one piece of silicon. However, they didn’t redesign the chips, and they didn’t directly communicate. This means that in order for the two chips to communicate, they needed to send the data through the front side bus. This is hardly efficient, and slows things down a bit. We can see from my diagram that the two cores, although on the same chip physically, have no direct connection. This was the first generation of dual core chips; the Pentium D 805 is one popular option and a decent performer for a budget box. However, the true potential of a dual core processor was just starting to be realized.

The next step up is to allow the cores to communicate directly. AMD designed this into their Athlon X2 series and called it a “crossbar.” This simple little bridge allows the cores to share data from core to core directly. When one is overloaded, and the other idle, they can split the workload more evenly. Intel’s Core 2 Duo series of chips also uses a similar technology. These are currently the fastest dual core chips on the market, and are great performers.

Now, here comes the monkey wrench. Once again, Intel wants to be the first to market with a new technology, and this time it’s quad core processors. Rather than start with a blank piece of paper, they managed to put two Core 2 Duo processors onto one piece of silicon. However, while there is direct communication within each dual core processor, there is no direct connection between the two dual core processors. This is one of the reasons why this first quad core is not any faster on many applications (that the software is not written to take advantage of the multicore approach is another). This also has some enthusiasts yelling “foul,” that this approach is not a “true” quad core processor. Semantics aside, unless video editing is your main computer activity, most users should pass on these chips for the time being. When AMD comes out with its long awaited “4 x 4” approach, I don’t expect it to have any more of a direct connection than the Intel part (read my thoughts about it here, and where it fits into this schema).

Now in development is the true quad core processor. This will have the advantage of having all of the cores directly in communication with all of the other cores. Unfortunately, this type of technology is not likely to available until the second half of 2007, and this is not etched in stone. Of course, by the time it’s introduced, we’ll be looking forward to 8 (!) core processors and beyond.So what to buy in the meantime? I think for the time being, the higher end belongs to Core 2 Duo line, and the budget to the lower end Pentium D. For right now, at least pricewise, the Athlon X2 line is occupying a precarious middle ground that only true AMD faithful will seek out instead of the Core 2 Duo parts. On the other hand, users that wait till next year will likely be rewarded with true quad core chips that should really scream.

--Jonas

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AMD, chip, Intel, processor, processor design, Quad core