Platform Flexibility

Okay, let's move away from pure performance metrics and move to something more fundamental. You should not only select a processor based on its performance. You also have to take into account the platform on which it runs on. This determines the other components you need to buy, and your future upgrade options. Let's take a look.

Since processors can limit your ability to enhance and upgrade your system down the line, choosing one that is based on a platform with good upgrade options will probably give you the best bang for your buck. Sometimes, it's just not worth going with a particular processor merely because its platform is slated to be replaced by a new platform. For example, buying an AMD Athlon 64 processor that's based on the Socket 939 and DDR SDRAM when AMD is shifting to the new AM2 socket with DDR2 support.

So, if you want to spare yourself upgrade headaches in the future, plan ahead. Choose a processor that's based on a platform in active development. The easiest way to keep yourself from being left in the lurch is to consult the processor roadmaps by Intel and AMD. Take for example, Intel's processor and chipset roadmap. Taking a look at it will give you an idea of Intel's plans for the next 6 months.

By checking such roadmaps, you can avoid buying processors for platforms that are destined to be phased out soon. If you know that Intel or AMD is going to release a new processor for a particular platform 1-2 years down the road, you can be sure that this platform will not be phased out anytime soon.

Another trick is knowing the right time to buy. Never buy anything when a new platform is slated to be released soon. It would be prudent to save your money and just wait a while. Most chipmakers plan on a chipset or socket life cycle of 3-4 years. So, if you need a rule of thumb, don't buy a platform that is more than 2 years old.

However, you should not rely on this rule of thumb as it greatly depends on marketing and engineering factors. If the newer processors do not require more power or features than the current socket can support, then the chipmaker isn't likely to shift to a new socket. For example, when the Core 2 Duo came along, Intel stuck with the Socket 775 because its power consumption was much lower than the Pentium 4 processor it was replacing.

On the other hand, Intel switched from the Socket 478 to Socket 775 with the debut of the Prescott core because this particular Pentium 4 processor just required more power than the Socket 478 could provide. AMD also switched sockets for the same line of processors, but for a different reason. They switched from the Socket 939 to Socket AM2 for the Athlon 64-series of processors because these processors featured an integrated memory controller. To support DDR2 memory, they had to use a new socket with more pins.

It can seem extremely complex and to be honest with you, this aspect of choosing processors is just that. It's just one of those things you'll have to learn in small steps by using a little common sense, coupled with up-to-date and accurate information on the latest and future development of chipmakers like Intel and AMD. But it's worth taking the time to read up and do a little research. It will save you a lot of money and upgrade hassles in the future.

Performance Per Watt & Heat

As consumers and the computing industry itself become more environmentally-conscious, it's inevitable that pure performance will no longer be the sole factor in determining the desirability of any processor. Power efficiency used to be a major factor only in mobile processors but even now, chipmakers like Intel and AMD are looking to improve the power efficiency of their desktop processors.

Even if you are not worried about global warming, think about the money you will save with a more power-efficient processor. Here we have a comparison of the power consumption of a Pentium D processor and a Core 2 Duo processor.

As you can see, the Core 2 Duo uses half as much power as the Pentium D. 65W less power may not seem like much, but coupled with advanced power-saving features like SpeedStep, it can translate into savings of $80-120 a year... and that's just for the processor.

It's like deciding between a GM Hummer H2 SUV and a Toyota Prius. Both get you from point A to point B, but the Hummer guzzles fuel at the rate of 24L per 100 km (10 mpg) while the Prius only needs about 5L per 100 km (48 mpg). Evidently, the less-efficient Hummer costs more to run than the Prius. Would you prefer to go with the Prius or the Hummer?

But how do you determine which is the more efficient processor? To do that, you need to calculate its performance per watt by dividing any performance metric by the power consumption of the processor. Take for example, the following hypothetical comparison of three processors.

Just looking at the benchmark score and power consumption alone, it's hard to determine which processor is more efficient.

However, if you calculate their performance per watt ratio, you can easily see which processor is more efficient. In this case, processor B is 60% efficient than processor A and over twice more efficient than procesor C. It's the winner hands-down, as far as efficiency is concerned.

You can do this for any benchmark score you wish to compare. Just divide the score by the power consumption. Of course, you should not select processors based on their power efficiency, but a power-efficient processor is always more desirable than one that's less power-efficient.

Now, there are really more advantages to buying a more efficient processor. Not only does buying a less power-hungry processor save you electricity, it allows you to buy a less powerful (and cheaper!) power supply unit. Even more importantly, a processor that uses less power puts out less heat.

Hot processors have a shorter lifespan and makes overclocking more difficult. It also necessitates the use of larger, noisier and more expensive coolers. Overall, going with a cooler processor will not only mean lower costs but also a longer lifespan and greater reliability.

To find out just how much heat a processor produces, you need to look for its Thermal Design Power (TDP). For your convenience, you can take a look at the TDP of various processors at our Desktop CPU Comparison Guide. If you want to look for the TDP of mobile processors, you can take a look at our Mobile CPU Comparison Guide.