Picking a processor

I have been receiving an increasing number of emails from users asking for advice on choosing a good processor – particularly from those who are baffled by the many brand names that are available.

There are many varieties of processors in the market made by Intel alone, ranging from Pentium 4 to Core 2 Duo, including Celron, Celeron Duo, Pentium D, Centrino and Core Duo. AMD has their own range of processors too, which includes the Semphron, Athlon and Turion with their X2 (Dual core) versions. The price of one Intel Core 2 Duo system may vary significantly from another Intel Core 2 Duo system, making maters a whole lot more complicating even for computing professionals who haven't been following the evolution of these processors closely. Today I will give you a few tips about the Intel Core 2 Duo range of processors, including their functionality and how you could upgrade to one.

Computer chip makers have long been trying to achieve the conflicting goals of reducing the power consumption of their processors while increasing their processing power. The strategy of packing in more and more transistors on the silicon wafers has helped them expand the instruction set and increase the clock speed of their processors; thereby increasing their processing power has worked for them over many years. The rules of the game are changing now. On the other hand, the affordability and increasing popularity of mobile computing in particular – together with the relatively slow progress of battery technology, has created a demand for energy-efficiency, putting pressure on chip makers to come up with alternative processor technologies that will not consume more power as their speed increases.

The two key factors that contribute towards a processor's power consumption is the transistor count and clock frequency. That is because transistors consume most of their power when they switch from one state to another – so the more transistors a processor has and the more often they switch, the more power the processor will consume. So how can you increase performance while reducing power consumption? The elegant answer lies in the Intel Core 2 Duo processor line which has reduced clock speed while increasing the average number of instructions that can be executed in a single clock cycle. Intel boasts that their Core 2 design philosophy is to achieve 40% lower power consumption for every 40% of increase performance.

Decreasing the frequency is one way of reducing power consumption, but there are also other ways to streamline the use of power at the logical level. Core 2 Duo processors can shut down parts of the processor that are not in use. However, there is a slight performance penalty in powering up these shutdown parts of the processor, so some of these features are turned off in the desktop versions that do not have as rigorous power saving needs as mobile devices.

Another feature of the Core 2 Duo range that makes it popular is that it comes in the same LGA775 package as the Pentium D and Pentium 4 processors, as seen in many existing motherboards that support Core 2 Duo processors after a BIOS upgrade. Even though Core 2 has cherry-picked a few design features from previous processors, its dual core functionality has been designed from the ground up when Intel realised that increasing clock speed with their NetBurst pipeline architecture, will lead to unacceptably high levels of power consumption without yielding significant performance gains.

The biggest single factor that enables Core 2 Duo processors to improve performance is "wide dynamic execution." This means that each step of the "fetch, decode, execute" cycle is wider than before; allowing it to cope with four standard instructions simultaneously, whereas previous designs had a three-wide instruction engine. It also uses a sophisticated scheme to operate speculative and out of order execution as well as branch prediction. These powerful processors on the other hand are well supported with increased L2 cache memory and a faster Front Side Bus.

The cache memory is shared between the two cores which means, that if one core is idling, the other has full access to the cache. It is also optimised so that if both cores need the same data, it is not loaded twice. The bandwidth between the L1 and L2 cache has also been doubled from previous Core Duo architecture.

Core 2 Duo's specialist SIMD (single instruction, multiple data) instructions and registers is called "Advanced Digital Media Boost" and incorporates MMX, SSE, SSE2 and SSE3 technology. Its performance has been increased to allow a 128-bit execution step to complete in one clock cycle rather than two.

In the coming weeks, I will take you through the different models of the Core 2 Duo processor range as well as the new line of AMD processors in the market. Please keep writing in with your questions and comments to technopage@gmail.com