CPU Chipset - Published on Monday, 28 January 2008 00:30 Written by Robert Kihlberg
Higher clock frequencies
There are a number of aspects, which affects how fast a transistor can switch between on and off, which becomes the actual limit of how high clock frequency a processor can work at. Because the transistor gets physically smaller it also requires less current to switch. Another important aspect is interference in the lanes inside the processor. Smaller lanes results in a smaller area towards the surrounding which in turn gives a reduced capacitive load. When this interference is reduced it also lessens the stress on the transistors, which leads to faster switches. The discussion is based on that one doesn't change the voltage between the different manufacturing techniques, which rarely is the case. The voltage has a large impact on how high clock frequency the processor can work at but it also has a impact on the power consumption. Therefore one often chooses a compromise of these; a bit faster and a bit less power hungry.
Lower power consumption
As mentioned above one has the possibility to lower the processor's voltage together with finer manufacturing technology. The formula above shows the connections between frequency, voltage and dynamic capacitance, and how these affect the power consumption of a processor. The dynamic capacitance depends partly on the manufacturing process and partly on the processor's architecture. This parameter cannot be changed when the processor has been manufactured. The voltage affects the power consumption in square, which makes it the absolute most important factor when it comes to reducing the heat dissipation. If we cut the voltage in half the power consumption is reduced by three quarters, while if you double the voltage the power consumptions quadruple. The frequency scales linearly to the power consumption, which means that a doubling of the frequency doubles the power consumption.
This mentioned compromise between clock frequency and voltage has worked satisfyingly in earlier generations. If higher clock frequencies were needed, one increased the voltage and if a low power processor was needed you lowered it. Nowadays the distance between performance processors and low power processors is becoming very big and Intel admits that it is looking closer on alternating the manufacturing process for different types of models, to in turn manufacture processors more specifically to its intended usage.
A great deal in the reduction in power consumption can be related to the new technologies that are used to manufacture the transistor's gate. To take a crash course in how a CMOS transistor works, you could say that the gate controls if current should pass from Drain (D) to Source (S). In other words, the gate is a like a switch. What Intel has done is that it has gone from using silicon in different doped shapes, to a combination of metal and dielectricum. By competitive reasons it doesn't reveal what type of metal is used, and nothing more than that the dielectricum is based on the element Hafnium. We will take a closer look on the power consumption of the processor later in the article and see if these changes have made any difference.
We move on and look at what has been added to the architecture.
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