Editing Clock rate (section)

==Determining factors==
=== Binning ===
[[File:Clock signal and clock rate.png|thumb|upright=1.8|Representation of a clock signal and clock rate]]
Manufacturers of modern processors typically charge higher prices for processors that operate at higher clock rates, a practice called [[Product binning|binning]]. For a given CPU, the clock rates are determined at the end of the manufacturing process through testing of each processor. Chip manufacturers publish a "maximum clock rate" specification, and they test chips before selling them to make sure they meet that specification, even when executing the most complicated instructions with the data patterns that take the longest to settle (testing at the temperature and voltage that gives the lowest performance). Processors successfully tested for compliance with a given set of standards may be labeled with a higher clock rate, e.g., 3.50&nbsp;GHz, while those that fail the standards of the higher clock rate yet pass the standards of a lower clock rate may be labeled with the lower clock rate, e.g., 3.3&nbsp;GHz, and sold at a lower price.<ref>{{cite patent|country=US|number=6826738|title=Optimization of die placement on wafers|url=http://www.google.com/patents/US6826738}}.</ref><ref>{{cite patent|country=US|number=6694492|title=Method and apparatus for optimizing production yield and operational performance of integrated circuits|url=http://www.google.com/patents/US6694492}}.</ref>

===Engineering===
The clock rate of a CPU is normally determined by the [[frequency]] of an [[Crystal oscillator|oscillator crystal]]. Typically a crystal oscillator produces a fixed [[sine wave]]—the frequency reference signal. Electronic circuitry translates that into a [[Square wave (waveform)|square wave]] at the same frequency for digital electronics applications (or, when using a [[CPU multiplier]], some fixed multiple of the crystal reference frequency). The [[clock distribution network]] inside the CPU carries that [[clock signal]] to all the parts that need it. An [[Analog-to-digital converter|A/D Converter]] has a "clock" pin driven by a similar system to set the [[sampling rate]]. With any particular CPU, replacing the crystal with another crystal that oscillates at half the frequency ("[[underclocking]]") will generally make the CPU run at half the performance and reduce [[waste heat]] produced by the CPU. Conversely, some people try to increase performance of a CPU by replacing the oscillator crystal with a higher frequency crystal ("[[overclocking]]").<ref>{{Cite web |url=http://www.tomshardware.com/reviews/overclocking-guide-part-1,1379.html |title=Overclocking Guide Part 1: Risks, Choices and Benefits : Who Overclocks? |first1=Thomas |last1=Soderstrom |date=11 December 2006 |quote="Overclocking" early processors was as simple{{Snd}} and as limited{{Snd}} as changing the discrete clock crystal ... The advent of adjustable clock generators has allowed "overclocking" to be done without changing parts such as the clock crystal.}}</ref> However, the amount of overclocking is limited by the time for the CPU to settle after each pulse, and by the extra heat created.

After each clock pulse, the signal lines inside the CPU need time to settle to their new state. That is, every signal line must finish transitioning from 0 to 1, or from 1 to 0. If the next clock pulse comes before that, the results will be incorrect. In the process of transitioning, some energy is wasted as heat (mostly inside the driving transistors). When executing complicated instructions that cause many transitions, the higher the clock rate the more heat produced. Transistors may be damaged by excessive heat.

There is also a lower limit of the clock rate, unless a fully [[static core]] is used.