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How is processor speed determined.

by Scott Swinyard / July 7, 2004 6:19 AM PDT

How does a manufacturer determine the speed at which a processor runs. Is it some specific formula, or do they just put it together and choose a speed to set based on how it runs?

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Re: How is processor speed determined.
by R. Proffitt Forum moderator / July 7, 2004 6:24 AM PDT

You didn't give much to work with. From a consumer standpoint, MegaHertz and now GigaHertz works well. From another perspective BENCHMARKS are found by the handful.

Which would you like to use?

Bob

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Re: That isn't what I meant.
by Scott Swinyard / July 7, 2004 6:30 AM PDT

My cpu runs at 2.53 gigahertz. How did Intel know that that was how fast it was supposed to go.

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Not a simple answer but first
by Ray Harinec / July 7, 2004 6:57 AM PDT

one must understand that a 2.5 Ghz signal can really run over printed circuitry for fractions of inches without becoming totally distorted.. Thus when the Mfr designs the chip and selects the line width of the circuitry that sets up the upper limit of frequencies that will work. [try to send a 2.5GHz sqare wave from one end of a 2 inch wire to the other and the signal at the other end is totally unrecognizable]. So basically its the geometry of the chip artwork and the laws of physics as they apply to transmission of signals.

The mfr's years of experience have allowed them to understand the limits of each new technology jump.

The actual specificvalue is generally determined by the memory speeds available, 100, 133, 166, 200 et al.

The CPU has a builtin multiplier that multiplies the clock speed up to the CPU clock speed. The multipliers are usually in 0.5 increments, thus the CPU frequency will be Z.0 or Z.5 times Z is an integer]the memory clock rate. Years ago the mobo had circuitry on it to allow one to change the multiplier. Both AMD and Intel started using fixed multipliers a few yearts ago. They can't be changed [was one of the wys to overclock].

So your CPU at 2.53 Ghz [2533 MHz] is arrived at [if you are using the correct FSB frequency. Using a lower memory frequency will cause the CPU to run slower [the lower clock rate times the multiplier].

If your CPU runs at 2.53 using 133 MHz DDR memory the multiplier is 19. [or 266 times 9.5]. Some mobo BIOS's use the basic DDR clock 100, 133, 166. Some use the double data rate 200, 266, 333 et al] to set the CPU rate, even though in actuality there is a single value multiplier, just a different way to have you set the memory FSB.

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"A Clock sets the TIME"
by nworley / July 7, 2004 6:59 AM PDT

Scot:

The processor obeys the direction of a clock signal that a circuit on the motherboard generates. This clock circuit usually consist of a Quartz Crystal (not always) that oscillates (Ticks)at a certain rate that is turned into a pulse code that the processor is taught to execute instructions by. This clock cycle can be multiplied a certain number of times by additional circuitry before it reaches the processor. This multiplied frequency reaches the megahertz range or millions of ticks per second. Intel by designing the components of the processor has determined by experimentation that the processor runs best at 2.53 gigahertz (clock ticks) and remains stable. Overclockers by increasing the clock cycles can cause the processor to run a little bit faster, but run the risk of overheating the processor, and of course causing the processor to be unreliable. In certain cases Intel has seen fit to lock the processor to prevent anyone from exceeding that rated speed.

Norm

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Re: So it's experimentation...
by Scott Swinyard / July 7, 2004 7:12 AM PDT

And not a specific value determined by the design of the given chip.

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Re: So it's experimentation...Sort of.
by R. Proffitt Forum moderator / July 7, 2004 7:24 AM PDT

When I was involved in chip design, we put a simple speed test circuit to measure the maximum speed through a test circuit across the chip. From the response time we measured, we could "grade" the chip and make a suggestion as to the maximum clock value it could run at across it's temperature range.

Some think that we have evolved to the point where chip engineers and chip fabricators came tell you the maximum clock speed at some temperature and voltage before the chip is made.

The truth is they can only guess.

Bob

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Re: ok
by Scott Swinyard / July 7, 2004 7:59 AM PDT

I saw Ray's "Not sure how you concluded that" post before I saw this, but this has satisfied my curiosity for the moment...

So... the absolute optimum may not be what is running by default, but it should be close.

Thanks.

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Not quite sure how you concluded that.
by Ray Harinec / July 7, 2004 7:32 AM PDT

Again the exact 3 decimal place number is determined by using a finite multiplier to a single decimal point zero or 5.

The speed that the CPU artwork can support is determined by the geometry of the artwork [line thicknesses et al] in microns and going to nanometers. The mfr's have scientists that are fully conversant with the phyics needed to go faster and faster. Creating mfg equipment that can produce the devices with high yields and reliability is also a big part of the equation.

The next is yield off the production line. If the run of chips do not provide a high enough percentage of sellable CPU's they drop them down to the speed of the next lower multiplier setting. But the value is always the multiplier times the available memory clock speeds. For non overclockers the only allowable values are the memory bus times the one decimal place multiplier, no values in between.

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Re: Let me put it this way...
by Scott Swinyard / July 7, 2004 7:47 AM PDT

Then there is a native speed that any given cpu will run at determined by its structure and that's what they manufacturer designates it as. Then you set it up accordingly in your system. That speed is not determined by the manufacturer through experimentation to see what runs best as the other fellow said.

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Re: How is processor speed determined.
by JMarchi / July 8, 2004 12:20 AM PDT

When they manufactured the chip they manufactured it with the specifications required to run at that speed and besides that they lock the multiplier so it won't run faster (though you can push the bus speed with some motherboards and get more speed).

There are many technical apsects of CPU speed but like every other complex item, year over year of improvements and design changes makes speeds higher and higher. Things like widths of traces (which are not really wires inside chips), distances between components inside a chip and the number of components are just part of what decide what speed a processor will run.

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Re: Yeah I wanted to know if..
by Scott Swinyard / July 9, 2004 2:35 PM PDT

they precisely determined what made it run at said speed and set it up to run that way. It would seem to me there would be a precise set of factors that would determine this even though a cpu can obviously be set to run at various different speeds within a certain range.

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