How to calculate how fast your PC really is.
The advertised clock rate isn't the real external CPU clock. For example, Athlon XP 3200+ is said to have a 400 MHz external clock, but in fact its clock rate is 200 MHz transfering two data per clock, making it a processor with a performance similar if the CPU used an external 400 MHz clock but transfering just one data per clock.
Intel CPUs use a technique called QDR or Quad Data Rate, which transfers four data per clock cycle. With this technique the CPU achieves an external performance four times greater than if it was transfering just one data chunk. Because of that, the clock advertised by Intel is four times greater than the real clock used by the CPU. It is still a mystery whether the very high-end 1,066 MHz CPU uses a 400 MHz x 4 bus or a 200 MHz x 8 bus configuration. Maybe the latter, due to the physical difficulties involved in increasing the CPU external clock rate. So, a Pentium 4 processor with 533 MHz bus runs at 133 MHz but achieves a performance "as if" it was running at 533 MHz.
Double Data Rate (DDR). With this technique the CPU transfers two data per clock cycle, doubling the performance of the bus since usually just one data is tranfered per clock tick.
External Clock" is the clock speed advertised by the manufacturer, while "Real Clock" is the real clock signal speed used by the CPU.
Since it is hard do compare clocks when you don't know how much data is transferred per time, it is better to know the maximum transfer rate, given in megabytes per second. The formula to calculate it is rather simple:
Real clock x number of data transferred per clock x 64 divided by 8.
64 is used because the CPU communicates with the memory 64 bits per time, and we have to divide by eight to have the result in bytes.
Example- 400 X 2 X 64/8 = 6400 MB/s
Or else use CPU-Z software (downloaded as cpuz.exe on 31 jan 08)
Run it and check the external clock speed of your CPU on the "Bus Speed" field and check what is its maximum transfer rate.
Intel CPUs use a technique called QDR or Quad Data Rate, which transfers four data per clock cycle. With this technique the CPU achieves an external performance four times greater than if it was transfering just one data chunk. Because of that, the clock advertised by Intel is four times greater than the real clock used by the CPU. It is still a mystery whether the very high-end 1,066 MHz CPU uses a 400 MHz x 4 bus or a 200 MHz x 8 bus configuration. Maybe the latter, due to the physical difficulties involved in increasing the CPU external clock rate. So, a Pentium 4 processor with 533 MHz bus runs at 133 MHz but achieves a performance "as if" it was running at 533 MHz.
Double Data Rate (DDR). With this technique the CPU transfers two data per clock cycle, doubling the performance of the bus since usually just one data is tranfered per clock tick.
External Clock" is the clock speed advertised by the manufacturer, while "Real Clock" is the real clock signal speed used by the CPU.
Since it is hard do compare clocks when you don't know how much data is transferred per time, it is better to know the maximum transfer rate, given in megabytes per second. The formula to calculate it is rather simple:
Real clock x number of data transferred per clock x 64 divided by 8.
64 is used because the CPU communicates with the memory 64 bits per time, and we have to divide by eight to have the result in bytes.
Example- 400 X 2 X 64/8 = 6400 MB/s
Or else use CPU-Z software (downloaded as cpuz.exe on 31 jan 08)
Run it and check the external clock speed of your CPU on the "Bus Speed" field and check what is its maximum transfer rate.
posted by Surinder Rinku at
4:13 AM
