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…The basic stats for this insignificant-seeming budget processor read as follows: Pentium D 805 clocked at 2.66 GHz, equipped with two processor cores both with 64 bit support. At your friendly neighborhood retailer you can pick up this secret weapon for pocket change – right now, for example, it’s available at newegg.com for just under US$130. We were quite amazed as the first performance figures emerged from our test labs: stable operation was possible at 4.1 GHz, and without even the need for substantial boosts to cooling!…
…The multiplier expresses the ratio between the processor clock speed and the FSB clock. For the Pentium D 805, the combination of FSB and processor clocks results in a multiplier value of 20x. By comparison with other CPUs with 200 MHz or 266 MHz FSB, this is a very high value – 12x and 14x are much more common. But this also makes the Pentium D 805 a good candidate for overclocking. Simply by raising the FSB clock rate to 200 MHz, the resulting CPU clock rate rises to 4.0 GHz once the 20x multiplier is applied (20x times 200 MHz equals 4.0 GHz)…
…NOTE: The 20x multiplier is burned into the CPU and may not be altered using a special BIOS, nor with a hardware jumper on the motherboard…
FSB clock CPU clock
133 MHz 2.66 GHz (Default)
140 MHz 2.80 GHz
150 MHz 3.00 GHz
160 MHz 3.20 GHz
166 MHz 3.33 GHz
170 MHz 3.40 GHz
180 MHz 3.60 GHz
190 MHz 3.80 GHz
200 MHz 4.00 GHz
205 MHz 4.10 GHz
210 MHz 4.20 GHz (THG clock)
…The Pentium D 805 works with a front-side-bus clock rate of 133 MHz (533 QDR). Thus, the design of the chipset dictates a maximum memory clock speed of DDR2-533. But overclocking the front side bus also raised memory clock rates; the actual memory clock rate that results from increasing the FSB clock rate may be calculated using a memory multiplier value. Typical Intel platform memory multipliers vary from 2.0 up to 4.0, and may be set as such. Because our overclocking starts from a very low FSB clock speed, a special set of circumstances emerges for the memory multiplier. Namely, for an FSB clock set between 133 MHz and 148 MHz, the only valid memory multiplier values are 3.0 and 4.0 – lower values make no sense…
…We were able to successfully implement our overclocking project, in fact, using the following motherboards from Asus and Gigabyte:
Asus P5WD2-E Premium (Intel 975x)
Asus P5WD2-WS Premium (Intel 975x)
Asus P5WD2 Premium (Intel 955X)
Gigabyte G1975X Turbo (Intel 975X)
Gigabyte 8I955X Royal (Intel 955X)
…The dark side of overclocking a CPU is the heat produced when consuming enormous amounts of power. Since our Pentium D 805 CPU was built using 90 nm fabrication technology and implements a dual core design, power consumption at clock speeds over 4 GHz climbs to extreme levels…
…By deactivating the C1E energy-saving function in the Pentium D 805, Intel bursts any hope of achieving the same functionality as the Intel Pentium Extreme Edition 965 with 266 MHz FSB. This makes it impossible to use a BIOS modification to achieve an “Enhanced Halt State” and thereby to raise the CPU multiplier any higher than 14x. This would have been an ideal configuration had it been possible: 14 x 266 = 3.73 GHz…
…When compared with the most current models, this CPU doesn’t miss any of the important features. Support for both EM64T (64 bit instructions and execution) and the Execute-Disable function (NX) are both present. The Pentium D 805 is a dual core architecture, so it can do without Hyper Threading and not take too big a penalty. The only new feature that’s missing that might be of some concern is Intel’s Virtualization Technology (VT). This reflects Intel’s well-known practice of building only a single core, but then deactivating various functions to serve different price segments….
…3.33 GHz Remains Stable At Standard Voltage Levels
Initial excitement begins when raising the speed of the FSB from 133 to 166 MHz. To our utter astonishment, the CPU ran at a clock rate of 3.33 GHz without any problems at standard voltage levels of 1.3375 V, even when both cores were fully loaded…
If the CPU is heavily loaded for some time, however, the system inevitably crashes because of overheating… After abandoning the Intel box cooler, we chose a Zalman model instead. We recommend the CNPS9500, one of the best coolers available on the market today…
Overclocking the FSB clock rate to 180 MHz improves memory performance. The highest memory clock at our disposal is 360 MHz, because a maximum memory multiplier of 4.0 translates into DDR2-720. Thus, we improved memory performance by 35 percent, as company to the original memory clock rate.
Now we observe a noticeable increase in power consumption for the entire system. In idle mode, energy use climbs by 33 W; we also measured 204 W of power consumption from the power supply. Under heavy load, power consumption increases by a hefty 101 W. In considering the fact that about 80 percent of this 101 W goes to the CPU, we observe that energy consumption at 3.6 GHz has doubled to 160 W. We find ourselves here running at nearly 30 W above the maximum power class for dual core processors based on this CPU core, according to Intel’s specifications.
We continued our attempts to increase the speed of the FSB clock rate and boot the system at 190 MHz FSB. We could no longer sustain stable operation at this speed, which led us to boost CPU core voltage levels. We raised the voltage in steps of 0.025 V until the processor could operate without crashing at peak load. We achieved this goal when the voltage levels reached 1.500 V, or 0.1625 V above the standard level.
To keep the system stable at a 50 percent overclocking level, we had to increase the core CPU voltage yet again. We took the same incremental approach described in the preceding section. Finally, when the voltage was increased by 0.2875 V, the system continued to be stable at 4 GHz, even at maximum load!… It was clear that air cooling solutions were no longer sufficient to let the system function at 4 GHz in all situations, so we switched to a water-cooled solution for this CPU. It worked!…
…Although the Pentium D 805 offers only a 1 MB L2 cache, its CPU clock is also 276 MHz faster than the top-of-the-line Pentium EE 965 (equipped with 2 MB L2 cache); this enables the 805 to outperform the pricier chip.