Intel Core 2 Quad Q8400 CPU Review

by Reads (48,790)
  • Pros


    • Backwards compatibility
    • Lower power consumption
    • Relatively affordable


  • Cons


    • Core i7 still faster
    • Phenom II x4s mostly faster


The Core 2 Quad Q8400 is a 2.66GHz quad-core processor from Intel, built on the new 45nm process with a 1333MHz FSB and 95W TDP. While it might not be the latest Core i7 model, it is a good option if you are looking to just upgrade your processor in an older rig that supports it. Today we take a look at the Intel Q8400 and see what sort of performance increase it brings to a first generation Core 2 Duo desktop previously using a 1.86GHz E6300. Read on to see what we found.


Our test system had the following specifications:

  • Operating system: Windows Vista Business SP2
  • Processor 1: Intel Core 2 Duo E6300 @ 1.86Ghz
  • Processor 2: Intel Core 2 Quad Q8400 @ 2.66GHz
  • Motherboard: ASUS P5B Deluxe Wifi-AP with Intel P965 Express
  • Memory: 3GB DDR2 SDRAM (1GB x 2, 512MB x 2)
  • Hard drive: 80GB Hitachi @ 7200RPM
  • Video card: Gigabyte 7600GT with 256MB GDDR3
  • Power supply: SeaSonic 330W 

The desktop that we chose for this review is a very early Core 2 Duo machine, purchased around the initial launch of the platform back in the summer of 2006. Obviously this desktop can’t support the latest Core i7 processor without replacing the motherboard and RAM, but it can support the Q8400 and retain all of its old hardware. By replacing just the processor we can see exactly what gains can be had in a system that is now pushing 3 years in age…ancient in the computer industry.

Clocked at 2.66GHz, the Intel Core 2 Quad is part of the Yorkfield 45nm series. This processor class features 2MB of L2 cache per side, totaling 4MB. It offers a 1333MHz FSB and 95W thermal envelope. Compare this to the older E6300, which was clocked at 1.86GHz with 2MB of L2 Cache total. It had a 1066MHz front side bus and a lower 65W TDP. Although the E6300 technically has a 30W lower TDP, in some of our tests we actually found the Q8400 to draw less power under different circumstances. This is a side-effect of the newer and smaller manufacturing process.

The desktop used for this review isn’t the latest and greatest by any stretch of the imagination. It is pushing almost three years since it was originally built, which makes everything even more impressive when it can be compared to some of the desktops released in the past year. The main weakness that this machine still has though is its slow NVIDIA GeForce 7600GT graphics card, which even the fastest processor on the planet can’t help.

The first benchmark we ran to get an overall view of system performance before and after the upgrade was PCMark05 and PCMark Vantage. Both benchmarks saw a 50-60% increase moving from the E6300 to the Q8400.


CPU PCMark05 PCMark Vantage
Intel Core 2 Quad Q8400 @ 2.66 GHz 8044 PCMarks 4625 PCMarks
Intel Core 2 Duo E6300 @ 1.86 GHz 5168 PCMarks 3082 PCMarks

Next up is 3DMark06, which as mentioned before, saw little gain to the 3D performance after the processor upgrade. To see this increase we would need to upgrade to a graphics card that isn’t three years old.
When we breakdown the CPU components of PCMark05 and 3DMark06, the Q8400 gives some pretty strong results. Compared to other processors we have reviewed, it falls just above the Phenom x4 9850 BE overclocked to 2.9GHz.

CPU 3DMark06
Intel Core 2 Quad Q8400 @ 2.66GHz 3404 3DMarks
Intel Core 2 Duo E6300 @ 1.86GHz 3159 3DMarks

PCMark05 and 3DMark06 CPU test performance comparison results (higher scores mean better performance)

CPU PCMark05 CPU Test
3DMark06 CPU Test
Phenom II x4 955 @ 3.2 GHz 9693 PCMarks 4242 3DMarks
Phenom II x4 940 @ 3.0 GHz 9020 PCMarks 4241 3DMarks
Core 2 Quad Q8400 @ 2.66 GHz 8459 PCMarks 3888 3DMarks
Phenom II x4 810 @ 2.6 GHz 7750 PCMarks 3684 3DMarks
Phenom x4 9950 BE @ 2.6 GHz 7682 PCMarks 3551 3DMarks
Core 2 Duo E6300 @ 1.86 GHz 4705 PCMarks 1612 3DMarks

Looking at wPrime when comparing the E6300 to the Q8400, we see a huge decrease in test duration. The quad-core processor gives results that are 3 times faster than the original processor.

wPrime benchmark comparison results (lower numbers mean better performance)

CPU wPrime 32 time
Core i7 920 @ 2.66 GHz 9.1s
Phenom II x4 955 @ 3.2 GHz 11.859s
Phenom II x4 940 @ 3.0 GHz


Core 2 Extreme QX6850 @ 3GHz 13.869s
Phenom II x4 810 @ 2.6 GHz 14.397s
Core 2 Quad Q8400 @ 2.66 GHz 14.133s
Core 2 Quad Q9450 @ 2.66 GHz 14.625s
Core 2 Duo E6300 @ 1.86 GHz 43.574s

The final test we ran on the newer processor only, to compare it to some of the faster AMD Phenom processors is our Audio Compression test. The Intel Q8400 compressed the 14 WAV files in 32 seconds, which pairs up close with the Phenom II x4 955.

Audio Compression Test (lower scores mean better performance)

CPU Audio Test (HH:MM:SS)

Phenom II x4 955 @ 3.79 GHz (OC)


Phenom II x4 955 @ 3.2 GHz

Phenom II x4 940 @ 3.0 GHz 00:00:35
Core 2 Quad Q8400 @ 2.66 GHz 00:00:36
Phenom II x4 810 @ 2.6 GHz 00:00:41
Phenom II x3 720 BE @ 2.8 GHz 00:01:22

Besides benchmarks the faster processor helped out in some of the daily tasks seen in my HTPC. Very high bitrate 1080P videos used to have problems with audio sync with the old processor, where midway through a movie the video would be running .5 to 1 second behind the audio. After switching to the faster processor the problems were eliminated. Upgrading to a graphics card that fully supports GPU-assisted MPEG4 decoding would have also probably helped.

Save your old machine
As we mentioned above, the system we used was a stock three- year old desktop into which we just dropped this processor. Just because you have an old rig doesn’t mean it can’t be upgraded to “modern” levels of performance. The processor was the only change in this desktop, with the old (and slow) DDR2-667 RAM, Intel 965P chipset motherboard, and 80GB hard drive still being used and fully compatible. In some systems sold with the Intel P4 processor that have compatible motherboards, this type of upgrade would yield even greater performance boosts. If you took this time to upgrade the graphics card, you could easily have a desktop that would blow most retail machines away for a fraction of the cost.

Just make sure you check the rating of your power supply before you start throwing faster and more power consuming components into an old desktop. If you didn’t over-spec the power supply originally it might be pushed to its limit under stress. Also, be certain that your motherboard would support a processor upgrade. Sometimes, just because the socket on the board matches the processor doesn’t mean it’s compatible, since the CPU must be recognized by the BIOS as well.

Power Consumption
One of the first things I checked after upgrading the processor was how much of an impact the quad-core processor was going to have on my power bill. One might guess that more cores and higher clock speed might equal higher power consumption, but that was only partially true. Under a light load and close to idle activity, which you might see while browsing the web, the original E6300 used 94 watts of power. Under a heavy load of wPrime, power usage jumped to 116 watts. With the Q8400 idle power consumption was 89 watts at idle, 5 lower than the old dual-core. Under a peak load it jumped to 137 watts, much higher, but under normal daily use most people don’t have their processors pegged. For a HTPC which is going to be on and downloading stuff in the background overnight, you will probably end up saving power with the much faster processor.

Overall the Intel Core 2 Quad Q8400 is a strong processor, even when compared with some of the faster offerings from AMD. It lags behind the Core i7 lineup, which we expected, but it is much cheaper and if you have older hardware like I did it is fully compatible. Power consumption dropped moving to the Q8400 from my older E6300. At idle and light load power usage was less, but went higher when the processor was tasked. For the average computer that might spend more time at idle than under 100% load, seeing any drop in power is welcome. If you have an older LGA775 board or just want to build a cheap desktop, the Intel Core 2 Quad Q8400 is well worth looking into, especially if you find it on sale.



All content posted on TechnologyGuide is granted to TechnologyGuide with electronic publishing rights in perpetuity, as all content posted on this site becomes a part of the community.