The E6400 up close

As we mentioned earlier, Intel’s Core 2 E6400 shares all the key architectural features found in the more expensive Core 2 line, only it ships with half the cache and a slower clock speed. When discussing the cache, it’s important to remember that for Core 2, Intel has moved over to a unified L2 cache, meaning the pool of the processor’s L2 memory is shared between both processor cores. The L2 cache can be allocated dynamically to each of the processor’s cores as-needed; say for instance if one core needs more cache than the other. This unified approach also increases efficiency – if both cores need the same data it’s available in one place the each core can access rather than duplicating it in both core’s L2 cache as done with previous approaches.

Core 2’s shared L2 cache also helps to reduce power by minimizing memory traffic.

The Core 2 Duo E6400 chip

Core 2 Duo E6400 and 939 X2 4200+

Overclocking the E6400

Everyone likes the idea of free performance, especially when you’re dealing with lower-end CPUs. After all, with a few keystrokes in BIOS, you can turn your “low-end” CPU into a processor capable of outperforming the latest and greatest CPUs with the right system components and a little bit of knowledge on the relationship between the CPU, front-side bus (FSB), and memory bus. That’s why we were eager to see how far we could push the Core 2 Duo E6400, and it didn’t disappoint.

We started by seeing how far we could push the CPU’s clock speed without adjusting voltage. After a little bit of work within the BIOS of ASUS’ 975X-based P5W DH Deluxe we settled on a FSB speed of 381MHz, for a CPU clock of 3.05GHz – that’s just shy of 1GHz on stock voltage! CPU temps at that clock speed topped out at 39 degrees Celsius at load.

Max OC at stock voltage

3.4GHz on air

To push the CPU even further we had to up the voltage. After slowly cranking up the FSB speed we finally hit 3.4GHz at 1.5V with a 425MHz FSB (8.0x425MHz). We were actually able to run Windows and various apps at speeds as high as 445MHz and higher voltage, but in order to complete our looped 3DMark run for stability we had to settle for 425MHz. CPU temps at that speed were around 53 degrees Celsius at load. Components used to hit these speeds were the aforementioned ASUS P5W DH Deluxe motherboard, a retail B2-stepping Core 2 Duo E6400 CPU, 2GB (2x1GB) Corsair TWIN2X2048-6400C3 DDR2 memory, and finally, Zalman’s massive CNPS7700-Cu CPU fan which features an all-copper design and a large 120mm fan.

Our test system setup with C2D E6400

Keep in mind that we’re running all of our Core 2 performance tests with the memory bus running as close to the official speed of 667MHz as possible (including the OC’ed results), but as we showed in you in our Tweaking Core 2 For More Performance article, you can easily dial in memory speeds of 800MHz or 1066MHz if you’re looking for even more performance.