Testing and Overclocking

We were only able to get our hands on two of the new range of Clarkdale CPUs for this article – the 3.33GHz Core i5-661 and the 2.93GHz Core i3-530. As the Core i5-750 and AMD Phenom II X4 965 Black Edition are close to the Core i5-661 in price, and the AMD Athlon II X4 630 costs a similar amount to the i3-530, we’ve included their results in the graphs.

As we’ve updated our test kit to run on Windows 7, we’ve re-tested the Core 2 Duo E7400 and Core 2 Quad Q6600 to see if the new Intel CPUs are worthy successors.

Test Setup


Here is a list of the applications we've used for our testing - most of them are available free for public consumption, although some are popular professional software applications.
We've used Windows 7 Ultimate 64-bit, as this is the most flexible and reliable 64-bit OS for testing the applications above.


It's impossible to construct a set of test kit that's common across LGA1366, LGA1156, LGA775 and Socket AM3, but we have strived to keep as many components consistent as possible:

Common Hardware

  • ATI Radeon HD 5870 graphics card (Catalyst 9.11 WHQL)
  • 1TB Seagate Barracude 7200.12 hard disk
  • PC Power & Cooling 750W PSU

Intel LGA1366 (Core i7) Hardware

LGA1156 (Core i5, i3) Hardware

  • Gigabyte GA-p55M-UD2 motherboard
  • 4GB (2 x 2GB) Corsair XMS3-1600 memory (1,600MHz, CL9 DDR3)
  • Titan Fenrir TTC-NK85TZ

AMD Socket AM3 (Phenom II, Athlon II) Hardware

LGA775 (Core 2) Hardware

We also overclocked each CPU to its highest stable frequency – and collated all the figures in a handy Overclocking Reference table (see below).

When overclocking the Clarkdale CPUs however, we hit a few issues. As with Lynnfield, it’s not possible to overvolt the uncore area, but unlike Lynnfield it is possible to decrease the frequency of the uncore area of a Clarkdale CPU. This means that while a Lynnfield overclock can be limited by how fast the uncore area can operate at stock voltages, there’s no such overclocking limitation with Clarkdale.

As we wanted to directly compare Lynnfield and Clarkdale performance, we tested all the LGA1156 CPUs in Gigabyte’s GA-P55M-UD2 as this is one of the best LGA1156 boards we’ve found so far. Gigabyte sent us the P6 BIOS for this board, but we couldn’t use a Base Clock of more than 160MHz with either Clarkdale CPU – no amount of voltage or tweaking would make the board stable, and the CPUs were 40-50˚C off their Tjunction thermal limits so they weren’t overheating.

Dropping the CPU multiplier didn’t resolve the issue. It’s early days with Clarkdale, though, and we expect that future BIOS updates will unlock more overclocking potential. We therefore only managed to overclock the Core i5-661 from 3.33GHz to 4GHz, and the Core i3-530 from 2.3GHz to 3.5GHz, using a 159MHz Base Clock.
 Overclocking Reference
 CPUStock frequencyMaximum OverclockOther Adjusted FrequenciesAdjusted Voltages
 Intel Core i5-7502.66GHz (20 x 133MHz)4.15GHz (20 x 205MHz)QPI Ratio: x32 (6.56GHz), RAM: 1,640MHzCPU: 1.475V, PLL: 1.9V, QPI/Vtt: 1.37V, RAM: 1.66V
 Intel Core i5-6613.33GHz (25 x 133MHz)4GHz (25 x 159MHz)QPI Ratio: x32 (5.1GHz), CPU-NB: x12 (1.91GHz), RAM: 1,590MHzCPU: 1.375V, PCH: 1.16V
 AMD Phenom II X4 965 Black Edition3.4GHz (17 x 200MHz)3.99GHz (16.5 x 242MHz)CPU-NB and HT Link: 11x (2.66GHz), RAM: 1,613MHzCPU: 1.5V, CPU-NB: 1.35V, SB: 1.35V
 Intel Core 2 Quad Q66002.4GHz (9 x 266MHz)3.7GHz (9 x 411MHz)RAM:822MHzCPU: 1.55V, RAM: 1.9V
 Intel Core i3-5302.93GHz (22 x 133MHz)3.5GHz (22 x 159MHz)QPI Ratio: x32 (5.1GHz), CPU-NB: x12 (1.91GHz), RAM: 1,590MHzCPU: 1.35V, PCH: 1.16V
 AMD Athlon II X4 6302.8GHz (14 x 200MHz)3.71GHz (14 x 265MHz)CPU-NB and HT Link: 10x (2.6GHz), RAM: 1,600MHzCPU: 1.5V, CPU-NB: 1.35V, SB: 1.37V
 Intel Core 2 Duo E84003GHz (9 x 333MHz)4.25GHz (10.5 x 405MHz)RAM: 810MHzCPU: 1.5V, RAM: 1.9V

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