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Can Legacy Dual-Core CPUs Drive Modern GPUs?
Date: Feb 08, 2013
Author: Joel Hruska
Introduction, Test System
A few weeks back, we examined whether a new GPU like the GeForce GTX 660 could breathe new life into an older quad-core gaming system built in mid 2008.  The answer, we concluded, was definitely yes -- but many of you of you asked us to reconsider the question, this time using a dual-core Core 2 Duo.

We've done so. And just for fun, we've added overclocked CPU results into the mix as well.

The Q6600 we originally tested was one of the best-selling enthusiast processors of its day, but dual-core chips were very much the norm. At the time, there were only a handful of games that could even take advantage of four cores and both Intel and AMD priced by core count. That's changed now, with multiple games using up to four cores.

So, can older Core 2 Duo's still keep up? Let's find out.

The System:

Our test bed, the ASUS Rampage Formula X48 Motherboard, from days of yesteryear.

EVGA's GeForce GTX 660 SuperClocked backing-up the Core 2 Duo with muscle.

The only Core 2 Duo CPU I still had on hand is an Intel E6850. It's a first-generation C2D part based on Intel's 65nm Conroe core. It's clocked at 3GHz with 4MB of L2 cache and has a 1333MHz FSB. If you were to pull Intel's full suite of Core 2 Duo consumer SKUs, the E6850 would have ranked at the upper end of the heap. Performance should be somewhere between the 45nm E7600 and E8400.

We tested the E6850 and Q6600 in the same Asus X48 Rampage Formula motherboard with 3GB of DDR2-1066. An EVGA GTX 260 and GTX 660 were used to compare graphics performance. Our overclocked figures were measured using the Q6600 (SLACR core) with its FSB bumped to 1333MHz, up from 1066MHz.

As before, we present performance figures for the GTX 260 and GTX 660. Overclocked performance with the Q6600 at 3GHz and the GTX 660 is also given. The primary question we want to answer is how much a new GPU can help the performance of an older dual-core CPU. In our default configuration, the Q6600 has twice the cores, but the E6850 enjoys a 25% clock speed advantage.
Battlefield 3, Borderlands 2
Battlefield 3:

BF3 is known for maintaining a consistent frame rate and runs extremely well on older hardware. We benchmarked the game with custom detail settings -- everything was set to "High", save for MSAA, which was enabled at 4x. We benchmarked the Operation Firestorm map in a 64 player game.

Battlefield 3 paints an interesting performance picture. Equipped with a GTX 260, the difference between dual and quad-core configurations is tiny -- and actually favors the 3GHz Conroe. Once we switch to the GTX 660, the tables turn. The GTX 660 delivers a respectable 15% performance boost for the E6850, but the Q6600 pulls ahead in absolute terms.

Overclocking the Q6600 improves the CPU's performance enormously. The gain is noticeable even without Fraps; the game is much smoother.

Borderlands 2:
Borderlands 2 doesn't have presets, so we've dropped in a handy screenshot with the settings we used.

In Borderlands 2, we forced FXAA on via the graphics driver as well as enabling it from in the in-game menu. This somewhat improved the visual quality but didn't impact performance much on either card.

In Borderlands 2, the Q6600 has a significant performance advantage with both GPUs. The E6850 + GTX 260 combination is slow enough to drag noticeably when there's a lot of action on the screen; the Q6600's frame rate dips at these moments, but not to the same degree. Switching to the GTX 660 gives the E6850 a 60% frame rate increase, compared to a gain of 50% for the Q6600. Here, the benefit of overclocking is fairly modest -- a 25% clock speed boost yields a 12.5% performance gain.
Civilization V
Civilization 5:

Civilization V was benchmarked with all settings on high with 4x MSAA enabled. We used the game's built-in Late Game View benchmark. The "Use the GPU for texture decompression" option was checked, but grayed out when testing on the GeForce GTX 260.

Civilization V has major problems running in DX10 mode with the GTX 260; it's not surprising to see the two CPUs tied at 14 fps. Stepping up to the GTX 660 brings the E6850 into playable territory and more than doubles the game's frame rate. The Q6600, however, benefits more -- the quad-core CPU can push the GTX 660 harder than the E6850, despite the latter's clock speed advantage. Overclocking the CPU has no effect; this benchmark is GPU-limited.
Shogun 2
Shogun 2:

Shogun 2 is an immersive RTS game with gorgeous visuals, full support for DX11, and a wickedly long load time if you don't drop it on a solid state drive. We chose to "Benchmark Game Settings" using the "High" preset on both the GeForce GTX 260 and GTX 660. In this case, we also opted to test the GTX 660 using "Very High" details with tessellation and ambient occlusion enabled.

As we've seen several times before, the GTX 260 hits 43 FPS with either CPU. Again, upgrading to a GTX 660 matters for both chips, but the 2.4GHz Q6600 picks up 46% compared to the E6850's 23%. Shogun 2 is also overclocking friendly; pushing the Q6600 to 3GHz improves frame rates by a further 17%.

At Very High Detail, the E6850 has a small advantage over the slower Q6600 when the GTX 260 is installed. The rankings don't change much -- the new GPU is better for both CPUs, but the Q6600 gains more from the exchange. Overclocking has less of an impact here; a 25% clock speed increase only improves frame rates by 9%.
Parsing Results and Upgrade Options
First, let's talk about the big picture. Can you upgrade the GPU on a six year-old dual core machine and expect to see a noticeable improvement in game performance? Yes. We've put together two graphs that summarize the situation.

Here's the average performance increase we saw when upgrading from a GTX 260 to a GTX 660. The quad-core Q6600 benefits more from the upgrade, but the E6850 gains a significant amount of performance as well. Not too shabby.

This graph shows how the Q6600 stacks up against the E6850 when both systems are equipped with the GTX 660.

The Q6600 is, on average, 21% faster than the E6850 when both chips are running at stock clocks. Overclocking the Q6600 also yields positive results. Games that are completely GPU-bound, like Civilization V, gained no performance, but frame rates in Battlefield 3, Borderlands 2, and Shogun 2 increased a further 16%.

Here's the short, non-math version:  A quad-core is significantly better than a dual-core for modern games. An overclocked Core 2 Duo quad-core is meaningfully faster than a stock-clocked variant.

The Cost of Upgrading
Intel Core 2 Q6600 chips aren't available new these days, but Ebay has a ton of them, regularly priced between $50-$70. If you plan to overclock a Q6600, you'll want the G0 stepping (SLACR). Other quad-core variants are also available, including chips based on the 45nm Yorkfield CPU. Price and availability are obviously highly variable and the usual caveats apply when buying from Ebay.

Is a new CPU worth the price? I'd say yes -- especially if you've currently got a dual-core CPU in the 2.2 - 2.6GHz range. The combined cost of a used Q6600 and a GeForce GTX 660 should still come in below $300 while delivering far better performance than any bottom-end desktop you might assemble for that price tag.

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