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Texture filtering
Before we get into game benchmarking, let's run through some synthetic tests to get a better sense of the GT 640's capabilities.

  Peak bilinear
filtering
(Gtexels/s)
Peak bilinear
FP16 filtering
(Gtexels/s)
Memory
bandwidth
(GB/s)
GeForce GTS 450 25 25 98
GeForce GTX 550 Ti 29 29 98
GeForce GTX 550 Ti Cyclone 30 30 103
GeForce GT 640 29 29 29
Radeon HD 7750 26 13 72

The GeForce GT 640's low memory bandwidth is no handicap in these texture filtering tests. Kepler's relatively strong texturing performance puts the GT 640 ahead of the Radeon HD 7750, especially in FP16 filtering, where the AMD card's peak theoretical throughput is half its integer rate.

Tessellation

  Peak
rasterization
rate
(Mtris/s)
Memory
bandwidth
(GB/s)
GeForce GTS 450 783 98
GeForce GTX 550 Ti 900 98
GeForce GTX 550 Ti Cyclone 950 103
GeForce GT 640 900 29
Radeon HD 7750 800 72

In this tessellation test, the GT 640 manages to outpace the 7750 and the older GeForce GTX 550 Ti Cyclone—a card that has both greater memory bandwidth and higher peak theoretical rasterization performance. This isn't the first time we see a Kepler part zoom ahead of the competition in this test.

Shader performance

  Peak shader
arithmetic
(TFLOPS)
Memory
bandwidth
(GB/s)
GeForce GTS 450 0.7 98
GeForce GTX 550 Ti 0.7 98
GeForce GTX 550 Ti Cyclone 0.7 103
GeForce GT 640 0.7 29
Radeon HD 7750 0.8 72

GPU computing

The GT 640 falls behind in these tests, which are chiefly designed to gauge its shader performance. Considering these three cards all have roughly comparable peak theoretical throughput, the GT 640's low memory bandwidth is likely a bottleneck here.

Of course, the Radeon HD 7750 has a huge advantage in LuxMark regardless, even over the GeForce GTX 550 Ti. We've seen a similar pattern with high-end Radeon HD 7800- and 7900-series GPUs stacked up against the GTX 680 and older GeForces in this test. Nvidia has told us it doesn't optimize its drivers for LuxMark, which likely explains the discrepancy.

Let's now see how things shake out in some actual games.