With the recent release of the GeForce GTX 660 Ti, Nvidia quietly released its GeForce GTX 660 for OEM use only. The graphics card bares similar specifications as its bigger brother the GTX 660 Ti, which might be signs of what is to come if a retail version is released. However, take that with a "grain of salt", as Nvidia has in the past changed specifications from OEM version to retail version, such as different clock speeds or CUDA cores.
Taking a look at the GTX 660 OEM specs, we see it's based on the same GK104 silicon as the GTX 660 Ti with two SMX units disabled, resulting in 1,156 CUDA cores and 96 texture units. The GPU core is clocked at 823 MHz (888 MHz GPU Boost), which is about 10 percent lower than the GTX 660 Ti. The memory is clocked at 5.80 Gbps GDDR5, with a 192-bit memory bus width. The GTX 660 OEM offers memory options of 1.5 GB and 3 GB compared to the GTX 660 Ti's 2 GB configuration. With the decrease in specifications, we see that the GTX 660 OEM only requires one PCIe power connector and a maximum power requirement of 130 W. The other specifications are consistent with the GTX 660 Ti and the other members of the Kepler-based GPUs. With its specifications, it should put the performance of the GTX 660 OEM around about 70 to 80 percent of the GTX 660 Ti.