NVIDIA GeForce GT 620M vs NVIDIA GeForce GT 650M SLI

NVIDIA GeForce GT 620M

NVIDIA GeForce GT 650M SLI

The NVIDIA GeForce GT 650M SLI is a high-end DirectX 11-compatible graphics solution for laptops, consisting of two GeForce GT 650M. Each card has a 28nm GK107 core based on the Kepler architecture. With SLI, each card usually renders a single frame (AFR mode). Therefore, it may suffer from micro stuttering in low fps ranges of 30fps. This happens because of different timespans between two frames (e.g., irregular delays between sequential frames). The 650M SLI is currently used only in the Lenovo Y500 with fast GDDR5 graphics memory and clock rates of 790 to 835 MHz (GeForce Boost).

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK107 Kepler core offers two shader blocks, called SMX, each with 192 shaders for a total of 384 shader cores that are clocked at the same speed as the central core. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are about as fast as one shader of a Fermi chip (as the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

The gaming performance of the SLI combination ranges between a GeForce GTX 670MX (maximum, e.g. in 3DMark 11 benchmarks) down to a single GeForce GT 650M (if SLI is not supported by the game). On average the 650M SLI could therefore be placed a bit above a Geforce GTX 660M in the high-end class. Modern games of 2012 should therefore be playable with high detail settings.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK107 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENC API.

The power consumption of the GeForce GT 650M SLI should double compared to a single GTX 650M. Therefore, only large laptops can handle the heat dissipation.