NVIDIA GeForce GTX 880M SLI vs NVIDIA GeForce GTX 860M

NVIDIA GeForce GTX 880M SLI

The NVIDIA GeForce GTX 880M SLI is a high-end DirectX 12-compatible graphics card for laptops, consisting of two GeForce GTX 880M. Each card has a 28nm GK104 core based on the Kepler architecture. The clocks for the SLI-setup are usually identical to a single GTX 880M. With SLI, each card 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).

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK104 Kepler core offers eight shader blocks, called SMX, that are clocked at the same speed as the central core. In the GTX 880M, all eight blocks are active for a total of 1536 CUDA cores. Although the Kepler architecture can utilize more shader cores than a Fermi chip, its shaders can 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 of similar speed to one shader of a Fermi chip (as the latter is clocked twice as fast).

The mobile Kepler series supports PCIe 3.0 as well as an optional Turbo mode, which can automatically overclock the card if the laptop cooling system allows it. This boost is supported by every GeForce 800M GPU.

Performance

Similar to our single GPU benchmarks, the GTX 880M SLI outperforms the GeForce GTX 780M SLI by about 10 percent. This makes the SLI configuration of two GTX 880M the currently fastest mobile graphics solution on the market (as of early 2014). With good driver support, SLI almost doubles the performance of a single card, allowing fluent frame rates even with FullHD resolution and highest detail settings.

Features

The feature set includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can 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 GK104 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.

Power Consumption

The power consumption of the GeForce GTX 880M SLI should double to at least 200 Watt (including board and memory) compared to a single GTX 880M. Therefore, only large desktop replacements can handle the heat.

NVIDIA GeForce GTX 860M

The NVIDIA GeForce GTX 860M is an upper mid-range, DirectX 12-compatible graphics card for laptops unveiled in March 2014. It is one of the first cards based on Nvidia's new Maxwell architecture (GM107 chip), but is still manufactured in 28 nm. The GTX 860M offers 640 shader units clocked at 1029 MHz (+ Boost) as well as 4 GB of GDDR5 memory (128 bit, 5000 MHz effective).

Alternatively, there is also a version based on the Kepler chip GK104, which has 1152 shader units clocked at 797 MHz.

Architecture

Compared to Kepler, Maxwell has been optimized in several details to increase power efficiency. Smaller Streaming Multiprocessors (SMM) with only 128 ALUs (Kepler: 192) and an optimized scheduler should lead to better utilization of the shaders. Nvidia promises that a Maxwell SMM with 128 ALUs can offer 90 percent of the performance of a Kepler SMX with 192 ALUs. GM107 features 5 SMMs and thus 640 shader cores, 40 TMUs and 16 ROPs (128-bit interface).

Another optimization is the massively enlarged L2 cache (GM107: 2 MB). The increased size can handle some of the memory traffic to allow for a relatively narrow memory interface without significantly reducing the performance.

Similar to Fermi and Kepler, Maxwell / GM107 supports DirectX 11.2 with feature level 11.0 only.

Performance

Although the GTX 860M has much less memory bandwidth and computing power, it can compete with (or sometimes even beat) the old Kepler-based GeForce GTX 770M while drawing significantly less power. Many games of 2013/2014 (Tomb Raider or BioShock Infinite, etc.) can be played fluently in FullHD resolution and very high detail settings. However, very demanding games such as Crysis 3 or Battlefield 4 will require lower resolutions and/or details.

Despite its considerably higher shader count, the Kepler version is about 10 percent slower, mainly due to the worse bandwidth efficiency.

Features

GM107 integrates the sixth generation of the PureVideo HD video engine (VP6), offering a better decoding performance for H.264 and MPEG-2 videos. Of course, VP6 supports all features of previous generations (4K support, PIP, video encoding via NVENC API). Unfortunately, HDMI 2.0 is still not supported.

Power Consumption

The power consumption of the GeForce GTX 860M should be similar to the old GTX 765M (about 60 watts). The low-clocked Kepler version draws just slightly more power. Therefore, the 860M is best suited for 15-inch laptops or larger. The 800M series also supports Optimus to automatically switch between an integrated graphics card and the Nvidia GPU.