NVIDIA GeForce 840M vs NVIDIA GeForce 940MX

NVIDIA GeForce 840M

The NVIDIA GeForce 840M is a 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 (GM108 chip), but is still manufactured in 28 nm. The 840M offers 384 shader units clocked at 1029 MHz (+ Boost) as well as 2 GB of DDR3 memory (64 bit, 2000 MHz effective).

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. GM108 features 3 SMMs and thus 384 shader cores, 24 TMUs and 8 ROPs (64-bit interface).

Another optimization is the massively enlarged L2 cache. The larger size can process some of the memory traffic to allow for a relatively narrow memory interface without significantly reducing performance.

Similar to Fermi and Kepler, the GM107/GM108 support DirectX 12 with feature level 11_0 only.

Performance

According to our benchmarks, the GeForce 840M is about 30 percent faster than the old GT 740M and just slightly behind a GeForce GT 750M (DDR3 version). Many games of 2013/2014 can be played fluently in WXGA resolution (1366 x 768) and medium or high detail settings. However, very demanding games such as Crysis 3 or Battlefield 4 will require lower resolutions and/or details.

Features

GM108 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 840M should be about 30 Watts or lower. Therefore, the GPU is best suited for laptops 13 - 14 inches in size and above. The 800M series also supports Optimus to automatically switch between an integrated graphics card and the Nvidia GPU.

NVIDIA GeForce 940MX

The Nvidia GeForce 940MX is a mid-range laptop graphics card with DirectX 12 support (FL 11_0). It has been announced in the first quarter of 2016 and is the refresh of the GeForce 940M. Compared to the older card, the new one is based on the same chip but now supports faster GDDR5. Therefore, it is similar to the Maxwell GPU in the Microsoft Surface Book but with more memory and higher clock speeds. However, most notebook vendors will use the slower DDR3 version of the 940MX that clocks only a few percent faster than the old GeForce 940M (1122 versus 1072 MHz base clock e.g.). 

For the GDDR5 version of the 940MX there appears to be also a variant with the GM107-B chip with 512 shaders instead of the 384 but lower clock speeds. The 940MX in the Acer Aspire E5-774G e.g. featured 512 shader cores (GM107) clocked at 795 - 861 MHz. The Dell Inspiron 17 7778 version however had the GM108 chip with 384 shaders clocked at 1083 - 1189 MHz.

The performance greatly depends on the used graphics memory and chip. According to our benchmarks (see below), the DDR3 version is very similar to the old 940M (due to only minor increased clock rates). The GDDR5 version however pushes ahead 20% (even 30% if paired with a fast desktop quad-core, but we lack 940M reference scores). Therefore, demanding games from 2015 should run fluently in low to medium settings and WXGA resolution. 

The TDP of the card should be rated at about 15 to 30 Watt (depending on the version, clock speeds and memory). Therefore, the GPU is best suited for laptops from 13-inch and up.