GeForce 8400GS: The NVIDIA GeForce 8400GS is a low-end GPU from 2007. I had picked up this very cheap GPU when carrying out NVIDIA VDPAU video decoding tests to see if this budget product was enough for handling video playback on the GPU, which it was, thanks to NVIDIA's great Linux video API and implementation. The GeForce 8 series was NVIDIA's first product line built on their unified shader architecture and carried codenames in the G80/G90 series. The GeForce 8400GS is on the G86 core and is clocked at 450MHz with an 800MHz memory clock. The low-profile graphics card had 256MB of DDR2 video memory. This particular low-profile GeForce 8400GS built by ASUS was passively cooled with an aluminum heatsink.
Generally, the GeForce 8 series support in the NVIDIA Linux binary driver is great and can take full advantage of the GPU, including VDPAU, CoolBits overclocking, power management, SLI, and other features. The Nouveau support for the GeForce 8 series is generally good too. Obviously it's not as well optimized as NVIDIA's official driver and doesn't support features like VDPAU and SLI, but the GeForce 8 series tends to be among the well-working GPUs on the Nouveau stack. However, there are exceptions and depending upon the Linux kernel / Mesa, there can be some definite pain points. As I have said many times before, using the Nouveau driver can sadly be like a game of Russian Roulette.
GeForce 8500GT: The GeForce 8500GT is another G86 product and is rated to run at 450MHz with 800MHz 256MB DDR2 video memory. The GeForce 8500GT from Gigabyte is a full-height graphics card, but it is passively cooled. Unfortunately, this particular graphics card is highly unstable with the Linux 3.2 kernel / Mesa 7.12 combination used for testing. Other GeForce 8 series GPUs would work, aside from an occasional lock-up that resulted in restarting the system and carrying out a fresh set of tests, but the 8500GT would more frequently lock-up without every completing a successful run. Previously this graphics card would work on Nouveau. It also continues working fine on the NVIDIA binary Linux driver.
GeForce 8600GT: The 8600GT was another 2007 product and it's based upon the G84 core running at 540MHz with 256MB of 1400MHz DDR3 video memory. The ASUS GeForce 8600GT 256MB graphics card is actively cooled.