I tested much GPUs with free software (only). All >> "ALL" ! AMD/ATI GPUs
need non-free firmware data blob, it is not an runnable, just data, but
trully non-free. This blob is about 2kb or about 70 lines of hex code in old
graphics cards, today (for new cards) is about 500kb or even more, it is much
harder to try reverse engineer it. Some (mostly) old ATI cards can work
(really NOT well) without that blob, but forget about 3d (even 2d)
acceleration, I can say that it is almost not usable without that blob, and
some ATI/AMD card will not show/detect the right monitor's EDID and
resolution. So if you try to use AMD/ATI card without a proper blob (all
blobs included in standard non-free linux in /lib/firmware/radeon/, obviously
you will not find those in linux-libre or one deblobbed linux), the main
processor(CPU) will do all software rendering (for 2d for example), and it is
a bit slow and buggy), very unpleasant. AMD/ATI GPUs can not to work properly
without this blob, just forget those GPUs forever if you want use a computer
with free software only. Also some chips can overheat if here is no blob
loaded.
For NVIDIA card you will have no problems. Non-free blob (microcode-firmware
as in ATI/AMD GPUs) is burned into SPI flash or rom-epprom memory, which is
soldered on the GPU itself (no need non-free microcode-firmware in your OS,
outside of GPU). You will have no automatic reclock* for 2d/3d rendering, so
your GPUs will run idle core and memory clocks. YOU CAN DO manual reclock
(core and memory) for KEPLER (example: gt730,gtx770,gtx780ti), and probably
MAXWELL v1 (example: gtx750ti), you will get a decent 3d performance. For
more info ask in IRC #nouveau channel, they always stay with updated info.
I don't know, because I did not tested and do not have: probably old Voodoo
and Banshee will work fine, I don't know. It is too ancient GPUs for too
ancient hardware, with a few (8-16mb) of memory. Forget ancient Matrox or
SiS, they run non-free and never supported GNULinux.
The best and stong performace you can get without running non-free is Intel
integrated GPUs. I did not tested latest Skylake and Kabylake hardware, I do
not know if those need for some non-free microcode. But previous generations
you can get something strong as HD4000 or even better, some Intel Iris
integrated GPU.
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reclock: get you video card to run high core and memory frequencies for 2d/3d
performance, Nvidia drivers will do it automatically when any software
demanding it. Do not confuse with downclock or overclock. Reclock is
something basic in all GPUs.
