RAM is one of the factors that determines how quickly an android headunit operates. More RAM means more apps or more of the app can be kept in RAM for quick access, say, for switching between navigation and streaming. More RAM means for a more fluid experience.
The early fakes had a miserly 1Gb of RAM, which, after android had used its share, this left only 762Mb for the user to load apps. The Chinese fakers edited the files that report the RAM level to show they had 2Gb RAM worth of chips fitted.
The PX6 processor can access a respectable 4Gb of RAM. This is it maximum addressable RAM. There may be less RAM fitted, but never more. 4Gb is the PX6 maximum RAM.
As newer processors are designed for android headunits, the designers include the ability to access more RAM, so the mainboard designers can specify a higher amount of RAM. The UIS7862 SoC can access a maximum 6Gb of RAM.
Extra RAM chips, DIMM slots, SODIMM RAM and DDR RAM are all often upgradable on a PC or laptop by removing the cover and operating a few clips. Removing the lower capacity RAM modules and replacing them with higher capacity RAM chips or filling an empty RAM slot with a stick of RAM are all options, but not for the android headunit.
Although the android headunit may look like a mini PC, it is much more akin to a phone. You can’t upgrade the RAM in your phone, you just buy a more modern phone when your current one gets ‘slow’.
There are no RAM upgrades for an android headunits and quite often the limit is the processor, but if not, there are no empty RAM slots waiting to be filled.