8gigs of RAM :) ? in my experience not a single byte over 4GB RAM matters in linux desktop. I have (Ubuntu 13.10 on an old sonny vaio core 2 duo) 4GB and with all the workspace open and a virtual box with 1.5GB RAM allocated to it, i didn't reach 3GB (it stays around 2.7-2.8GB).
I have 16GB. And I have managed to use all of that, with a combination of calligra + blender + around 5 vms in virtualbox + 3 containers + background compiler update operations + 3 web browsers open all with a total of around 100 tabs at the same time.
I find it is just quality of life. If I use 4gigs, I can only have 2 real memory intensive applications open at the same time. If I had 8+, I could easily have anything I want open in normal usage and not break a sweat.
It sounds like you might be using a 32 bit version, which will not utilize more than 4GB of RAM. 64 bit versions have the ability to address memory beyond the 4GB limit of 32 bit systems.
With 32 bit versions of Linux the kernel is mapped into the upper 1GB of address space, and then whatever is left over from the remaining 4GB is exposed for general purpose use, and made visible to the user. The means that by default, even if you have 4GB of RAM, you'll never actually see anything more than 3GB exposed for your use, because the kernel has already reserved 1GB of RAM for itself. (these ratios change proportionately, when less than 4GB of RAM is present)
It's also possible that your system is hitting the 3GB mark and then paging virtual memory to your swap partition.
This makes me hopeful for my future. I have 4GB and am in the constant cycle of "close firefox so I can start my VM, close the VM so I can start Inkscape (with a big file), close inkscape so I can start firefox, and if you want to play one of these new GNU/Linux games: _close_ _everything_".
It honestly feels like there is some kind of problem with the system swapping (or failing to swap some memory) or some memory leak that I can't quite track down. Maybe something got fixed somewhere in the last two years...
But it opens new options. For instance you can mount /tmp as a tmpfs (in memory) file system and spare some write cycles from an SSD. Also, the system uses it as cache, which is nice.
