My computer is getting old (almost 6 years old I think) and is becoming increasingly slow. The past few week were pretty bad and I am now realizing that my computer is continuously short on physical memory. Here is a screenshot of the memory activity showing that 3.98GB out of my 4GB of physical memory are used.
This screenshot was taken while I was using my computer as I usually do, not very intensively. I had 2 Safari windows open (gmail and StackExchange), I had two .txt files of about 10kb each opened with Sublime Text 2 and had the R (programming language) console opened but nothing really heavy was running and no particularly big objects were stored. I had 4 terminal (Bash) windows open to manipulate files and some ssh connections but nothing was running at the moment of the screenshot. I also had a 328kb pdf was open in Preview.
Safari is taking much memory (at least more than what I would expect), so I switched to Google Chrome (but Google Chrome is known for taking much CPU) and to Firefox but the problem was not persisted.
Are those applications taking too much memory? If yes, how can I solve this issue? Am I just overestimating the capacities of my computer (but I felt like I didn't such issues before)?
FYI: My machine is a MacBook Pro running on OSX Yosemite (10.10.2) and here are some other screenshot in case it helps!