Windows 7 Usage Of Ram And Limiting To Programs

my windows 7 has 4GBs of physical memory available tho it seems to often times only use about 3GB the thing is that as i use it, it will go above 3GB and then back down without me closing anything, what i figure its doing is limiting programs sense when this starts to happen programs like chrome will swap tabs to blank white pages and load up them vary slow, i assume this has be a memory restriction and it also makes alot of other programs tend open back up really slow and have random lag hick ups, thing is why won't windows just let them use the ram they need and fill the about 1GB ram i have left available ? also the resource manager says almost all the unused ram is on stand-by