I have a mid-2012 MBP, 4GB RAM and 500GB HDD. I've upgraded to Yosemite when it first came out and since then this machine has been struggling. I didn't get around to post about my issue earlier, but I don't remember noticing this on Mavericks. Currently I'm on 10.10.2 After browsing for a while on Safari, few different sites, around 4-5 tabs open, Safari uses almost all the available RAM in the system. I start noticing the sluggishness after a couple of hours, as the RAM usage accumulates. The RAM usage causes the whole system to become really slow, I get the spinning color wheel whenever I open a new tab, change song on iTunes, etc. Sometimes when I'm typing something even the keyboard becomes unresponsive for a few seconds, the color wheel comes up and the keyboard won't accept any inputs, then suddenly enter all the characters I typed about 10 seconds late. The RAM indicator stays green the whole time, and I know everyone says if it's green it's fine, Yosemite will handle RAM management, but seriously, something is not right. It is not normal that a machine can come to a halt by only using Safari. Restarting Safari empties the RAM it was using and the system speeds up again, but until I restart I can still feel a small lag. Then after restart it happens again and again whatever I do on Safari. I made a screenshot of the Activity Monitor. I use this laptop for Safari, iTunes, word processing and in really rare cases I might edit 1 or 2 photos in iPhotos. I think it's supposed to be able to handle this even with this amount of RAM and an HDD. It seems to me that Safari is not doing what it should with the cached stuff.