I have a MacMini which ran fine when purchased. When, however, I installed Yosemite 10.10.03/04, I began to notice Safari was slowing to an unbearable crawl. It is so bad I can sometimes sit, waiting over a minute for a sentence I have typed to appear letter....by....letter....by.....letter in a text input field. When it's reached this phenomenal speed I always have to restart the Mac. I decided to invest in some more RAM. This did not work, the same thing happens; within half and hour or so of browsing (obviously it is far worse if I have several tabs waiting to be read) the Mac starts to become unresponsive. A check on RAM use shows that Safari is swapping memory to/from the HDD after being open for 40-45 minutes. RAM pressure is still green but all my physical RAM has gone. Checking Memory usage shows most of the RAM has been absorbed by caching tabbed pages and those I have read and closed. Safari, itself, often consumes 3.5GB. I joined Apple Mac OS beta users in the hope a fix was one iteration away... It's not happened. I have never had a Mac OS this bad at memory usage. It was an advantage of Windows. Now I find myself turning more to Windows 8.1 with Safari and Firefox for internet use than my Mac. Sad state of affairs. Suggestions as to what could be wrong?