I have a 2009 Macbook with 4 Gb of RAM, which I mostly use as a desktop with an extra keyboard and larger screen. It originally ran with Snow Leopard but I have upgraded, first to Mountain Lion and now El Capitan. The reason for each upgrade was that web browsing became impossible - Flash wouldn't run and many websites wouldn't load properly because my old Browsers had insecurities. But El Capitan often runs very slow. I don't use really memory hungry software - I normally have open Safari, Mail, an RSS reader (Vienna) and sometimes Libre Office or Gimp. But I assumed the occasional beachball spin was due to RAM shortage, so I have taken to keeping Activity Monitor open a lot. I have found that I rarely use a lot of the CPU, but the Ram generally runs with about 3-3.3 Gb of the 4 Gb RAM in use. I thought this would be sufficient pressure to make upgrading to 8 Gb RAM (at a cost of less than $100) a worthwhile investment, but I note that the Memory Pressure graph on Activity Monitor rarely gets out of the green, and even when I opened a whole bunch of other software, it only went to yellow, and never to red. So I'm wondering if anyone can advise me please, if I should believe the Memory pressure graph that my Ram is sufficient, or I should believe my own assessment that it's not? My options are to double the RAM now and hopefully extend the life of my ageing MacBook but another year or more, or buy a Mac Mini when new models are rumoured to be released early next year, but I don't want to buy the RAM if it will make little difference. Thanks for any ideas you can offer.