I would never run a Mac under 8GB RAM these days. Even if you're a light user. Also keep in mind that you can never upgrade it.
Geez...I think (almost) everyone here is misinforming the original poster completely - neteng101 excepted, you've got it right.
OSX reports inactive memory (this is memory the system uses to cache inactive processes and frequently used apps not currently open) as "used" memory and this is in most cases the vast majority of what OSX is reporting as used memory. I would like you all to humour me and please try this experiment to prove what I am saying:
Close all applications. Go into the console and purge the memory (how to
here) and then restart your music streaming apps you mentioned and Safari with your two tabs or whatever. Then run Activity monitor again. I think you'll find that your reported used memory is much lower.
What you've done is purge the inactive RAM. That's it. Now your old closed apps and stuff have been thrown out of RAM storage and will have to load up from the HD or SSD the next time you use them.
I think you'll find that most of you had absolutely no need whatsoever to upgrade the RAM in your machines. If you are not seeing any performance problems, why do you think you need more RAM? I have been using the 2011 Macbook Air in my signature below to run a Windows 7 Ultimate x64 Virtual Machine with 1GB RAM allocated to it in parallel with OSX for work purposes for over two years and have had zero problems with RAM overloading or excessive paging out to the SSD, and this with up to 15 individual apps running over both OS's simultaneously, multiple large, complex and linked Excel, PowerPoint, Numbers and Keynote docs open, 10 tabs in Safari, and heavy accounting and finance software running in the VM. Sure I started to see excessive page outs at times, but with the fast SSD, I have been able to live with that, and have been extremely impressed with the performance of this little machine as my sole true laptop. It has gotten even better with Mavericks new memory compression features. In my use case, I have seen a noticeable performance boost with 10.9.
That's the big reason to upgrade the RAM, when you start seeing excessive paging out to virtual memory on the HD or SSD. Paging in is totally fine however. Here's a quick definition of page in and page out: (from a this
thread in Apple's own support forums)
If an application calls a page and it is in RAM, then a "page in" occurs. If an app calls for a page from memory, and that page is currently stored on the hard disk and has to be read back into RAM, then a "page Out" occurs.
So you see - 4GB RAM will still get you a lot further than you think, especially with the latest OSX Mavericks installed...
That said, if it were me, for the $200 extra, I would definitely get the mid-ranged machine with double the RAM and double the SSD storage.
😉 