In particular, Mac OS X don't even run well with only 4GB of RAM anymore, and older machines use DDR2 where 4GB SO-DIMMs (and any other sticks based on 2Gbit DDR2) are rare and expensive. I wonder what is the current status of this bug BTW: http://apple.stackexchange.com/questions/42426/can-i-upgrade...
> In particular, Mac OS X don't even run well with only 4GB of RAM anymore
It actually runs great. I'm using a 2011 Air w/2GB (cheapest back then) and El Capitan and it's almost as fast as my 24GB Mac Pro.
I push it a bit with Logic Pro X + drum samples (for my V-Drums), but it handles that without complaints. But for web, videos and programming there isn't much of a difference.
Mavericks introduced RAM compression, so for RAM-constrained machines it may be even better than the previous OS.