[1] You could have 20GB of hard disk space free, but use XCode, Firefox and a few other apps, and soon you're down to 10MB and you get the dreaded "Your Mac is running out of disk space" dialog and you have to force quit all your apps, and type "purge" into a Terminal in a desperate attempt to get the swap released...
"purge" doesn't touch swap, it discards disk cache. Its use (according to the man page) is to simulate cold boot disk performance. The command has no use for memory management, because disk cache is automatically discarded when free memory runs out.
http://workstuff.tumblr.com/post/20464780085/something-is-de...
It's a real tangible performance boost though. Feels extremely snappy on my Retina Macbook Pro. Scrolling is faster and I went from 2,5 hours of battery life to 4,5 !
The new way Multi Display works is also much better than the old way, Full Screen Mode is actually really useful now.
E: Oh, looks like it's already there in waiting: http://new.roaringapps.com/
What do people on HN recommend? Using this technique to do a complete reinstall, or upgrading?
With that said, as a developer sometimes it can be handy to do a clean install. For example, if you have any custom kernel modules, these will certainly be blown away in an upgrade. Additionally, developer tools installed in /usr/ can be interfered with, and in general the probability that something will be incompatible/broken is a bit higher.
So be careful anyway.
That said, you can definitely chain update your way from 10.4 to 10.8 without issue, and similarly from 10.1 to 10.5. The latter case is a little tricky as many of the machines that ran 10.1 were not deemed fit for 10.5 (e.g. the G4 Cube variants), but there are workarounds.
Probably get a solid and consistent extra hour. From 6 solid hours to 7. I can push to 9 now if I lower the brightness and don't browse the web.
The most common solution to this problem is to use tmux or screen, or just disable sleep.
However, apart from that I'm getting longer battery life (from ~3 hours up to ~4.5 hours) and I like the OS. I guess bugs as the above are normal with OSX point releases. I still remember the pain when I ran Leopard.
Open the .dmg, drag the install .app into /Applications and run it from there. The upgrade works fine.
And honestly I'm not really sure that a feature that is memory hungry is really useful anyways, especially at that scale. At that point I feel it's all about the planned obsolescence, they just make algorithms that require to buy more hardware.
In that case software performance would only apply because of bigger hardware, not better programming. I'm sorry but with the computers of today, I really doubt programmers can invent resource hungry features that are really useful, maybe they can just do sloppy programming that requires more memory.
I've got a 2008 iMac 2.8 dual-core that I thought was getting pretty long in the tooth, but I'm thinking it's just the 4GB ram that's holding it back now. I can't add any more RAM and Mountain Lion just draaaggggss on it.
I bought a 4 GB DDR2 DIMM for my Dad's mid 2007 iMac, installed it together with a 2 GB DIMM and it has been running non-stop for almost a year now, without any problems. DDR2 is now a bit expensive, due to being old, the 4 GB DIMM cost me around 50$ on eBay.
If I go to 10.9 I'll definitely up the RAM.