How !?
I have Macbook late 2008, Intel SSD, 8 GB RAM, was super fast on Mavericks. And now on Yosemite, it's so slow. Before it was faster even with its 2 cores than MacMini 2011 with 4 cores, now the Mac mini is faster with its HD.
I don't know what to do.
There are no processes really in the background using CPU, it just takes so long for everything - sort files in Finder, open a jpg in Preview..even "Open As..." takes sometimes 10 seconds to show up the list of available programs.
Its almost equally slow no matter if Ai, Ps, Word4Mac, Pages, Sublime, Safari and Chrome + other utilities open, or no programs at all.
I do Repairs Perms regularly..I had a problem with SSD-file system though, 'cos one RAM block stopped working properly and processes crashed all the time, probably a Disk writing process too.
However, I did Repair Disk and now its reported as "all is fine", and put a new Corsair RAM, memory tests confirmed it as ok.
It's a disaster. I was thinking could it be its so bad because of only 2 cores, but now as you say its great on your Yosemite, i don't know why.
Looking at the processes there 212 processes incl. 4 started by me.