How to improve old, slow iMac -- new SSD? Or more RAM? I have an old iMac for the kids: iMac 8,1 Core2 Duo with 3GB (2+1) RAM that was recently upgraded it to Mavericks 10.9



It's running quite slow; free RAM is always pretty low. Apps run "OK" once open; it's mainly switching between apps, loading apps, and booting up which take forever.

My question is how can I know if installing a 120 GB SSD (lying around) likely give me significant performance boost or if instead I need to upgrade RAM (which will cost me)?

I replaced with SSD -- seems faster -- but follow up here: Best version of OSX for 2008 iMac?
According to your comment, it looks as if you could do better with more RAM. If it was just launching slowly, then I would say the SSD, but since its switching apps also, I think more RAM would be nice. Unless your iMac ran a lot better under Mountain Lion or below, I really wouldn't downgrade.

BTW: Don't disable the user accounts. Just log off when you are not using that user account.

Since you have a spare SSD, you could also just connect it externally using an inexpensive USB to SATA adapter and install new OS on it and run some A/B tests. You won't see the full speed of an internal placement - especially if you use USB 2.0, but it's often enough to know rule out RAM or OS as a cause of slowness.