iMac 20-Inch "Core 2 Duo" 2.4 (Early 2008) Specs (Early 2008, MB323LL/A, iMac8,1, A1224, 2210): EveryMac.com
hello all can i ask you think that this old imac can be used for internet browsing facebook youtube in 1080p ?
and for a movies to watch
I have, right in front of me as I type this, a 2007 20-inch iMac. So I have a lot of experience with old iMacs.
My old iMac runs great, with good speed. You can't expand memory beyond 6GB, but I've never even felt the need to expand beyond the OEM 4GB.
Specs for yours:
http://madeapple.com/imac-20-inch-early-2008/
You can upgrade as far as Mac OS 10.11: "El Capitan". However, if you upgrade beyond Mac OS 10.6 "Snow Leopard", you will lose all of your PowerPC-based software. I've chosen to stick with Snow Leopard for my old iMac, as Snow Leopard was a supremely stable OS. (Of course, I have a lot of legacy software that is PowerPC that was never updated. That's why I maintain this old iMac in my office.)
The downside of sticking with Snow Leopard is that Safari is tied to the OS version, and that version of Safari is just about unusable now. The good news is that you can get an older version of Firefox that will run great and which is mostly modern:
Firefox (48.0.2) (free)
was the last version of Firefox that runs under OS X 10.6. It's an excellent choice. You can surf the Web, view YouTube videos, etc. nicely with it. Facebook, however, will not work. I don't know how high you would have to go, as far as upgrading your OS, to get Facebook to work.