I have a problem with Ubuntu 12.04 64-bit installed on Acer Aspire AO 722 with AMD C-60 processor. at the first startup, Ubuntu is much more resource consuming up to 500MB with Unity 3D. after I checked, was the most resource consuming is Xorg and Compiz. is it normal? My comparison with the Intel Atom netbook 32-bit consuming resource only up to 190mb with Unity 3D. any solution for that?
Your netbook with "Intel Atom" is 32bit and your "Acer Aspire AO 722 with AMD C-60 processor" is a 64bit processor, running Ubuntu 12.04 64bit. So, the simple answer is Yes, It is normal to use more resource for a 64 bit OS, than a 32bit OS.
As for comparison, I run Ubuntu 12.04 32bit with Unity 3D. It consumes around 350~ MB of RAM.
My Suggestion:
Though, You did not mention how much RAM you have, I will suggest to use 64bit Ubuntu with Unity 3D, If you have have >= 2GB and You are not a power user with graphics intensive work. But If you do lots of graphics intensive work, and have RAM less than 2GB, I recommend to use either Unity 2D or Xubuntu or Lubuntu.
For a detailed discussion about 32bit and 64bit, you can check this question
You can also read this page for a neat discussion about 32 bit and 64 bit system
When I run Unity 3D, it does not comsume as much resources that you are reporting. Do you know how to locate your system log files? Check and see if there are any errors.
Also, Compiz is stable, but not too stable. Memory leaks happen every once in a while, so try rebooting and see if you get the same amount of resources being used.
And finally, if you can stand not having eye candy and visual effects, you can just run Unity 2D instead. To do this, click the button to the top right of your login name box when you are at the Login screen, and then choose Ubuntu 2D.
Full fledged Ubuntu with Unity 3D will certainly eat more RAM, though I don't really know exactly how much is normal. I'm running 32-bit Lubuntu 12.04 on an Acer Aspire D257 and it uses 90 Mb of RAM without other processes going.
I think, most of the modern OSes are made for computers that have 2 GB of RAM or more, in my experience.
If you don't have that much RAM, I suggest you try Lubuntu, which is very lightweight. Or if you plan to buy RAM soon, you can use Unity 2D until then (which is usually more lightweight than full 3D Unity).
Since you already have Ubuntu installed, you can run it like a Lubuntu system by installing the lubuntu-desktop package. Then log out (or reboot, but that's not necessary), click the Ubuntu logo icon on the login screen, select Lubuntu from the drop-down menu, and log in.
