The system recognize less ram than i have

If you open a terminal, either from the program launcher, or with Ctrl+Alt+T,

what is the output of

uname -a
lsb_release -a

?

uname -a:

2.635-31 generic #63-Ubuntu SMP i686

No LSB avaliable

Desc: Ubuntu 10.10
releases 10.10
codename: maverick

Here you go

You are running a 32 bit version of ubuntu, for which the default kernel limits the addressable memory. It might be that you either (1) can use a "PAE" kernel to gain access to your extra RAM and then reboot to this new kernel, or (2) you *might* be able to reinstall a 64 bit version, which gets you all your ram.

Can you also provide

cat /proc/cpuinfo

?

Cpu is core i3-2100 3.10ghz

i dont get what uo mean by cat / proc /cpuinfo?

thanks

OK, well if you are sure that your CPU is an i3-2100, then I don't need the info from the "cat /proc/cpuinfo" command (I was referring to the info from the terminal, much as the first question).

To summarise, you are runing 32 bit ubuntu, which requires you to install a "PAE" kernel that can access larger quantities of ram. The instructions for installing it are here:
https://help.ubuntu.com/community/EnablingPAE

however, as you have not installed a 64 bit version of ubuntu, you are not quite using your chip's full capabilities, and will get a modest performance boost by reinstalling the 64 bit version of ubuntu, rather than the 32. To do this, you need to select the 64 bit (aka "amd64") ISO from the ubuntu download page.

Installing the PAE kernel is a quick fix, and will cost you a reboot. Reinstalling a 64 bit version of ubuntu will cost you a re-done full install.

P.S. I was able to tell what version of ubuntu you were using from the "uname -a" command, which said "i686", which is the 32 bit kernel, without PAE. If you were running a PAE kernel, the word "PAE" would have appeared up in the output. If you were running a 64 bit kernel, then this would also have altered the "uname -a" output.