Only 2.5 Go RAM

Best answer selected by MickaelL.

Ok thank you. I am reassured, and understand better now.

no problem for the 64bits version. I used it everyday for personnal use on the same computer  
It's just that i need a 32 bits version for work too.

thanks a lot for the speed !

That is your problem !! 32 bit operating systems can only use 4GB TOTAL of RAM -- this includes the RAM set aside for your System (usually 512MB or .5GB) the amount set aside for the video subsystem or video page files (usually 256 - 512MB per display\video card installed) and any reserved for sharing with the video card chipset if using onboard video and not a dedicated video card ( another 512MB to 1GB. depending on the chipset)

From your description you are using the onboard video chipset with 512MB reserved and the other 1GB is being used by the system reserve and video page files leaving you approx 2.5GB remaining thus the system is showing things correctly -- Installing any more than 4GB in a 32 bit operating system is just wasting any above that since the memory is mapped into a 32 bit storage space meaning only 32 bits of addresses can be used (32 bits = 4,294,967,296 locations or 4096MBs (4GBs) worth of addressable memory)

The only way to address more would be to switch to a 64 bit OS which stores the memory mapping in a 64 bit space. HERE is a good article that explains things in more detail if you want to read up on it !

Unless you are running a x16 bit program, there is no reason you 'need' the 32 bit OS.