I just need to make it clear by asking you all a question

[Mikulas]

Does cpu have some support of max ram ?

I want to upgrade my 3gb ram to 4gb.

my motherboard is ASUS P5KPL 

and my CPU is Intel core 2 duo e4600 2.4 GHz

I need to know

[AlHill]

Your 14 year old processor did not have a memory controller.

https://ark.intel.com/content/www/us/en/ark/products/32242/intel-core-2-duo-processor-e4600-2m-cache-2-40-ghz-800-mhz-fsb.html

So, it is your motherboard that you need to check.  I did, and it is 4GB max:

https://origin-www.asus.com/Motherboards/P5KPL/specifications/

The motherboard uses the G31 chipset:

https://ark.intel.com/content/www/us/en/ark/products/31913/intel-82g31-graphics-and-memory-controller.html

However, it depends also on your OS.  Read carefully the paragraph on memory.

Doc (not an Intel employee or contractor)