Hi everyone,
I installed Ubuntu 12.10 Gnome Remix on my new laptop but I've a problem with memory.
My laptop has 4 GB memory but Ubuntu recognize only 2,4 GB.
Obviously both BIOS and Windows 8 recognize all 4GB.

My laptop configuration:
Lenovo B590
CPU: Intel Core i5-3210M
Ram: 4 GB DDR3-SDRAM
Chipset motherboard: Intel HM77 Express
Integrated graphics: HD Graphics 4000.
Operating System: Ubuntu 12.10
Kernel: Linux 3.5.0-17-generic (x86_64)


Some useful command outputs:
Code:
dmidecode --type memory

	Array Handle: 0x000B
	Error Information Handle: Not Provided
	Total Width: 64 bits
	Data Width: 64 bits
	Size: 4096 MB
	Form Factor: SODIMM
	Set: None
	Locator: ChannelB-DIMM0
	Bank Locator: BANK 2
	Type: DDR3
	Type Detail: Synchronous
	Speed: 1600 MHz
	Manufacturer: Hynix/Hyundai
	Serial Number: 1A21B5B9
	Asset Tag: 9876543210
	Part Number: HMT351S6EFR8C-PB  
	Rank: Unknown
	Configured Clock Speed: 1600 MHz

Code:
free -m

                   total       used       free     shared    buffers     cached
Mem:          2483       1136       1346          0         56        515
-/+ buffers/cache:        563       1919
Swap:         4884          0       4884

Code:
cat /proc/meminfo | grep "Mem*"

MemTotal:        2542664 kB
MemFree:         1373552 kB
Also running live version of Ubuntu the memory is always only 2,4GB.

Can someone help me?
Thanks a lot.