Welcome to the Dell Community  @AntonisPella 

There is not much documentation on what the max memory would be???

But I did test the E6400 for a max memory of 8GB "2x4"

https://www.ebay.com/itm/Hynix-2GB-4GB-8GB-PC2-6400s-666-12-OEM-Laptop-Sodimm-Memory-RAM-DDR2-800MHz-USA/233339675536?hash=item365420e390%3Am%3AmHMDRrNuD9Jd8RlJ6_RYbMg&LH_BIN=1

As you can see I also tested the T9600 CPU.

Best regards and Marry Christmas,

U2

NOTE: Make sure to update the BIOS to"A34" before upgrading the Memory or CPU.

https://www.dell.com/support/home/us/en/19/drivers/driversdetails?driverid=j0n6y&oscode=wlh&productcode=latitude-e6400

Max is 8gb https://www.crucial.com/usa/en/compatible-upgrade-for/Dell/latitude-e6400

Don't forget the end of support for Windows 7 in 3 weeks. Time to replace the old e6400.

https://www.microsoft.com/en-us/windows/windows-7-end-of-life-support-information

Or just install W10 for free???

Regards,

U2

Or just install Linux Mint. I wish I'd done it years ago. Works way better than Win10

I've been using Mint XFCE on Dell's for years now, works a treat. Just stumbled across this seeing if I can upgrade the RAM in my e6400 from the 4Gb that's in it

The system will support up to 8G RAM.

https://www.crucial.com/compatible-upgrade-for/dell/latitude-e6400

Welcome to the Dell Community @DtuxComp 

Did you read my test results above???

Best regards,

U2

Thanks, yes I did, had a quick search round and it's not exactly cheap for DDR2 4Gb sticks now is it, considering I only paid about £60 GBP for the laptop it's on the way to that for the RAM upgrade so as it's running fine with 4Gb I might just put that towards a step up the Latitude ladder when I see another one going for a good price, such great hardware

Sorry for up old topic. I have E6400 with Phoenix BIOS and i want to upgrade RAM by maximum. Tell me please what BIOS i need, and where to check is my model can be upgrade till 8 or 6 Gb of RAM. AIDA show that on board intel gma 4500 mhd, so i if I understand correctly, can I increase the memory to 8 GB? And tell me if it would be better to leave Windows 7 for better performance?

Regarding this i have similar query , does it only support ddr2 or can it be upgraded to a higher verison ????