max memory i can do in Dell Inspiron 5423 intel-core i5

8G max (2X4) - DDR3 or DDR3L, PC3-12800.

www.crucial.com has guaranteed to work memory.

Hi forcedgol,

It looks like ejn63 answered this (great answer!), I just thought I would add another option is to buy a matching stick of Samsung memory to complete the 4gb that is already in there. Doing a Google search on: m471b5273dho-ck0 turns up the matching set of memory for your system (make sure to purchase from a good vendor, if it's not from Dell directly etc.). And also, Crucial is great in my personal experience (and suggested from ejn63), I just recommend changing out the original stick so it matches in a pair if you do go that route. I mean I am sure it would work non-matching, it just is typically best to stay with the same model in pairs.

Here is a link to the Owner's Manual on how to change the memory.

Best regards,

Brad 

Depending on price is what I would go with (so the lower priced one etc.). The reason for this is because the memory will not run any faster than 1600 in that system (at least from the specs I have seen), so unless you plan on using the 1866 in another system later on it will be not be useful. Also, while the 1866 is rated higher/better it will not show in real world performance, and this is even if the system were to somehow run it at the higher 1866 (at least in my experience, aside from benchmarks).

I hope this helps, and regardless both are good choices.

Best regards,

Brad