I have an E-510 and was thinking about moving over from Windows 7 x86 to Windows 7 x64. Dell.com says that my system has a max ram of 4gb, as do several other memory companies. The Crucial website, however, says it supports 8gb.
I have all 4 slots filled in my E510. Originally came with 1GB but decided to upgrade and got a great deal on 2 x 2Gb. After I upgraded I just left the old 2 x 512 Mb pieces in there ... 2 x 2Gb + 2 x 512Mb for a total of 5Gb. The bios definitely recognizes it. Have not upgraded yet to 64 bit OS so I can't say for sure that it works...but the BIOS handles it properly so I am assuming it will.
I have a Dell GX620/GX280, it's not the exact same motherboard, but it's nearly identical, and supports 8GB. Nonetheless, it'd be a good idea to update the BIOS to the latest release if you haven't done so already.
Just for reference, if you do decide to buy 4x 2GB modules, please post back here and let us know if it was recognized by your BIOS. It will help others with the same question.
EDIT: Rockyjohn's link (below) is an interesting article, and anyone planning to reinstall their OS just for more RAM should indeed consider whether it's ultimately worth it.
Message edited by techshui on 11-16-2009 at 11:29:36 PM
Although before you spend a lot of money on more memory, you might want to read this THG article that states that very few programs can even take advantage of 3 GB of memory - even with multi-tasking.