Hello Vhaughn,

The OptiPlex 3020 supports up to 8 GB DDR3 memory in 2X4GB configuration and the supported memory speed is 1600MHz. It does not support 1866MHz. Below are the possible memory configurations,

8GB DDR3, 1600MHz, (2 x 4GB)
4GB DDR3, 1600MHz, (2 x 2GB)
4GB DDR3, 1600MHz, (1 x 4GB)
2GB DDR3, 1600MHz, (1 x 2GB)

Thank you for below, i almost purchase that sale. 1866 Mhz.

Anyhow,  can i use same specs even different brands?

hi i am in the same position i have an optiplex 3020 small form factor and i tried putting in 2x4gb corsair vengeance ram clocked at 1866 Mhz with i3-4150  but i just get a beeping sound and the pc wont boot up.

My research has found that it is the operating system that determines the maximum amount of Ram Memory that is allowable, not the computer.  

Example: Windows 7 Ultimate reports that 192GB is the max. Being limited to only two ram chips hampers that option.  I would need a tower server with a tray to achieve such numbers.  

Am I on the right track?

@I8UB4 

Not quite. The memory must also be acceptable to your system's motherboard and bios as well as the memory controller (usually integrated on the cpu chip).

For operating systems, most 64 bit systems will accept large memory amounts. But 32 bit OS systems won't use more than 3-4 GB, even if you have much more. It will be wasted unless you also use it for a ram drive, etc.

Thank You!

You can buy 1866Mhz RAM if you want, but these systems don't support more than 1600Mhz. It's ok though, usually there is a JEDEC specified timing for lower bus speeds like 1600Mhz and 1333Mhz programmed into the RAM.

Also, as to compatibility, you can head to ebay and grab some Hynix or Micron branded RAM, which is what I'm seeing most Dell's ship with, and it will most LIKELY be compatible.

Make sure to get Unregistered and non-ECC RAM. This is usually indicated by a "U" after the bus speed designation, such as PC3-12800U.

hello

i would like to know if i can upgrading  my i5 4590  processor to i7 on the dell 3020 dell 040ddp motherboard

thank you  

Hi @tolon,

https://www.dell.com/community/Optiplex-Desktops/Help-on-Optiplex-3020-maximum-CPU-capacity/td-p/6240006 

https://www.dell.com/community/Optiplex-Desktops/Dell-Optiplex-3020-mini-tower-CPU-upgrade/td-p/7549121 

https://www.dell.com/community/Optiplex-Desktops/what-is-the-best-processor-upgrade-for-a-dell-optiplex-3020/td-p/7558742 

And more recently:  https://www.dell.com/community/Optiplex-Desktops/Dell-3020-cpu-upgrade/td-p/7619866