Optiplex 790 - 1333 or 1600MHz memory?

BTW: You didn't say which form factor 790 you have.

The Desktop, Mini-Tower, and Small Form Factor can handle up to 16-GB of RAM, but the Ultra Small Form Factor can only handle 8-GB.

Looks like you'll have 12-GB which should work, unless you have the Ultra Small...

With the old 1333MHz RAM installed, the new 1600 MHz RAM will clock down to the slower speed.

If the chipset and BIOS can handle the higher speed, the new RAM will run at 1600 MHz, but only if you remove the old, slower RAM.

And Crucial will take their RAM back if it doesn't work, so nothing to lose. :emotion-5:

Technically you should be fine.  The ram controller will slow down the 1600Mhz memory to the slowest on the board and since you have 2 sticks of 1333, the 1600 will slow down to 1333. 

Technically you should be fine.  The ram controller will slow down the 1600Mhz memory to the slowest on the board and since you have 2 sticks of 1333, the 1600 will slow down to 1333.

I typed faster than you, but at least we gave him the same answer! :emotion-4:

Thanks guys.

I have the desktop.  16MB max.  

How do I check to see if the BIOS and chipset will handle the extra speed?  The chipset is supposed to be Q65, and this website says the i5 2400 takes the DDR3-1066/1333.

http://www.youcpu.com/en/cpu/Intel-Core-i5-2400-6M-Cache-up-to-3.40-GHz 

Hi,

Thank you for writing to the Dell Community Forum. 

The OptiPlex 790 system supports up to 16 GB of memory in the mini-tower (MT), desktop (DT), and small form factor (SFF) chassis with 64-bit operating system. The maximum memory supported in the ultra-small form factor (USFF) is 8GB. The memory speed supported is 1333MHz DDR3 memory. The speed would be step down to 1333Mhz even if use the 1600Mhz memory. 

Memory modules should be installed in pairs of matched memory size, speed, and technology. If the memory modules are not installed in matched pairs, the computer will continue to operate, but with a slight reduction in performance. Since you are installing the memories in pairs, you should not have any issues and the system would work fine. 

How do I check to see if the BIOS and chipset will handle the extra speed?

Easier to pull out the old RAM and install the new RAM in those same two slots and then see what speed is reported by a free app like CPU-Z or Speccy. 

Note that they report speed of dual channel RAM so you have to double the number reported. If it says 800 MHz, that would be 1600 MHz dual channel RAM.

EDIT: But keep in mind, unless you plan to completely replace the old RAM, the new RAM will only run at the speed of the slower RAM.