If you are upgrading an old PC that has DDR3 1066/800 Mhz RAM slots on its motherboard and planning to upgrade, then you might not be able to find new RAM modules with that frequency.
Newer RAM modules available in the market will have higher frequency like 1333 Mhz and 1600Mhz.
So can you put a 1600 Mhz RAM module in a slot that supports only 1066/800 Mhz RAM modules.
Theoretically it is supposed to work. The RAM stick should simply run at the lower clock frequency.
However the answer is not that simple. There is no guarantee that it will work.
I recently upgraded my old pc which had a Gigabyte GA-G41MT-ES2L (rev. 1.0) motherboard. More details here:
As can be seen on the specs page, it supported only DDR3 1066/800 MHz memory modules.
1. 1600 Mhz RAM - Did not work
I installed a 1600 Mhz memory module, and it did not work.
The exact model was
Hynix 4GB PC3-12800 DDR3-1600MHz desktop 240-Pin DIMM RAM Memory Module Mfr P/N HMT451U6AFR8C-PB
The sticker on the module has the following printed on it:
Hynix / KOREA 05 4GB 1Rx8 PC3-12800U-11-12-A1 HMT451U6AFR8C-PB NO AA 1306
Its a single rank memory.
The number 12800 indicates that its a 1600 Mhz DIMM module. That number is usually indicated on a sticker on the RAM stick itsel or the case.
Divide the number by 8 to get the speed in Mhz.
May be the newest 1600 Mhz don't support running at lower clock speeds so they are less likely to work. The 1600 Mhz RAM can be identified by the number
2. 1333 Mhz RAM - Did Work
After that I purchased another memory module with 1333 Mhz frequency and put that and it WORKED!!.
The exact model is:
Hynix 1333Mhz Desktop PC RAM DDR3 4 GB (Dual Channel) PC (HMT351UCFR8C-H9 PC3 10600U)
The number 10600 indicates that its 1333 Mhz
So the answer is that 1600 Mhz memory modules may not work in a slot that supports only upto 1066 Mhz. However the 1333 Mhz RAM worked.
If higher frequency RAM modules are installed in lower frequency slots, their speed is stepped down to match that of the slot and the system uses them as usual.
But this does not happen always. If the RAM module does not support stepping down the frequency
So if you are planning to buy some RAM for your old PC, keep in mind that it might not work.
You are better off trying a 1333 Mhz RAM instead and it is more likely to work.
Though a 1600 Mhz RAM might work, but there is no guarantee.