Does it hurt to use 1.35v and 1.5v RAM together?

[N.E.A]

A friend of mine is going to upgrade his current system's RAM. He currently has 8 GB RAM (2*4GB) running at 1.35 volts. His CPU is  i5 3550. 

 

The options available are running at 1.5v. So we were wondering if it would be ok to use 1.5v in his current setup. Also, does the CPU support RAMs running at 1.5v? 

 

The RAM setup he'll do will be as follows: 

 

Slot 1: 8GB DDR3 (1.5v)

Slot 2: 4GB DDR3 (1.35v)

Slot 3: 8GB DDR3 (1.5v)

Slot 4: 4GB DDR3 (1.35v)

 

Will that be ok or do we need to install each two identical sticks right next to each other?

[Fight Game]

I've done it without issues.  I can't say whether it's officially supported or anything like that, but it has worked for me on a few different occasions.

[wevsspot]

It would be helpful to know his motherboard DIMM slot configuration and speed/timings of the RAM he is considering and the RAM that he already has.

 

The voltage difference in and of itself probably won't be an issue because you should be able to tweak the DRAM voltage as needed to find a happy medium between the two that works just fine.

 

If the timings between the two different memory kits are significantly different that may add some level of complexity though.

 

It would probably also be a bit less complicated to set up if you kept the matching memory modules on the same memory channel, i.e.

 

Put the 1.35v memory in the DIMM slots for Channel A and the 1.5v memory in the DIMM slots for Channel B.

 

Even taking all of these precautions there is always a chance that it will work but it won't be stable.  Most MB manufacturer's recommend using identical memory modules if you are going to populate all of the slots.  That doesn't necessarily mean the exact same brands, but they do like you to keep the speed, timing, voltage specs. the same.

[ir_cow]

im pretty sure they all run at the same voltage, so either all 1.35 or all 1.5, etc. so mixing can cause problems at higher speeds

[Waco]

They'll all run at the highest voltage and the slowest timings of the entire set.  It's not ideal, but it should work just fine with 12 GB in each channel.