In an earlier post, CA_Steve suggested that I look at 1.35 Volt DIMMs instead of 1.5 Volt. This got me thinking about the heat of DIMMs, which had not even occurred to me before. I suspect the heat from DIMMs would be small, but since I am buying new anyway, I might as well get the better option.

There are 1.35 volt DIMMs available for about 20% higher price. I thought however that it would probably be better to switch from the 4x4 GB I was planning on to 2x8 GB. Even if the two 8 GB DIMMs are 1.5v, they should take less power and thus give less heat than four 4 GB DIMMs at 1.35v.

Most 8 GB DIMMs use a 10-10-10-27 timing instead of the 9-9-9-24 timing that seems standard with 4 GB DIMMs. I am not sure if the slower timings would have much real-world affect. With all the other bottlenecks in the system, even with a fast CPU with 8 MB of level 3 cache and an SSD drive, I suspect there would be less than a 1% difference, but that's only my wild guess.

From some Google searches I see that having 4 DIMMs may limit your overclocking potential. I will never overclock this computer so that is irrelevant for me, but that might be important to someone else.

Also from Google, it appears that in the past, having all DIMM slots filled could increase the chances of motherboard instability, although that seemed restricted to CPUs prior to Sandy/Ivy bridge, and maybe also restricted to overclocking scenarios.

It seems obvious that 2 DIMMs, spaced apart, would cool more easily than 4 DIMMs packed together, due to increased air flow. Since my motherboard (Asus P8Z77-M PRO) has a small gap between the second and third slots, that may be less significant in this case. Some motherboards have them all squished together.


Is there any reason that four 1.35v DIMMs is preferable to two 1.5v DIMMs, or vice versa? Would the CL10 versus CL9 timings have more than a slight effect?

Thanks guys.

Unless thre is some obscure compatibility issue for your motherboard, go with 2x8Gb.

Memory isn't a significant source of heat anyway, so unless seriously power-limited, I wouldn't opt for the 1.35v, which probably makes less of a difference than whether you run a screensaver or blank screen. If you're set on it, though, go 2x8gb if you can afford it - always better to leave room on the off-chance 16gb isn't enough in the future.

Crucial Ballistix Sport 8GB is 9-9-9-24 and low profile. Also quite affordable in my area. They are 1.5v though, but there's also a "very low profile" version that's 1.35v. They are probably more expensive though.

As suggested by the others in this thread, I would check motherboard compatibility lists for the sticks (or just 8 GB ones in general, if your preferred model isn't there). Googling your planned component combination is another way to explore compatibility, as you've already done.

Motherboard and RAM stick compatibility is still an issue today, and it's an annoying, sneaky one. Loading all 4 slots I don't think is wise, it puts more power strain on the motherboard, and previous controllers at least have indeed had stability issues with 4 vs 2 sticks. Unless we're talking heavy overclocking, the speeds aren't massively important (CL9/1600 is typical for 4 GB), but at low performance levels it might be the last straw. As Vicotnik pointed out, there are options, so I don't think you should settle for CL10 or sub-1600 speeds (check review sites like X-Bit Labs or Techpowerup for analysis).

As regards to heat production: if the maximum operating power of a component is 2-3 W (check specs, e.g. http://www.kingston.com/datasheets/KHX1 ... 3B1_8G.pdf), it's very unlikely it'll influence a standard or even low-airflow system's heat balance or overheat itself.

The main question about low-voltage sticks I would think is "why not"? It obviously takes a higher grade of components and/or design to be able to operate at lower voltages, and throwing in extra voltage without overclocking is just pointless waste. So: why would you NOT want a low-voltage stick? A 20% price premium might be steep in principle, but if we're talking $25 vs $30... I would pay the $5 for better components (and thus an improved world, if you're a tech-hippie(?) like me).

PS. My personal favourite is G.Skill RAM, found good specs and recognised design for decent prices. Below is a price comparison from today.