Intel’s sixth generation processor officially supports DDR3L and DDR4 RAM; however, Skylake motherboards have also been listing support for DDR3 RAM. While it is possible to use DDR3 RAM with the new processors, this shouldn’t be done as it turns out the higher voltage requirements could damage the integrated memory controller (IMC).
DDR4 has a default supply voltage of 1.2V, while DDR3L defaults to 1.35V. On the other hand, DDR3 has a default supply voltage of anywhere between 1.5-1.65V. Tom’s Hardware spoke with Intel and discovered that this difference is power supply could potentially result in the IMC being burnt out, and subsequently also damaging the processor itself.
This issue is a concern for those who intend to build their own systems, as motherboard OEMs are currently stating that boards with the new LGA1151 socket are capable of supporting DDR3. Which is entirely true, but does not mention that Skylake itself does not play well with the older RAM.
It should be pointed out that it still is possible to use DDR3 RAM with Skylake by reducing the supply voltage. This will result in low clockspeeds, but will preserve the IMC. It is not an ideal arrangement, but one that can be achieved if the situation calls for it.
[Source: Tom’s Hardware]