With Skylake hitting the market, and hopefully selling in vast quantities, Intel is cautioning system builders users not to use old memory DIMMs, even if OEMs are saying its ok.
Skylake is the first CPU generation to support DDR4, which I have maintained is kind of pointless for the majority of users because its speed improvements are negligible as is the drop in power. Intel said it would support both DDR3 and DDR4 on the Skylake platform, but there are multiple forms of DDR3 and you have to be careful.
Skylake's integrated memory controller (IMC) officially supports only DDR3L with a voltage of 1.35 volts. Standard DDR3 runs at 1.5 volts, and some go as high as 1.65 volts. The DDR4 standard voltage is 1.2 volts. By running memory at a higher voltage, you run the risk of burning out the IMC and since it's a part of the processor, that will kill the whole processor.
The propellerheads over at Tom's Hardware Guide were the first to point out that major motherboard OEMs have listed support for non-DDR3L RAM on their boards. Gigabyte is claiming support for DDR3 at 1.5 volts while Asus and ASRock are claiming support for DDR3 at 1.5 to 1.65 volts.
That's just plain wrong. An Intel spokesman told me clearly that Skylake does not support DDR3 or DDR3L at 1.5 volts. It only supports DDR3L at 1.35 volts and DDR4 at 1.2 volts, period, end of story. It's not like your computer will blow up when you turn it on but over time there is the risk of burning out the CPU, so why risk it?
System builders often reuse parts and I'm certainly one of them. When I migrated from the Sandy Lake generation to Haswell, I reused my RAM (and hard drives, and GPU, and sound card) because it was certified on the new platform. So this is a real gotcha for people who like to build their own PCs. Intel is abundantly clear but the OEMs are throwing people off. Given they are all in China, I suspect something got lost in translation. So I'm checking with them.
Tom's made another find. The IMC supports memory speeds of "only" 4,133 MHz. I say only because while the bulk of DDR4 DIMMs on the market 2,133 MHz and 3,000 MHz, at least one RAM company has broken the 4,000 MHz barrier. As they noted, memory over 4,000 Mhz is more prone to errors, so why risk it?
So, if you choose to go with DDR3 for your new Skylake machine, make sure it is DDR3L at 1.35 volts. But judging by what I've seen in stores, Skylake will be overwhelmingly DDR4, and a quick check of prices on NewEgg shows that DDR4 DIMMs have come down to parity with their DDR3L counterparts at the same capacity.