I recently bought a notebook from HP, the HP 355 G2 with A8-6410 processor.
Inside there was a 4GB DDR3L-1600 Kingston memory module shipped, and there are two slots available.
I checked with CPU-Z and it showed a DRAM Frequency of 800MHz.
I added a 8GB DDR3L-1600 Cruical memory module to the second slot, and checked again with CPU-Z.
The DRAM Frequency was just 665.3MHz, the memory size of 12GB was recognized correctly.
I thought it must be because of two different modules, got for testing two other identical 4GB DDR3L-1600 Kingston memory modules, and DRAM Frequency was again just 665.3MHz.
And, if only one slot is used, with any DDR3L-1600 I had available, DRAM Frequency was 800MHz. But whenever both slots are used, it dropped to 665.3MHz.
What's wrong? Do I need some specific memory modules for this notebook, respectively CPU and memory controller?
HP Support suggested just that, but I believe it's not because of this. Perhaps the memory controller is working that way that it drops down to 665.3MHz if both slots are used. But why should that be? With none of my previous notebooks or pc this happened, always the memory speed as specified.
And Google says, that A8-6410 has a single-channel memory contoller for DDR3L-1866, which would be even faster, but instead it runs with 1333.
I use this notebook with Windows 8.1 Pro 64-bit, if it matters
This is a question you need to ask the laptop manufacturer.