For JEDEC spec (industry standard) memory modules (ValueRAM, Server Premier, non-overclock), mixing across banks is okay, but Kingston does not recommend mixing memory within the same bank group. Doing so on PCs/laptops disables channel architecture optimization, forcing the memory to perform at half the potential bandwidth. On some systems, mixing within a bank may even be disallowed by the manufacturer. On servers, mixing within a multi-channel bank group is not permitted. If adding memory to the second bank group, it is always recommended to put the higher capacity memory in the first bank. Mixing memory modules or kits in a PC/laptop using overclockable memory (Kingston FURY) is never supported.