Why are there RAM chips with bus speed of 1600Mhz since there aren't CPUs that support more than 1333?

Question

It is not my profession but I think my question isn't that stupid :)

Intel i7-2600 supports RAM: DDR3 1066/1333 non ECC

Same for Xeon, Amd A4 & A6 and so forth..

Why are there RAM chips with bus speed of 1600Mhz?

Answer 1

1. Before memory controllers were integrated into the CPU, they actually operated at higher clock speeds. The CPU integrated ones are still faster overall, due to not having a delay between memory controller and CPU, but for those discrete memory controllers (north bridge of chipset), you'd want the higher RAM. It's somewhat ironic that you've tagged your question fsb and then mentioned the Core-i line and AMD APUs, none of which have a Front Side Bus.

2. The "supported" RAM speed of those CPUs is the officially supported speed. Overclocking is quite common.

3. Even when the RAM chip is used at a lower frequency, the higher-spec RAM chips will have fewer wait states between e.g. address stable until first data word read back. The clock speed controls the burst throughput within a RAM block. There are many many other timing factors affecting system performance than burst throughput.

Answer 2

Because they can be supported by faster buses, which will be able to operate the RAM at higher frequencies. Just because such chipsets don't exist now, we cannot infer that they will never exist. However, it's possible to use the RAM modules on existing systems with slower buses. This means that users can buy the RAM now to use on current chipsets, and when they upgrade to a faster bus speed the RAM will already be able to take advantage of it.

Whenever two things have to work together there's a chicken-and-egg problem associated with making improvements. Unless you can make both things better together (say you run a factory making both nuts and bolts), there will likely be times when one side of the operation has a technological lead over the other, but both need to have the improvement before anyone gets an advantage. If you support backwards compatibility, you can get your improved version straight out to market before the new supporting products are ready. Consider the related problem of broadcasting colour TV signals when everyone has a monochrome set, or selling colour TV sets when all the channels broadcast in monochrome.