# Which cache type is better for bus watching?

I am studying for an exam about memory (mostly cache) and I ran across a multiple-choice question from a few years back:

Which cache type is recommended for bus watching and is also used in multiprocessor systems?

a. write-through cache
b. write-back cache


I understand that bus watching means that each cache snoops the bus to see what requests are sent form other caches to the main memory, but I don't really understand which answer is correct.

First type (write-through) would just update everything to the memory every time something is updated and the latter would just keep data in cache to be faster and to me it seems that both could work.

Any help is appreciated.

• The question is ambiguous. Both types are used in multiprocessor architectures, they can be combined (for example write-thru L1, write-back L2, shared multi-cpu write-back L3...). If bus watching is for debugging, a write-thru cache is obviously more adequate. – TEMLIB Apr 23 '17 at 20:15