Suppose cache with hit ratio 'Ch' and access time 'Ct' is given and main memory with hit ratio 'Mh' and access time 'Mt' is given and a disk with access time 'Dt' is given. If with only this information average memory access time is asked, does the access time of main memory include time of cache and memory also.
For e.g. should the equation be -
Average memory access time = Ch * Ct + (1-Ch) * Mh * ( Ct + Mt ) + (1-Ch) * (1-Mh) * ( Ct + Mt + Dt)
If so, why the addition and is it implicit always ?