A system has two levels of cache L1 and L2 between processor and main memory. If a referenced word is in L1, 10 ns are required to access it. The look-up time for L2 is 20 ns. L1 hit ratio is 30% and L2 hit ratio is 50%.
When neither of the caches contains the word, main memory is checked. It takes 0.1 microseconds to look up an item in main memory, but the success rate is 80%.
The word can always be found on the disk and takes 1 millisecond to access it from disk. Calculate the effective access time for a referenced word.