You need to find the time to access a reference word.
Question: A computer has a cache, main memory, and a disk. If a referenced word is in the cache, 20 ns are required to access it.
- If it is in main memory but not in the cache (called cache miss), 60 ns are needed to load it into the cache (this includes the time to originally check the cache), and then reference is started again.
- If the word is not in main memory, 12 ms are required to fetch the word from disk, followed by 60 ns to copy it to the cache, and then the reference is started again. The cache hit ratio is 0.9 and the main memory hit ratio is 0.6.
Question: What is the average time in nanoseconds required to access a referenced word on this system?
Provide answer in detail: no word count.