Operating System

Operating System

Assignment #1 .

30 Points

0. Suppose the hypothetical processor of Figure 1.3 also has two I/O instructions:

0111 = Load AC from I/O

1000 = Store AC to I/O

1.13. A computer has a cache, main memory, and a disk used for virtual memory. 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, 60 ns are needed to load it into the cache (this includes the time to originally check the cache), then the reference is started again. If the word is not in main memory, 12 ns are required to fetch the word from disk, followed by 60 ns to copy it to the cache, then the reference is started again. The cache hit ratio is 0.9 and the main memory hit ratio is 0.6. What is the average time in ns required to access a referenced word on this system?.

Given:

Cache access time = 20ns

Cache hit rate = 0.9

Cache miss rate = 1 – 0.9 = 0.1

RAM access time = 60 ns

RAM hit rate = 0.6

RAM miss rate = 1 – 0.6= 0.4

Disk access time = 12 ns