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), and then the 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. What is the average time in ns required to access a referenced word on this system?
Answer to relevant QuestionsSuppose a stack is to be used by the processor to manage procedure calls and returns. Can the program counter be eliminated by using the top of the stack as a program counter? Suppose the hypothetical processor of Figure 1.3 also has two I/O instructions: 0011 = Load AC from I/O 0111 = Store AC to I/O In these cases, the 12-bit address identifies a particular external device. Show the program ...List and briefly explain five storage management responsibilities of a typical OS. For the processing model of Figure, briefly define each state. Assume that at time 5 no system resources are being used except for the processor and memory. Now consider the following events: At time 5: P1 executes a command to read from disk unit 3. At time 15: P5’s time slice ...
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