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A computer has a cache and main memory 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. The cache hit ratio is 0.9. What is the average time in ns required to access a referenced word on this system?
Correct answer is '26'. Can you explain this answer?
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A computer has a cache and main memory used for virtual memory. If a r...
Cache and Main Memory:
- A computer system typically has multiple levels of memory hierarchy, including cache and main memory.
- Cache is a small, fast memory that stores a subset of the data and instructions that are most frequently accessed by the CPU.
- Main memory is a larger, slower memory that stores the rest of the data and instructions.
Access Time:
- The access time is the time required to fetch a word from a specific memory level.
- In this system, if a referenced word is in the cache, it takes 20 ns to access it.
- If the word is not in the cache but is in main memory, it takes 60 ns to load it into the cache.
Cache Hit Ratio:
- The cache hit ratio is the percentage of memory references that result in a cache hit.
- In this system, the cache hit ratio is 0.9, which means that 90% of the memory references result in a cache hit.
Average Access Time:
To calculate the average time required to access a referenced word, we need to consider both cache hits and cache misses.
Cache Hits:
- When there is a cache hit, it takes 20 ns to access the word.
- Since the cache hit ratio is 0.9, the average time for cache hits is 0.9 * 20 ns = 18 ns.
Cache Misses:
- When there is a cache miss, it takes 60 ns to load the word into the cache.
- Since the cache hit ratio is 0.9, the cache miss ratio is 1 - 0.9 = 0.1.
- The average time for cache misses is 0.1 * 60 ns = 6 ns.
Overall Average Time:
To calculate the overall average time, we need to consider the weighted average of cache hits and cache misses.
- The weighted average time for cache hits is 0.9 * 18 ns = 16.2 ns.
- The weighted average time for cache misses is 0.1 * 6 ns = 0.6 ns.
- The overall average time is the sum of the weighted average times for cache hits and cache misses: 16.2 ns + 0.6 ns = 16.8 ns.
Answer:
The average time required to access a referenced word on this system is 16.8 ns.
- A computer system typically has multiple levels of memory hierarchy, including cache and main memory.
- Cache is a small, fast memory that stores a subset of the data and instructions that are most frequently accessed by the CPU.
- Main memory is a larger, slower memory that stores the rest of the data and instructions.
Access Time:
- The access time is the time required to fetch a word from a specific memory level.
- In this system, if a referenced word is in the cache, it takes 20 ns to access it.
- If the word is not in the cache but is in main memory, it takes 60 ns to load it into the cache.
Cache Hit Ratio:
- The cache hit ratio is the percentage of memory references that result in a cache hit.
- In this system, the cache hit ratio is 0.9, which means that 90% of the memory references result in a cache hit.
Average Access Time:
To calculate the average time required to access a referenced word, we need to consider both cache hits and cache misses.
Cache Hits:
- When there is a cache hit, it takes 20 ns to access the word.
- Since the cache hit ratio is 0.9, the average time for cache hits is 0.9 * 20 ns = 18 ns.
Cache Misses:
- When there is a cache miss, it takes 60 ns to load the word into the cache.
- Since the cache hit ratio is 0.9, the cache miss ratio is 1 - 0.9 = 0.1.
- The average time for cache misses is 0.1 * 60 ns = 6 ns.
Overall Average Time:
To calculate the overall average time, we need to consider the weighted average of cache hits and cache misses.
- The weighted average time for cache hits is 0.9 * 18 ns = 16.2 ns.
- The weighted average time for cache misses is 0.1 * 6 ns = 0.6 ns.
- The overall average time is the sum of the weighted average times for cache hits and cache misses: 16.2 ns + 0.6 ns = 16.8 ns.
Answer:
The average time required to access a referenced word on this system is 16.8 ns.
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A computer has a cache and main memory used for virtual memory. If a r...
As cache hit ratio is 0.9 and cache miss is 0.1, the time required if referenced word is in cache is 20 ns, while time required to access word which is not in cache is 20 + 60 = 80 ns.
0.9 × 20 + 0.1(60 + 20) = 26 ns
0.9 × 20 + 0.1(60 + 20) = 26 ns
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A computer has a cache and main memory 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. The cache hit ratio is 0.9. What is the average time in ns required to access a referenced word on this system?Correct answer is '26'. Can you explain this answer?
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A computer has a cache and main memory 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. The cache hit ratio is 0.9. What is the average time in ns required to access a referenced word on this system?Correct answer is '26'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about A computer has a cache and main memory 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. The cache hit ratio is 0.9. What is the average time in ns required to access a referenced word on this system?Correct answer is '26'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A computer has a cache and main memory 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. The cache hit ratio is 0.9. What is the average time in ns required to access a referenced word on this system?Correct answer is '26'. Can you explain this answer?.
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