Solution

The correct answer is 200 ns

Explanation:

• Hit ratio: 0.9 (This means 90% of the time, the data is found in the cache)
• Cache access time: 100 ns
• Miss ratio: 1 - 0.9 = 0.1 (This means 10% of the time, the data is not found in the cache and needs to be retrieved from main memory)
• Main memory access time: 1100 ns

The average access time is a weighted average of the access times for cache hits and cache misses. We can calculate it using the following formula:

• Average access time = (Hit ratio × Cache access time) + (Miss ratio × Main memory access time)

Plugging in the values:

• Average access time = (0.9 × 100 ns) + (0.1 × 1100 ns)
• Average access time = 90 ns + 110 ns
• Average access time = 200 ns

Therefore, the average access time for this system is 200 ns. This value is significantly lower than the main memory access time because the cache hits are much faster and happen more frequently (90% of the time).