Final answer:
Direct mapping in the cache assigns each memory address to a specific cache entry. The cache size affects system performance, with a larger cache size leading to faster access times. Physically addressed cache stores data based on physical addresses, while a 4-byte line can result in inefficient cache utilization.
Step-by-step explanation:
a) Significance of direct mapping in the cache:
Direct mapping is a cache mapping technique in which each block of memory can only be mapped to a specific location in the cache. This means that each location in the cache is assigned a fixed set of memory addresses. In this case, with a direct-mapped cache, each memory address is mapped to a specific cache entry. This allows for fast indexing and retrieval of data from the cache, but it can also lead to cache conflicts and reduced cache utilization.
b) Impact of cache size on system performance:
The cache size affects the overall system performance. A larger cache size allows for a greater amount of data to be stored in the cache, reducing the need to access data from slower main memory. This leads to faster access times and higher cache hit rates. On the other hand, if the cache size is too small, it may result in a higher cache miss rate and more frequent accesses to main memory, which can slow down the system.
c) Role of physically addressed cache:
A physically addressed cache stores data based on the physical addresses of memory locations. This allows for efficient retrieval of data, as the physical address can be used directly to access the corresponding cache entry. This differs from a virtually addressed cache, which uses virtual addresses that need to be translated to physical addresses before accessing the cache.
d) Impact of a 4-byte line on cache efficiency:
A 4-byte line refers to the unit of data that is fetched from memory into the cache. With a 4-byte line size, each cache entry can hold 4 bytes of data. This means that if a request is made for a single byte of data, the entire 4-byte line containing the requested byte will still be loaded into the cache. This can lead to inefficiencies in cache utilization, as additional space in the cache is occupied by unused data.