Principal of Locality of Reference:
The principal of locality of reference is a fundamental concept in computer science and computer architecture. It states that a program tends to access a relatively small portion of its address space at any given time. This principle is based on the observation that programs often exhibit temporal and spatial locality.

Cache Memory:
Cache memory is a small, fast memory that is located closer to the CPU than main memory. It serves as a buffer between the CPU and main memory, allowing the CPU to access frequently used data and instructions quickly. Cache memory is based on the principle of locality of reference.

Justification of Cache Memory:
Cache memory is justified by the principal of locality of reference for several reasons:

1. Temporal Locality:
Temporal locality refers to the tendency of a program to access the same data or instructions repeatedly over a short period of time. Cache memory takes advantage of temporal locality by storing recently accessed data and instructions. When the CPU requests a particular data or instruction, the cache memory is checked first. If the data or instruction is found in the cache (cache hit), it can be accessed much faster than if it had to be retrieved from main memory (cache miss).

2. Spatial Locality:
Spatial locality refers to the tendency of a program to access data or instructions that are located close to each other in memory. Cache memory takes advantage of spatial locality by storing data and instructions that are located near each other in main memory. When the CPU accesses a particular memory location, cache memory also retrieves nearby data and instructions and stores them in the cache. This reduces the average memory access time because the CPU is likely to access these nearby data or instructions in the near future.

3. Cache Hierarchy:
Modern computer systems often employ multiple levels of cache memory, known as a cache hierarchy. Each level of cache is larger but slower than the previous level. The cache hierarchy is designed to further exploit the principle of locality of reference. The higher levels of cache (e.g., L2 cache) store data and instructions that are accessed less frequently, while the lower levels of cache (e.g., L1 cache) store frequently accessed data and instructions. This hierarchical organization allows for faster access to frequently used data and instructions, while still providing larger storage capacity for less frequently used data.

Conclusion:
The principal of locality of reference justifies the use of cache memory in computer systems. Cache memory takes advantage of the temporal and spatial locality exhibited by programs, resulting in faster access to frequently used data and instructions. By storing recently accessed data and instructions close to the CPU, cache memory reduces the average memory access time and improves overall system performance.