Cache memory in computer organization is a high-speed, small-sized type of volatile computer memory that stores frequently used computer programs, applications, and data. Here's an overview in seven points:
Purpose of Cache Memory: Cache memory serves as a buffer between the CPU (central processing unit) and the main memory (RAM). Its primary purpose is to reduce the average time to access data from the main memory by storing frequently used data closer to the CPU.
Levels of Cache: Modern computers have multiple levels of cache, typically L1, L2, and sometimes L3. L1 is the closest to the CPU and is the smallest but fastest. L2 is larger but slightly slower, and L3, if present, is larger but slower than L2.
Cache Hit and Cache Miss: A cache hit occurs when the CPU finds the required data in the cache memory, resulting in a faster data access. A cache miss occurs when the data is not in the cache, leading to a slower access as the CPU fetches it from the main memory.
Cache Replacement Policies: Cache memory employs replacement policies like Least Recently Used (LRU) or First-In, First-Out (FIFO) to decide which data to remove when new data needs to be stored due to limited cache size.
Write Policies: Cache can use write-back or write-through policies. Write-back writes data to the cache first and then to the main memory, improving write performance. Write-through writes data simultaneously to the cache and main memory for data integrity.
Cache Coherence: In multi-core or multi-processor systems, cache coherence protocols ensure that all processors see a consistent view of memory. Common protocols include MESI (Modified, Exclusive, Shared, Invalid) and MOESI (Modified, Owned, Exclusive, Shared, Invalid).
Cache Size and Trade-offs: Cache size is a trade-off between cost, speed, and efficiency. Larger caches can store more data but may be slower, and too much cache can lead to longer access times due to increased complexity.