The primary function of a cache in computing is to store frequently accessed data temporarily. By keeping copies of data closer to the CPU, the cache reduces latency and enhances performance. This allows for quicker data retrieval compared to fetching from the main memory. Different levels of cache, such as L1, L2, and L3, exist, with varying sizes and speeds. The cache operates on the principle of locality of reference, which assumes that recently accessed data will likely be accessed again soon. Thus, an efficient cache system is crucial for achieving optimal computing performance.