What is the cache?

• A. This is fast access memory (faster than RAM), it stores frequently used data for fast access.
• B. A type of slow storage device
• C. A register in the CPU
• D. An external keyboard device

Answer: (A)

Cache is small, fast memory placed close to the processor to hold copies of data and instructions the CPU is likely to reuse soon. Because caches can be accessed much quicker than main memory, keeping frequently used data there dramatically reduces the time the CPU spends waiting for data. When the CPU needs something, it first checks the cache; if the data is there (a cache hit), it can use it immediately. If not (a cache miss), the data is fetched from RAM and stored in the cache for future use. Caches are organized in levels (L1, L2, L3) with different speeds and sizes, working on the principle of temporal and spatial locality—the idea that recently used data and nearby data will be used again soon. The option that describes fast access memory that stores frequently used data best captures what a cache is. The other choices describe slow storage, a register, or an external keyboard, which do not fit.