Memcached is a simple distributed in-memory cache for high-throughput key-value lookups. It is most useful when cached data can be regenerated from a durable source and the application only needs get, set, expiration, and simple counters.

Redis has a richer feature set, but Memcached is still a good choice for pure caching. In interviews, the important points are when Memcached is enough, how client-side sharding works, and what happens when a cache node fails.

For interviews, focus on architecture, consistent hashing, memory management, scaling behavior, cache failure modes, and where Redis is the better choice.

The diagram maps out how application servers, the client library, and the Memcached cluster relate to each other, with the consistent hash ring sitting between the application tier and the individual cache nodes.