Why is Redis called an in-memory database?

Redis is called an in-memory database, because all data is stored and processed in RAM, rather than on a hard drive or SSD like traditional databases.

#What this means technically

• When an application writes or reads data from Redis, it's reaching into RAM, not the filesystem.
• That makes operations thousands of times faster, since accessing RAM takes nanoseconds, while accessing disk takes milliseconds.

#How Redis persists data

Although Redis is in-memory, it can save a copy of the data to disk, so nothing is lost on restart:

• RDB (snapshotting), periodic memory snapshots.
• AOF (Append Only File), logging every operation. On startup, Redis can restore data from these files back into memory.

#Why this matters

• Speed: ideal for caches, sessions, queues.
• Low latency: every operation runs instantly.
• Flexibility: you can choose whether to persist data to disk, or keep everything only in memory (volatile).

Summary: Redis is in-memory because its primary storage is RAM, and disk is used only for backup persistence. That's what gives Redis its maximum data-access speed.