What’s the Real Difference Between Linux Buffers and Cache?

Buffer and Cache Definitions

Buffer : temporary storage for raw disk blocks before writing to disk, usually small (around 20 MB); the kernel aggregates writes for optimization.

Cache : page cache for data read from files, allowing fast memory retrieval on subsequent accesses.

Although Buffer primarily caches data to be written, it can also cache data read from disk; similarly, Cache can be used for writes.

free Command

The free command shows memory usage, including Buffers and Cache as part of buff/cache. Its data comes from /proc/meminfo, which is part of the /proc virtual filesystem.

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        1.0G        394M        2.6M        491M        728M
Swap:            0B          0B          0B

In man proc, Buffers are temporary storage for raw disk blocks, and Cached is the in‑memory page cache.

Experiments

Write Cache

Clear caches via /proc/sys/vm/drop_caches (write 3). Run vmstat 2 in terminal 1 and perform writes in terminal 2. Observe that cache grows while buffer stays roughly constant.

Read Buffer

After clearing caches again, run vmstat 2 and read data with dd in terminal 2. Both buffer and cache increase, but Buffer grows faster, showing that disk reads are cached in Buffer.

Reading files caches data in Cache ; reading from disk caches data in Buffer .

Conclusion

Buffer can cache data both for writing to disk and for reading from disk.

Cache can serve as page cache for both reading files and writing files.