Linux memory: buffer vs cache

"Buffers" represent how much portion of RAM is dedicated to cache disk block. 

"Cached" is similar like "Buffers", only this time it caches pages from file reading.

Buffers
are associated with a specific block device, and cover caching of filesystem metadata as well as tracking in-flight pages. 

The
cache only contains parked file data. 

That
is, the buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. 

The
cache only contains the contents of the files themselves.

Short answer: 

Cached is the size of the page cache. 

Buffers is the size of in-memory block I/O buffers. 

Cached matters; Buffers is largely irrelevant.

Long answer: 

Cached is the size of the Linux page cache, minus the memory in the swap cache, which is represented by SwapCached (thus the total page cache size is Cached + SwapCached). 

Linux performs all file I/O through the page cache. Writes are implemented as simply marking as dirty the corresponding pages in the page cache; the flusher threads then periodically write back to disk any dirty pages. Reads are implemented by returning the
data from the page cache; if the data is not yet in the cache, it is first populated. On a modern Linux system, Cached can easily be several gigabytes. It will shrink only in response to memory pressure. The system will purge the page cache along with swapping
data out to disk to make available more memory as needed.

Buffers are in-memory block I/O buffers. They are relatively short-lived. Prior to Linux kernel version 2.4, Linux had separate page and buffer caches. Since 2.4, the page and buffer cache are unified and Buffers is raw disk blocks not represented in the page
cache—i.e., not file data. The Buffers metric is thus of minimal importance. On most systems, Buffers is often only tens of megabytes.