What are the differences between the Free sections?

Differences between sections in the output of the free command relate to the types of memory shown and their usage status.

Main sections:

• total: Total available physical RAM.
• used: Amount of memory currently used by processes.
• free: Amount of memory that is not used at all and available for immediate allocation.
• shared: Memory shared by multiple processes (e.g., shared memory segments).
• buff/cache: Memory used by the kernel for disk I/O buffers and page cache. This data can be quickly freed if programs need other memory.
• available: A more accurate estimate of actually available memory for new processes, calculated considering buff/cache, free, and other reclaimable memory.

In older versions of free, instead of buff/cache, there might have been separate columns buffers and cached. In newer versions, they are combined. There may also be a Swap line for swap partition information.