RAM
also: Random Access Memory, main memory, physical memory
RAM (Random Access Memory) is the computer's fast, temporary memory used to store data and programs currently in use. It's erased when the system powers off.
RAM is volatile memory that the CPU uses to store and quickly access data while running programs and the operating system. Unlike disk storage (SSD/HDD), RAM is much faster but loses all its contents when power is cut.
In Linux, you can check available RAM using the free command, which shows total memory, used memory, and available memory in kilobytes or human-readable format. For example, free -h displays output like: total 15Gi, used 8Gi, available 7Gi.
The kernel manages RAM through virtual memory and paging, allowing the system to use disk space as overflow when RAM fills up—though this is much slower. Linux also caches frequently-accessed disk data in RAM to speed up file operations, which is why the "available" memory may differ from "free" memory.