What is the purpose of RAM in a computer?

RAM (Random Access Memory) is a form of memory which is used to save data about programs that are currently open. RAM is much faster than a HDD or SSD, and so the CPU has to spend less time in the "fetch" part of the "fetch-decode-execute" - that means more time doing calculations!Unfortunately, RAM is volatile (meaning that it loses its data when we turn off the power), and it is more expensive per GB than a HDD or SSD. This limits our usage of RAM, and the amount that we're able to install into our systems.