What is RAM and what does it do?

What is RAM and what does it do?
RAM - Random Access Memory, or volatile memory, is used by the system to store data for processing by a computer's central processing unit (CPU), also known as the processor. RAM stores the data in memory cells that are arranged in grids much like the cells are arranged in a spreadsheet, from which data, in the binary form of 1's and 0's, can be accessed and transferred at random to the processor for processing by the system's software.
The data stored in a hard disk drive (HDD) cannot be accessed at random. Whole sectors, containing blocks of data, are transferred from a hard disk drive, placed in a large swap file on the same drive, and only then are selected files transferred to RAM for random access by the processor, which is itself only performing the instructions of the system's operating system (usually Windows), and its application software.  
Whenthe computer is turned off, all of the data in the RAM memory is lost, hence its alternative name of volatile memory, whereas all of the data on a hard disk drive is retained permanently until it is intentionally erased. The motherboard (or mainboard) manual (that should be provided with a new or a second-hand PC) will provide all of the details about the different types of supported RAM, and the various combinations of modules per bank for each type that can be successfully installed.
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