Random access memory, or RAM, is temporary, short-term memory that a computer uses to store the essential parts of the operating system and the program code and data that the computer is currently running. The contents of RAM are lost when the computer is switched off or the data contained in RAM is no longer needed, such as when the program using the data is closed. RAM is therefore known as volatile memory.
Physically, RAM consists of electrical circuits etched on tiny wafers of a semiconductor--a substance with electrical conductivity intermediate between that of a conductor and an insulator, such as silicon. Each of these so-called memory chips consists of millions of transistors and capacitors, which combine to store a binary digit, or “bit”--a “1” or a “0”--in a memory cell. The memory chips are arranged onto small printed circuit boards, known as memory modules, that plug into the motherboard of the computer.
Random access refers to the fact that the central processing unit (CPU) of the computer can access each memory cell in RAM directly, or randomly, without needing to access previous cells. This makes the process of writing and reading data to and from RAM must faster than if the CPU had to search sequentially through all the data stored in RAM. Indeed, accessing RAM is much faster than accessing the hard disk or removable media, such as CD or DVD.
If you open several large programs simultaneously, you may approach the limit of the physical RAM installed on your computer, but you cannot completely run out. The operating system reserves a portion of the hard disk, known as virtual memory, which it uses as an extension of physical RAM. If physical RAM becomes scarce, the computer exchanges, or swaps, parts of the programs and data between memory and hard disk storage; this slows down its operation but allows it to keep working.
RAM capacity is measured in bytes (8 bits = 1 bytes), megabytes (1 megabyte = 1,048,576 bytes) or gigabytes (1 gigabyte = 1,073,741,824 bytes). Regular 32-bit processors can theoretically use up to 4 GB of RAM, while 64-bit processors, in combination with 64-bit operating systems, can use up to 128 GB or more. The important point is that a computer should have enough RAM to load the operating systems and run all the programs that you commonly use. Operating systems and programs typically specify a minimum requirement for RAM, but if you plan to run several large programs simultaneously, it's a good idea to install more than the minimum requirement.