Dynamic RAM is the standard computer memory of the vast majority of modern desktop computers. It is a volatile memory that needs to be refreshed with voltage regularly, otherwise it loses the information stored on it. Dynamic RAM is also referred to as DRAM. Volatile means that it loses the information stored on it as soon as power is withdrawn.
A random access memory (RAM) chip is a series of transistors and capacitors on a piece of silicon connected by circuitry. The capacitor is the element that stores the information and needs to be constantly charged with voltage, and refreshed to keep it. The voltage fades away quite quickly, and because these capacitors are small, they need to be refreshed often. This is where the "dynamic" element comes into play; each dynamic RAM chip has logic built into it which automatically refreshes each capacitor many times a second.
If the particular capacitor has data stored in it, it is powered regularly by the refresh. If it is empty, it is left unpowered. Each refresh is the logic reading each capacitor, checking to see if it has information, powering it if it does, and leaving it unpowered if it does not. This process happens many times a second and is one of the determining factors of how fast dynamic RAM is.
Dynamic RAM is referred to by its size and speed. For example, the packaging or description of the memory module might list 1066 Mhz 1 Gb DRAM. The 1066 Mhz is the speed at which a computer can read and write to the memory, and the higher number the better. The 1 Gb is the usable space on the chip; in this example, the chip can store 1 gigabyte of information on it while it has power. There are several different types of DRAM.
One type of DRAM is Double In-line Memory Module (DIMM), and it is the most popular type of memory for server and home use. Each side of the chip has connections, or pins, at the bottom and each side is separate, carrying more connections to the motherboard. Another type, Small Outline Double In-line Memory Module (SO-DIMM), is a smaller version of DIMM. SO-DIMM is used in laptops, routers, printers, and other smaller devices that use memory. The two types of memory work in exactly the same way as dynamic RAM, but are smaller and therefore more expensive to produce and buy.