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Word Origin and Invention Origin

Volatile memory is memory that loses its data when unplugged. Computer RAM is one common example of volatile memory.

• RAM (Random Access Memory).
• NVRAM (Non Volatile RAM) NOTE: I know this seems misplaced here, but it will be explained below.
• DRAM (Dynamic RAM)
• SDRAM (Synchronous DRAM)
• SRAM (Static RAM)

Simple Explanation

Volatile substances are those that tend to disintegrate and float away easily; in the same way, volatile memory tends to disappear easily and unless held in place will “float away.”

By “float away” we don't mean that the memory chips themselves will float away, but instead we mean that the data stored on the chips will tend to disintegrate and fade into non-existence unless we do something to hold it in place.

So what do we do to hold volatile memory in place? We keep the chips attached to a power source. As long as a volatile memory chip has power it will retain its data, but as soon as that power is disconnected the data will fade, and often within a matter of seconds that data will disappear.

Kinds and their Uses

RAM: Random Access Memory allows access to any portion of memory without dependence on the what was accessed previously or what is to be accessed next -- many memory devices are unable to operate in this manner (eg: DVDs, hard drives, CDROMs, etc). Many ROM (Read Only Memory) chips are also, in this technical sense, RAM; however, in the electronics industry the RAM acronym has come to refer almost exclusively to volatile memory.

Kinds:

• NVRAM
• SRAM
• DRAM
• SDRAM
• many many more.

Programming:

• These chips very easily receive data. Writing is very fast, and bytes do not have be erased to be over-written.

Erasure::

• Not required

Part Number Prefixes (partial list):

• 52
• 62

NVRAM: Non Volatile RAM, as the name implies, is functionally not a volatile memory; however, NVRAM uses volatile RAM technologies and simply adds a battery, etcetera, to make the data persist when power is removed.

Components:

• Battery: A built-in battery protects the data when the power is removed. Some of these claim to have batteries with life spans of 10-years.
• EEPROM: These have an additional EEPROM that corresponds to the RAM memory space. When power is removed, these devices transfer all the data from RAM to the EEPROM. When power is restored, then all the data is copied back into the RAM from the EEPROM.

Programming and Erasure:

• All the qualities of RAM are retained

Part Number Prefixes (partial list):

• 45Z
• DS12
• XS22

DRAM: Dynamic RAM stores its data in small, individual capacitors. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, this is a dynamic memory as opposed to SRAM and other static memory.

Advantages:

• Simplicity; only one capacitor and transistor per memory cel
• Density; smaller memory cells mean that we can fit more cells in the same area.

Disadvantages:

• Power hungry; requires regular refreshes
• Generates heat; higher power usage also often means more heat generation

SDRAM: Synchronous DRAM is the same as regular DRAM, except that SDRAM uses special signals, called “clock pulses,” to time and synchronize data retrieval and writing operations, this allows SDRAM to use its bandwidth more efficiently (ie: SDRAM is faster than DRAM).

Kinds:

• non DDR: This typically has no special designation.
• DDR, DDR2, DDR3, DDR4: DDR stands for Double Data Rate, and this kind of SDRAM and its revisions runs at upwards of twice the speed that plain SDRAM is capable of at the same clock speed.

Advantages:

• Faster than asynchronous DRAM (“DRAM” for short)
• High amount of memory in a small package>

Disadvantages:

• Volatile; can't maintain its data when power is cut off

Uses:

• Commonly used in personal computers as general-purpose runtime memory

SDRAM: Static RAM uses a memory cell made with (a minimum of) six transistors in a flip-flop configuration. The SRAM memory cell does not require refreshes and so is static rather than dynamic; however, the cell will lose its state when power is removed, making it a volatile memory.

Kinds:

• Synchronous: Data operations are all timed by clock pulses.
• Asynchronous: Data operations are independent of any clock pulse.
• Bipolar junction transistor: Very fast, but consumes a lot of power.
• MOSFET: Low power and very common.

Advantages:

• Significantly less power consuming than DRAM, unless being accessed highly frequently
• Faster than DRAM
• Simpler interface

Disadvantages:

• Holds less memory than DRAM in the same size package
• Higher priced than DRAM

Uses:

• Hobbyists often prefer SRAM due to the ease of interfacing. It is much easier to work with than DRAM as there are no refresh cycles and the address and data buses are directly accessible rather than multiplexed. In addition to buses and power connections, SRAM usually requires only three controls: Chip Enable (CE), Write Enable (WE) and Output Enable (OE).
• Caches in CPUs, PLDs, Microprocessors, etcetera
• Buffers of all kinds; used in hard disks, cdrom drives, routers, etcetera
• Some amount is embedded in practically all modern appliances and electronic toys … anything that implements an electronic user interface.