Regenerative capacitor memory is a type of computer memory that uses the electrical property of capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

 to store the bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s of data. Because the stored charge slowly leaks away, these memories must be periodically regenerated (i.e. read and rewritten, also called refresh

Memory refresh

Memory refresh is the process of periodically reading information from an area of computer memory, and immediately rewriting the read information to the same area with no modifications. Each memory refresh cycle refreshes a succeeding area of memory. Memory refresh is most often associated with...

ed) to prevent data loss.

Other types of computer memory exist that use the electrical property of capacitance to store the data, but do not require regeneration. However these have either been somewhat impractical (e.g., the Selectron tube

Selectron tube

The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America under the direction of Vladimir Zworykin, of television technology fame...

) or are usually considered to be read-only memory

Read-only memory

Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

 (e.g., EPROM

EPROM

An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

, Flash memory

Flash memory

Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

) because writing takes significantly longer than reading them.

History

The first regenerative capacitor memory built was the rotating capacitor drum memory of the Atanasoff–Berry Computer (1942). Each of its two drums stored thirty 50-bit binary numbers, rotated at 60 rpm and was regenerated every rotation (1 Hz refresh rate).

The first random access

Random access

In computer science, random access is the ability to access an element at an arbitrary position in a sequence in equal time, independent of sequence size. The position is arbitrary in the sense that it is unpredictable, thus the use of the term "random" in "random access"...

 regenerative capacitor memory was the Williams tube

Williams tube

The Williams tube or the Williams-Kilburn tube , developed in about 1946 or 1947, was a cathode ray tube used to electronically store binary data....

 (1947). Typically they stored 512 to 1K bits, the refresh rate required varied depending on the type of CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

 used.

The modern DRAM

Dynamic random access memory

Dynamic random-access memory is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1...

(1966) is a regenerative capacitor memory.