Memory cell (binary)

The memory cell is the fundamental building block of computer memory . The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 (high voltage level) and reset to store a logic 0 (low voltage level). Its value is maintained / stored until it is changed by the set / reset process. The value in the memory can be accessed by reading it.

Over the history of computing Many different memory cell architectures-have-been used Including core memory and bubble memory , purpose The Most common ones used are flip-flops and capacitors.

The SRAM, static ram memory cell is a type of flip-flop circuit, usually implemented using FETs . These require very low power when not being accessed.

A second type, DRAM is based around a capacitor. Charging and discharging this capacitor can a ‘1’ or a ‘0’ in the cell. However, this capacitor will slowly leak away, and must be refreshed periodically. Because of this refresh process, DRAM uses more power, but can achieve greater storage densities.

History

On December 11, 1946 Freddie Williams applied to a cathode-ray tube (CRT) storing device ( Williams tube ) with 128 40- bit words. It was operational in 1947 and is considered the first practical implementation of random-access memory . [1] In this year, the first applications for magnetic-core memory were filed by Frederick Viehe. An Wang , Ken Olsen and Jay Forrester also contributed to its development. The first modern memory cells were introduced in 1969, when John Schmidt designed the first 64-bit MOS p-channel SRAM . The first bipolar 64-bit SRAM was released by Intel in 1969 with the 3101 Schottky TTL . One year later it released the first DRAM chip, the Intel 1103 . [2]

Description

The memory cell is the fundamental building block of memory. It can be implemented using different technologies, such as bipolar , MOS , and other semiconductor devices . It can also be manufactured from magnetic material such as ferrite cores or magnetic bubbles. [3] The purpose of the binary memory cell is always the same. It stores one bit of binary information and it must be set to store a 1 and reset to store a 0. [4]

Implementation

The following schematics detail the three most used implementations for memory cells:

  • The Dynamic Random Access Memory Cell (DRAM)
  • The Static Random Access Memory Cell (SRAM)
  • Flip flops like the J / K shown below.

Applications

Logic circuits without memory cells or feedback paths are called combinational , their outputs depend on the current value of their input values. They do not have memory. But memory is a key element of digital systems . In computers, it allows to store both programs and data and memory cells. Logic circuits that use memory cells are called sequential circuits. Its output depends not only on the present value of its inputs, but also on the circuits. These circuits require a timing generator or clock for their operation. [5]

Computer memory used in computer systems is built mainly out of DRAM cells, since the layout is much smaller than SRAM, it can be more densely packed yielding cheaper memory with greater capacity. Since the DRAM memory cell stores its value as a charge of a capacitor, it has to be constantly rewriten. DRAM cells slower than the SRAM (Static RAM) cells, which has its value always available. This is the reason why SRAM is used for on- chip cache in microprocessor chips. [6]

See also

  • Dynamic random-access memory
  • Flip-flop (electronics)
  • Row hammer
  • Static random-access memory

References

  1. Jump up^ O’Regan, Gerard (2013). Giants of Computing: A Compendium of Select, Pivotal Pioneers . Springer Science & Business Media. p. 267. ISBN  1447153405 . Retrieved 13 December 2015 .
  2. Jump up^ W. Pugh, Emerson; R. Johnson, Lyle; H. Palmer, John (1991). IBM’s 360 and Early 370 Systems . MIT Press . p. 706. ISBN  0262161230 . Retrieved 9 December 2015 .
  3. Jump up^ D. Tang, Denny; Lee, Yuan-Jen (2010). Magnetic Memory: Fundamentals and Technology . Cambridge University Press . p. 91. ISBN  1139484494 . Retrieved 13 December 2015 .
  4. Jump up^ Fletcher, William (1980). An engineering approach to digital design . Prentice-Hall. p. 283. ISBN  0-13-277699-5 .
  5. Jump up^ Microelectronic Circuits (Second ed.). Holt, Rinehart and Winston, Inc. 1987. p. 883. ISBN  0-03-007328-6 .
  6. Jump up^ “The Technical Question: the cache, how does it work?” . PC World Fr .

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