Semiconductor memory
Encyclopedia
Semiconductor memory is an electronic data storage device
, often used as computer memory
, implemented on a semiconductor
-based integrated circuit
. Examples of semiconductor memory include non-volatile memory
such as Read-only memory
(ROM), magnetoresistive random access memory (MRAM), and flash memory
. It also includes volatile memory
such as static random access memory
(SRAM), which relies on several transistors forming a digital flip-flop
to store each bit
, and dynamic random access memory
(DRAM), which uses one capacitor
and one transistor to store each bit. Shift register
s, processor register
s, data buffers and other small digital registers that have no memory address decoding mechanism
are not considered as memory.
Data is accessed by means of a binary memory address
to the memory. If the memory address consists of M bits, the address area consists of 2^M addresses per chip. Semiconductor memory are manufactured with a certain word length (number of 1-bit cells sharing the same memory address) that power of two, typically M=1, 2, 4 or 8 bit per chip. Consequently, the amount of data stored in each chip is
bits. Possible figures are 1, 2, 4, 8, 16, 32, 64, 128, 256 and 512 bit
, kbit, Mbit, Gbit and Tbit, here defined by binary prefix
es. By combining several integrated circuits, memory can be arranged for a larger word length and/or address space than what is offered by each chip, often but not necessarily a power of two
.
Data storage device
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, often used as computer memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
, implemented on a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
-based integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
. Examples of semiconductor memory include non-volatile memory
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
such as 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...
(ROM), magnetoresistive random access memory (MRAM), and 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...
. It also includes volatile memory
Volatile memory
Volatile memory, also known as volatile storage, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply...
such as static random access memory
Static random access memory
Static random-access memory is a type of semiconductor memory where the word static indicates that, unlike dynamic RAM , it does not need to be periodically refreshed, as SRAM uses bistable latching circuitry to store each bit...
(SRAM), which relies on several transistors forming a digital flip-flop
Flip-flop
Flip-flops, thongs, Japanese sandals, or jandals are an open type of outdoor footwear, consisting of a flat sole held loosely on the foot by a Y-shaped strap, like a thin thong, that passes between the first and second toes and around either side of the foot...
to store each 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...
, and dynamic random access memory
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...
(DRAM), which uses one capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
and one transistor to store each bit. Shift register
Shift register
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...
s, processor register
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
s, data buffers and other small digital registers that have no memory address decoding mechanism
Address decoder
In digital electronics, an address decoder is a decoder circuit that has two or more bits of an address bus as inputs and that has one or more device selection lines as outputs. When the address for a particular device appears on the address bus, the address decoder asserts the selection line for...
are not considered as memory.
Data is accessed by means of a binary memory address
Memory address
A digital computer's memory, more specifically main memory, consists of many memory locations, each having a memory address, a number, analogous to a street address, at which computer programs store and retrieve, machine code or data. Most application programs do not directly read and write to...
to the memory. If the memory address consists of M bits, the address area consists of 2^M addresses per chip. Semiconductor memory are manufactured with a certain word length (number of 1-bit cells sharing the same memory address) that power of two, typically M=1, 2, 4 or 8 bit per chip. Consequently, the amount of data stored in each chip is
bits. Possible figures are 1, 2, 4, 8, 16, 32, 64, 128, 256 and 512 bitBit
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...
, kbit, Mbit, Gbit and Tbit, here defined by binary prefix
Binary prefix
In computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
es. By combining several integrated circuits, memory can be arranged for a larger word length and/or address space than what is offered by each chip, often but not necessarily a power of two
Power of two
In mathematics, a power of two means a number of the form 2n where n is an integer, i.e. the result of exponentiation with as base the number two and as exponent the integer n....
.