Semiconductor memory

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A semiconductor memory is a data memory that consists of a semiconductor .

Microelectronic memory structures are implemented in and on a semiconductor crystal so that a memory chip (see also Die ) is created. The chips are completed to form integrated circuits or processed further without caps.

The data are stored in the integrated circuits in the form of binary electronic switching states . Its predecessors were the magnetically operating core memories , which were not replaced by semiconductor memories until the early 1970s. More recent developments aim to combine the magnetic storage principle microelectronically into high-density, non-volatile memories ( MRAM ).

Storage cell

Various semiconductor memories


A memory cell is the physical realization of the smallest unit of a memory of logical states. The term depending on the context, either the realization of the smallest unit, the 1- bit - storage element , or the realization of the smallest addressable , that is in an access readable or writable, unit, a so-called word or data word consisting of n bits exists (n> 1).

Nowadays, personal computers work with a word length (also called “word width”) of 32 or 64 bits. In the past, for example in the first pocket calculators , memory cells were 4 bits (a half-byte or nibble ) in size. The first PCs, on the other hand, had 8-bit wide memory cells. For simple controls (see: Microcontroller ) 8 bits are still used today.

Word widths of 6 or 7 bits were also used in earlier computers , since alphanumeric processing could be carried out with 64 or 128 storable characters . However, these memories were not yet implemented as semiconductor memories. The Hollerith punch card had a word length of 12 bits.

The memory cells are divided into volatile and non-volatile memory cells. The information is permanently retained in non-volatile memory cells, even if the power supply is interrupted. In the case of volatile memory cells, the information is lost in such a case.


The 1-bit memory element can be implemented using fewer transistors and capacitors . In the case of analog memory cells, the elementary memory component is the capacitor, and in the case of digital memory cells, one (1-T DRAM ) or more transistors are required, e.g. B. with static RAM or with feedback transistors, the so - called flip - flops .

Random access

Memory cells are arranged in a 2 R × 2 C matrix. The memory cells are addressed and written to or read out via word lines and bit lines. A row and a column decoder are required for this. This enables direct access to any memory cells ( random access ). Therefore this arrangement is called Random Access Memory (RAM).

Sequential access

Addressing takes place here using commands, similar to hard drives . The CompactFlash (CF) and PCMCIA designs use e.g. B. the tried and tested ATA / ATAPI command set for hard disks .

This type of addressing requires fewer contact areas on the chip, making it cheaper to manufacture.

See also: memory card , sequential access

Semiconductor memory types

Family tree of semiconductor memory
1 A PLE corresponds to an MROM and vice versa
2 Microcontrollers with MROM are still produced in large numbers (as of the end of 2008).
Meaning of the most important abbreviations
abbreviation meaning
R.A.M. Random Access Memory
ROME Read-only memory
DRAM Dynamic RAM
PRAM Phase-change RAM
MRAM Magnetoresistive RAM
M ... Mask programmed
P… Programmable
EP ... Erasable and programmable
EEP ... Electrically erasable and programmable
SD Synchronous Dynamic (RAM)
GDR Double data rate (RAM)
QDR Quad Data Rate (RAM)
ODR Octo Data Rate (RAM)
GDDR Graphics DDR (RAM)
E.g. SRAM Zero Bus turnaround SRAM
Symbol support vote.svg in production
Symbol oppose vote.svg production stopped
Symbol neutral vote.svg in development

Sales figures

The following table gives an overview of the different memory types (the sales figures given relate to the year 2005 and are taken from the Elektronik Scout 2006; SRAM does not stand for SRAMs contained in processors.):

Sales figures for semiconductor memory components in 2005 (source: Elektronik Scout 2006)
Storage technology sales
Volatile memory (RAM)
Static RAM ( SRAM ) $ 2 billion
Dynamic RAM ( DRAM ) $ 27 billion
Non-volatile memory
Mature material Read Only Memory ( ROM ) $ 2 billion
Flash NAND $ 8 billion
NOR $ 9 billion
Innovative material $ 0.01 billion
Total sales $ 48 billion

Manufacturer (selection)

See also

Web links

Individual evidence

  1. Advances in MRAM technology ( Memento of the original from April 13, 2016 in the Internet Archive ) Info: The @1@ 2Template: Webachiv / IABot / archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved September 30, 2010.