According to DIN 44300, an electrical or electronic memory is a functional unit in a digital computing system that records, stores or outputs data and commands. Electronic memories can be classified according to various criteria, areas of application and characteristic values. For example, according to the storage technology, the storage medium and the associated storage method, the storage organization and the area of application in computer and information technology.
Classification of electronic memories according to storage mediumThe range of storage media is determined by historical development and areas of application. An essential aspect can be seen in the storage of data that can be retrieved in the short term and data that can be used in the long term. While in the fifties of the last century the short-term retrievable data for program execution was stored in relays, flip-flops and core memories, long-term usable data was stored as punched tape or punched card on paper or cardboard, which was later replaced by magnetic technologies such as disk storage, magnetic tapes, hard disks or floppy disks. access times and supply voltages. In parallel, optical storage media such as compact discs, DVDs and Blu-Ray discs were developed for long-term storage.
Classification of electronic memories according to memory technologyThere are various technological differences in semiconductor memories, which are expressed in the fact that certain semiconductor memories can only store the stored data for a short period of time or for a longer period of time by regular refreshing. Other technologies can store their charge permanently without regular refreshing. Therefore, a distinction is made between volatile and non-volatile, dynamic and static memories. With volatile memories, the data is lost when the supply voltage is switched off. The memory content can only be saved by the constant supply of a buffer battery. In contrast, the data in a non-volatile memory continues to be stored even after the supply voltage is switched off, without any special measures being required.
In terms of the organizational form of memories, a general distinction is made between word-organized memories and block-organized memories. Both organizational forms can work with different access methods such as random, quasi-random, direct, implicit or sequential access. Dynamic memories work with random access in which each memory cell is directly accessible. In contrast, static memories operate with fixed memory states that are lost only when signals are applied or when the supply voltage fails.