Computing memory

Function of the memory

In electronic numerical, which is the base of data processing, one seeks with Mémoriser a possible Information simplest, generally that is limited to the Binary system, which is satisfied with the presence or not of information.

Various technologies

Condenser

The condensing have like first property to store the electrical energy. They were very early used as memory, but their weak performances confined them a long time with subordinates roles of filtering.

Since progress of the Micro-electronic , it is the capacity of microscopic condensers organized in screens, arranged and managed within electronic chip S which is used as fast numerical memory for the modern Ordinateur S. These integrated circuits specialized names memory Dynamique or DRAM. The large defect is due to the size of the condensers: they are so tiny that information can be preserved intact only some fractions of second. Information thus should permanently be refreshed, which requires additional circuits.

Electronics

With the logical circuits have can manufacture memories (Bascule). The memory thus realized can be classified in two families: SRAM and the ROMANIAN

the SRAM or (Static Random Memory Access) have several defects: they are large consumers of electrical energy, but especially they could not be sufficiently integrated to compete with the dynamic storages with condenser. On the other hand it are famous very fast.

technologies used, for the " memories flash" and other names of memory of pocket, made it possible to briskly exceed the performances of the old SRAM at the price of some concessions at the speed of transfer.

the ROMANIANS or (Read Only Memory) have the advantage of not being volatile: have enters there of the data and they remain intact in absence of food, on the other hand they are slow access and the modification of the data is not for certain models not possible.

New generation

A new generation of memory RAM could combine the advantages of the current DRAM (level of integretion) and SRAM (not Volatilité) and radically improve the performances of these two technologies. To improve the performance of the electronic memories (i.e memories with semiconductors), it is to reduce the number of electrons necessary to the storage of a bit of information. The ultimate goal is thus the Mémoire mono-electronics which would use only one electron (or some electrons) in the place of almost a half-million necessary today to the storage of an elementary bit of information.

Electromechanics

The systems electromechanical S containing relay were among the first reliable systems intended to memorize information.

Since, multiple electromechanical systems are able to record in form Magnétique or Optique of the Donnée S in great quantity: Hard drive, Diskette, DAT, CD-ROM, DVD.

Magnetic core

The technique of the Tore Magnétique used the capacity of a winding on torus of ferrite to store a binary electric information. Associated with an electronic management, the computers had access to a system powerful report, though somewhat cumbersome compared to that of the dynamic storage. It has on the other hand had an enormous advantage, for a few decades, thanks to the reduction in consumption; this type of circuit can store these information during several years thanks to incorporation in the integrated circuit of Battery providing an energy of safeguard.

Operation of the memories

Various functions of the memory

The memories can be divided into several families according to their functions:

the memory-register is integrated into the processor. This type of memory is very fast but also very expensive and thus is reserved for a very small quantity of data.
the Random access memory allows the processor and the additional controllers to store in a temporary way the data essential to their operation but nevertheless in a way less dependant on the microprocessor.
the Read-only memory provides to these same data-processing components the invariable data (programs and data) necessary to their starting and, thereafter, with their operation, by storing them in an inalterable way.
the Mass memory constitutes the means of filing the data before and after their data processing; this type of memory is generally slowest of the three but it offers the best cost ratio/quantity of data storage.

A memory is known as remanent when the temporary extinction of the system does not destroy the contents of it. This memory is not always managed like a filing system and is sometimes integrated in same logical space as the random access memory, as in the case of the cellphones but also in “a certain operating system very precise whose study was the complete examination object of Selor (organization of federal recruitment Belgian) and who was the FIRST to propose a virtual addressing and in which the hard drives seemed random access memory”.

The data processing schools insist more on the concept of Bus of Data bus address and (concept of Adressage report) which does not apply in the same way to the mass memories.

Memory and operating systems

The memories can be seen like the continuity of fastest and most expensive with the memory slower and least expensive.

Registers of the Processor,
Mémoire hiding place,
Mémoire general use,
Mémoire of storage.

Hierarchy of memory

The access report, the Effectiveness of the mask and the transfers between the various levels of the hierarchy of the memory become an important limit of the speed of the machine. The Processeur can be found to wait until the transfers of memory are achieved.

The various memories are characterized mainly by:

access time (or the time put by the system to reach or write the data);
the Price;
capacity with being modified (writing and rewriting);
obstruction;
the electric Consumption ;
the Time of conservation of Given S.

Characteristics of the computing memories:

Address: numerical value indicating a physical element of memory.
Capacity or memory size: quantity of Information S which it can contain. One can express it according to number of Bit S, Octet S (or bytes), or of Mot S,
Access time: Time which runs out between a request for Lecture or of writing and its achievement.
Cycle report: minimum Time between two consecutive accesses longer than the access time, because the good performance of the memory requires some operations of maintenance, of stabilization of signals…
Débit: many bytes or bits being able to be read or written a second (example 12 Mo/s).
Volatility: loss or not of the contents, a volatile memory loses its contents when the current is shut off. (RAM: bird, if one shuts off the current all is lost at once; magnetic band: loss after 5 years).

References

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