Non-volatile random-access memory

NVRAM (abbr.: Non-Volatile Random Access Memory) is a non-volatile electronic data storage, which is based on random access memories and the data content is maintained without external power supply.

Conventional RAM memory such as dynamic RAM (DRAM ) or static RAM (SRAM ) have no extra precautions to volatile ( volatile ) behavior and lose in case of loss of external power supply the data content.

Species

A common method of forming an NVRAM, is the combination of a conventional nonvolatile RAM memory with an energy store in the form of a battery, an accumulator, or a double-layer capacitor with very high electrical capacity. The energy storage device, also referred to as a buffer battery, provides power for a certain time for the data retention of RAM available. Typically are employed as the SRAM memory cells. Unlike DRAM memories, which need a continuous refresh ( engl. refresh) of the memory cell, the SRAM requires very little power to retain data.

SRAM devices in CMOS technology have the static - in other words in the non-active - state is maintained in which the memory content, a very low power consumption in the range of a few nanoamps to which can be supplied by lithium batteries. Lithium batteries have a low self-discharge over periods of over 10 years ensuring data retention. With compact design, the battery and the SRAM memory can be summarized in one chip package as an NVRAM device.

In addition to the combination of back-up batteries with conventional SRAM memories there are NVRAM technologies which are based on different physical effects such as ferroelectricity. Here, the memory content is written into memory cells, which can hold its bi-stable state is without power supply. Examples of this class of NVRAM are:

In most of these new approaches is attempted, similarly to the DRAM cells, the information stored in a small capacitor to make the charge storage means. Furthermore, even with special semiconductor materials such as silicon carbide (SiC ) is trying to realize bistable NVRAM cells (these technologies are still in the research stage ), which are supposed to guarantee the memory contents over a million years at room temperature for a long time.

As non-volatile memory may be used in addition to an electrically NVRAM or more times programmable EEPROM, flash memory or EPROMs. NVRAM themselves off by the following functional differences:

  • In NVRAM writing any new memory contents without the need of the previous erasure of the memory is performed.
  • In NVRAM writing a new value is the same speed as the read operation. It must be observed when writing any programming sequences and additional wait cycles.
  • The number of write operations is not limited, and the NVRAM are usually set up by the storage structurally unsegmented.

Applications

Application of NVRAM are wherever small, variable amount of data, such as configuration data, starting from a number of 10 bytes to a few megabytes, a long time is to be stored without any external energy supply. A typical application is the personal computers as a CMOS RAM designated NVRAM dar. The imprecise concept is caused by linguistic inaccuracies. In this NV- SRAM the BIOS parameters and hardware configuration of a computer system are stored.

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