What’s Dynamic RAM?

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DRAM is a common computer memory that can hold a lot of data in a small space but doesn’t retain data when power is off. It needs constant power to work and is cheaper than Flash memory. DRAM and SRAM are used together, with DRAM used for larger capacities and SRAM for caching. While it’s difficult to access DRAM after a power outage, it questions the reliability of security measures that store encryption keys in DRAM.

Dynamic Random Access Memory, or DRAM, is the most common type of computer memory. It is especially useful for computers as it can hold a lot of data in a small physical space. However, it usually doesn’t retain data when the power is off, which means it’s not suitable for permanent storage.

Random access memory simply refers to memory where any data can be accessed almost instantly. This is in contrast to storage media such as cassettes where the data can only be accessed in a fixed sequence. The “dynamic” element of DRAM is that its power supply must be constantly updated for it to work. This distinguishes it from static random access memory or SRAM.

Both SRAM and DRAM work by holding information in binary format, which means it is split into 1s and 0s. With static random access memory, this is done via an electric current that can be switched in two different directions. With dynamic random access memory, this is done by a series of cells that are full of electrons or empty. However, all cells self-discharge almost instantly and therefore need to be recharged constantly.

Most computers use the two types of memory together. Generally dynamic random access memory is used in larger capacities because it is much more space efficient and therefore cheaper. Static random access memory, which is faster to access but less space efficient, is usually used for caching. This involves storing the data the computer is most likely to need during operation, reducing the number of times the computer has to access slower DRAM.

Because dynamic random access memory needs power to keep filling up cells, it usually can’t store data once the power goes out, such as when the computer is turned off. This is different from forms of memory such as Flash which are used for memory cards and solid state drives. This is one reason why DRAM is so much cheaper than a Flash memory card of the same capacity.
The way dynamic random access memory works ensures that, when functioning properly, it will continue to hold data as long as the power allows it to fill cells. However, it doesn’t work the other way around: there’s no guarantee that the power outage will erase the memory. While extremely difficult to do in practice, there are several theories as to how the memory of a computer that has been shut down could be accessed, such as by freezing the memory chip and moving it to another machine. This questioned the reliability of some security measures that encrypt a hard drive and store the encryption key in DRAM.

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