A RAM-disc is a virtual disk which use part of the main memory of the Ordinateur, the Random access memory, as a mass memory, a function typically carried out by the hard drives. The access times are largely improved, because the random access memory roughly has an access time 100 times shorter than the hard drives. However, the volatility of the random access memory implies that the data will be lost if the supply is cut off, for example when the computer is put not under tension. The RAM-discs can be used for to store temporarily data or to store software some decompressed for one short period of time.

The RAM-discs were usually used as support of starting in the years 1980, when the hard drives were expensive, the readers of slow diskettes and that some systems, in particular those of the series Amiga and the Apple IIgs, were able to start starting from a RAM-disc . At the cost of some modules of random access memory, the computer could then be started again hot in a few seconds instead of a few minutes. Certain systems once had RAM-discs on battery ensuring the persistence of their contents the stopped system.

The use of a Mémoire hiding place for the accesses to the hard drives by the Operating system seems to make useless the recourse to a RAM-disc . A Mémoire hiding place disc fulfills a similar function of rapid access to the data stored on disc, without having the disadvantages of them: loss of data at the time of power cut, partitioning fixes,… the RAM-discs prove however essential in the situations where a physical disc is not available, or when the support of data must remain irremovable (such as for example, for the LiveCD). They can also find their utility in the devices type kiosk where the initial configuration must be charged with each starting and that no reconfiguration of the system is necessary in the course of operation.

The arrival of the hard drives with standard high-flow Serial ATA made it possible the RAM-discs to connect directly like normal hard drives, and this in spite of their rate of extremely fast transfer.

Another technique of use of the random access memory for the storage of files is the temporary Filesystem. Indeed, unlike a RAM-disc seen like a partition fixed disc of capacity, a filesystem temporary increases and decreases by size according to the needs.

The RAM-discs have the advantage of being appreciably faster than the hard drives and require only one special pilot and of course, of the random access memory of the computer. Their disadvantage is that they are limited by the central memory size, and that the data will be lost at the time of power cut, unless an emergency power supply was not provided, like a Accumulator battery, for example.

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