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Read-write memory is a type of electronic storage used by computers and other devices that can have information stored on it and, subsequently, can have that same information retrieved later. There are several physical forms of read-write memory, such as computer random access memory (RAM) chips, hard drives, and rewritable compact disks (CD-RWs) to name a few. The purpose of read-write memory can be to permanently store information for later use, such as is the case with a CD-RW, or it can be to provide an area of fast access to information that has been compiled or loaded, as is the case with RAM chips. There is a distinct functional difference between read-write memory, read-only memory (ROM) and write-only memory (WOM).
By far, read-write memory is the most widely implemented type of memory in electronic devices and computers. The system is able to change the information stored at a given address within the memory and also can retrieve information from the memory. This method of computer memory became important as the complexity of computer software advanced and operating systems required progressively larger areas in which to store information and make long calculations.
There are two forms of read-write memory, with the first being static- or storage-type memory. This is a type of memory designed to be written to, and to then retain that information despite not having an active piece of software or electronic signal powering it. Hard disk drives, CD-RWs, flash drives and certain types of embedded circuits all have this capability.
The second form is called volatile memory. This is usually an embedded microchip or other electronic hardware that is able to act as a location where information can be read and written but does not persist without some external power supply or software system. Computer RAM is an example of volatile read-write memory, in which the information stored in the RAM chips becomes lost or irretrievable once the computer is turned off. This type of memory has very fast access times, because it is not physically encoded on a medium.
In contrast to read-write memory are read-only and write-only memory. Read-only memory is frequently used to transfer information on a physical medium in a way so it cannot be modified by a user. It also is used within certain file systems to protect vital areas of the operating system from damage through accidents or malicious software. Write-only memory is usually employed to provide a safe outlet for unneeded information or other signals, such as a virtual hardware port that leads to nothing, called a NUL device, where data can be safely disposed of but never read back.