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The term computer memory refers to the parts of a Digital Computer which retain physical state ( Data ) for some interval of Time . In its most common usage, "memory" refers to very fast storage which does not retain its stored data when the power is turned off. Compare this to "storage", such as Hard Drive space, which is slow but keeps its data even without power. An analogy is to think of the storage as human memory, with the hard disk as Long-term Memory , and the memory as Short-term Memory . In a Home Computer , memory will often take the form of:
DIFFERENT TYPES AND DIFFERENT PURPOSES Memory can be categorized in different ways by technology or properties:
Historically, "memory" referred to "magnetic core memory" in the 1950 s, and then to semiconductor-based storage in the 1970 s. The evolution of memory is closely tied to the costs of various technologies, as can be seen in the History Of Computing Hardware . Each type of storage is suited for different purposes, and most computers contain several types: primary, secondary, and volatile. Primary vs. secondary storage In traditional parlance, primary storage contains data that are actively being used (for example, the Programs currently being run and the data they are operating on). It is typically high-speed, relatively small, is often (but not always) volatile. It is sometimes referred to as "Main Memory." It can be accessed immediately and randomly. Secondary storage, also known as peripheral storage, is where the computer stores information that is not necessarily in current use. It is typically slower and higher-capacity than primary storage. It is almost always non-volatile. It is slow due to serial access (thus it is also termed Serial Access Memory). Confusingly, these terms are sometimes used differently. Primary storage can be used to refer to local random-access disk storage, which should properly be called secondary storage. If this type of storage is called primary storage, then the term '''secondary storage''' would refer to offline, sequential-access storage like tape media. This usage usually occurs in contexts where only the slower, larger forms of storage are being discussed. Volatile storage Volatile storage loses its contents when it loses power; non-volatile storage does not. Mutable vs. immutable storage Data stored in mutable storage can be overwritten at any time. Data stored in '''immutable storage''' cannot be overwritten. Systems can be made more secure by storing programs and static data in immutable storage, where they cannot be changed by an attacker. Dynamic data is stored in mutable storage because it must be changed from time to time. Most operating systems store all programs and data on hard disk drives, which are inherently mutable storage devices. File system permissions can be used to make certain areas of the hard disk logically immutable. However, the superuser is normally not affected by these permissions thus allowing some attacks to succeed. Some operating systems, such as Linux, extend this logical immutability so data remains immutable even if an attacker gains superuser access. Attackers may be able to destroy the data but they can't change it. A LIST OF STORAGE DEVICES
Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk. Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information. There are several different types of memory:
A LIST OF MEMORY-RELATED SOFTWARE SEE ALSO
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