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Secondary storage is non-volatile (retaining data when its power is shut off). Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive. In modern computers, hard disk drives (HDDs) or solid-state drives (SSDs) are usually used as secondary storage.
Off-line bulk storage – Tertiary and Off-line storage. This is a general memory hierarchy structuring. Many other structures are useful. For example, a paging algorithm may be considered as a level for virtual memory when designing a computer architecture, and one can include a level of nearline storage between online and offline storage.
Non-volatile memory is typically used for the task of secondary storage or long-term persistent storage. The most widely used form of primary storage today [ as of? ] is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost.
An illustration of the write amplification phenomenon in flash-based storage devices. Over time, advancements in central processing unit (CPU) speed has driven innovation in secondary storage technology. [7] One such innovation, flash memory, is a non-volatile storage medium that can be electrically erased and reprogrammed.
Partitioned allocation divides primary memory into multiple memory partitions, usually contiguous areas of memory. Each partition might contain all the information for a specific job or task . Memory management consists of allocating a partition to a job when it starts and unallocating it when the job ends.
Volatile memory has several uses including as primary storage. In addition to usually being faster than forms of mass storage such as a hard disk drive , volatility can protect sensitive information, as it becomes unavailable on power-down.
Single-level storage (SLS) or single-level memory is a computer storage term which has had two meanings. The two meanings are related in that in both, pages of memory may be in primary storage or in secondary storage (disk), and that the physical location of a page is unimportant to a process.
For these reasons it is used for primary storage, to hold the program and data the computer is currently working on, among other uses. As of 2017 [update] , sales of semiconductor memory chips are $124 billion annually, accounting for 30% of the semiconductor industry . [ 6 ]