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Direct-access storage device. A direct-access storage device ( DASD) (pronounced / ˈdæzdiː /) is a secondary storage device in which "each physical record has a discrete location and a unique address". The term was coined by IBM to describe devices that allowed random access to data, the main examples being drum memory and hard disk drives. [1]
The term "ROM" is sometimes used to refer to a ROM device containing specific software or a file with software to be stored in a writable ROM device. For example, users modifying or replacing the Android operating system describe files containing a modified or replacement operating system as "custom ROMs" after the type of storage the file used ...
When used within a robotic tape library, it is classified as tertiary storage instead. Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. [1] : 15–16.
Direct memory access (DMA) is a feature of computer systems that allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). [1] Without DMA, when the CPU is using programmed input/output , it is typically fully occupied for the entire duration of the read or write operation, and is thus ...
Direct-attached storage. Direct-attached storage ( DAS) is digital storage directly attached to the computer accessing it, as opposed to storage accessed over a computer network (i.e. network-attached storage ). DAS consists of one or more storage units such as hard drives, solid-state drives, optical disc drives within an external enclosure.
Network-attached storage ( NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the technology and systems involved, or a specialized device built for such functionality (as unlike ...
Layer 0. Physical. A storage area network ( SAN) or storage network is a computer network which provides access to consolidated, block-level data storage. SANs are primarily used to access data storage devices, such as disk arrays and tape libraries from servers so that the devices appear to the operating system as direct-attached storage.
Since the access time depends on the physical location of the data on the device, mechanically addressed systems may be sequential access. For example, magnetic tape stores data as a sequence of bits on a long tape; transporting the tape past the recording head is required to access any part of the storage. Tape media can be removed from the ...
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