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Indexed Sequential Access Method (ISAM) is a method for creating, maintaining, and manipulating computer files of data so that records can be retrieved sequentially or randomly by one or more keys. Indexes of key fields are maintained to achieve fast retrieval of required file records in indexed files .
Sequential access is a term describing a group of elements (such as data in a memory array or a disk file or on magnetic-tape data storage) being accessed in a predetermined, ordered sequence. It is the opposite of random access , the ability to access an arbitrary element of a sequence as easily and efficiently as any other at any time.
versatile data structure – sequential as well as random access; access is fast; supports exact, range, part key and pattern matches efficiently. volatile files are handled efficiently because index is dynamic – expands and contracts as table grows and shrinks; less well suited to relatively stable files – in this case, ISAM is more efficient
MS-DOS, for example, used a simple File Allocation Table (FAT). The FAT has an entry for each disk block, [note 1] and that entry identifies whether its block is used by a file and if so, which block (if any) is the next disk block of the same file. So, the allocation of each file is represented as a linked list in the table.
Non-Shared Resources (NSR), which is optimised for sequential access. NSR access has historically been easier to use than LSR for batch programs. [12] Distributed File Management (DFM), an implementation of a Distributed Data Management Architecture server, enables programs on remote computers to create, manage, and access VSAM files.
In computing, a file system or filesystem (often abbreviated to FS or fs) governs file organization and access. A local file system is a capability of an operating system that services the applications running on the same computer. [1] [2] A distributed file system is a protocol that provides file access between networked computers.
In computing, sequential access memory (SAM) is a class of data storage devices that read stored data in a sequence. This is in contrast to random access memory (RAM) where data can be accessed in any order. Sequential access devices are usually a form of magnetic storage or optical storage. [1] [2]
An indexed file is a computer file with an index that allows easy random access to any record given its file key. The key must be such that it uniquely identifies a record. If more than one index is present the other ones are called alternate indexes. The indexes are created with the file and maintained by the system.