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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.
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 .
Magnetic sequential access memory is typically used for secondary storage in general-purpose computers due to their higher density at lower cost compared to RAM, as well as resistance to wear and non-volatility. Magnetic tape is a type of sequential access memory still in use; historically, drum memory has also been used.
Time taken to access any record is the same because the same number of nodes is searched; Index is a full index so data file does not have to be ordered; Pros and cons versatile data structure – sequential as well as random access; access is fast; supports exact, range, part key and pattern matches efficiently.
In IBM mainframe operating systems, Basic sequential access method (BSAM) [1] is an access method to read and write datasets sequentially. BSAM is available on OS/360, OS/VS2, MVS, z/OS, and related operating systems. BSAM is used for devices that are naturally sequential, such as punched card readers, punches, line printers, and magnetic tape.
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 computer science, a B-tree is a self-balancing tree data structure that maintains sorted data and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree generalizes the binary search tree , allowing for nodes with more than two children. [ 2 ]
The indexes are created with the file and maintained by the system. IBM supports indexed files with the Indexed Sequential Access Method on OS/360 and successors. IBM virtual storage operating systems added VSAM, which supports indexed files as Key Sequenced Data Sets (KSDS), with more options.