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Sequential access compared to random access. 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 ...
Random access compared to sequential access. Random access (more precisely and more generally called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any other, no matter how many elements may be in the set.
A direct-access storage device (DASD) (pronounced / ˈ d æ z d iː /) 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 ]
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]
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.
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.
Virtual Storage Access Method (VSAM) [1] is an IBM direct-access storage device (DASD) file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and now in z/OS.
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 .