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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.
J/Direct used a kind of annotation in Java code to make the link between Java and Windows functions. As annotations did not exist in Java when J/Direct was designed, Microsoft used a special syntax in Java comments. For example, to declare the GetSysColor function in the User32 API: [3]
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 .
Basic Direct Access Method, or BDAM is an access method for IBM's OS/360 and successors computer operating systems on System/360 and later mainframes. BDAM "consists of routines used in retrieving data from, and storing data onto, direct access devices." [1]: p.5 BDAM is available on OS/360, OS/VS2, MVS, z/OS, and related high-end operating ...
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.
In IBM mainframe operating systems, Queued Sequential Access Method (QSAM) [1] is an access method to read and write datasets sequentially. QSAM is available on OS/360 , OS/VS2 , MVS , z/OS , and related operating systems.
In either case, significant amounts of code to manage records must be provided in protected routines to ensure file integrity. An alternative to a Record-oriented file is a stream file, in which the file system treats a file as an unstructured sequence of bytes. The applications may, but need not, impose a record structure.