access method

(communications) The procedures required to obtain access to a communications network.
(computer science) A set of programming routines which links programs and the data that these programs transfer into and out of memory.

A software routine that is part of the operating system or network control program which performs the storing/retrieving or transmitting/receiving of data. It is also responsible for detecting a bad transfer of data caused by hardware or network malfunction and correcting it if possible. See also access mode.

Tape Access Methods

Tapes use the sequential access method (SAM), which keeps records in order by a key field such as account number. Each record must be compared to find the desired one. Although there is no direct access mechanism to each individual record on a tape, modern drives allow fast forwarding to index points where different groups of records can be stored.

Disk Access Methods

Indexed access methods are widely used to keep track of records and files on disk. The index is a table of contents with pointers to the location of each file on the disk or each record within the file. A common approach is the indexed sequential access method (ISAM), which uses an index that is kept in sequential order and points to the records stored in the order that they arrived. The pure sequential method may also be used if direct access is not required. For fastest retrieval, there are various direct access methods that use a formula to convert the record's identifying field, such as account number, into a physical storage address.

Communications Access Methods

Local area network (LAN) access methods, such as CSMA/CD (Ethernet) and token passing (Token Ring), transfer data to and from connected computers on the network. These methods reference layers 1 and 2 of the OSI model.

Mainframe access methods, such as IBM's TCAM and VTAM, transfer data between a host computer and remote terminals. These routines prepare the data for transmission by placing the data into frames with appropriate control codes. These methods reference layers 3, 4 and 5 of the OSI model.

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