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What is an Access Method?

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  • Written By: Mary Elizabeth
  • Edited By: Bronwyn Harris
  • Last Modified Date: 07 December 2016
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    2003-2016
    Conjecture Corporation
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Access with regards to a computer can refer to being able to use a computer, a program, a network, or a website. An access method can be the appropriate protocol for allowing any of these operations. Alternatively, an access method can be a software routine that is involved in the storage, retrieval, transmission, or receipt of data or detecting — and amending if possible — a failed data transfer.

With regard to the first meaning, the access method is often a log-in using an authorized user name and password. A smart card keyboard, on the other hand, may require not only the smart card, but also a user name and password to create a dual-factor authentication access method. On websites, alternate methods may be used. OAuth is an open protocol for authentication that allows only authorized users access to private information.

With regard to the second meaning, there are different access methods for different systems. For tapes, the Sequential Access Method (SAM) is used. In this method, the data is kept in sequential order, either ascending or descending, based on a specified key field. SAM compares records for verification.

For disk access, indexed access methods are used, often the Indexed Sequential Access Method (ISAM). While the data is stored sequentially, as in SAM, an index is also created, in which record references are stored sequentially by initial date. An index of key fields is also maintained so they can be accessed directly.

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There are several access methods for LANs (Local Area Networks), including token passing and CSMA/CD (Carrier Sense Multiple Access/Collision Detection), which use the first two layers of the seven-layer OSI (Open System Interconnection) protocol. For mainframes, other methods are used, taking advantage of other layers off the OSI model.

The CSMA/CD access method begins by checking if the network is quiet and, if necessary, waiting until it is. If collisions are detected, the device and the network both wait to retry. When the Ethernet station sends a data frame, the transceiver must make an address match to forward the frame. In token passing, a repeating frame is the token. To send a message, a device waits for an empty token and fills it with the address and some or all of the data, and all network nodes monitor tokens for their own address.

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