Computer access refers to the ability to use a computer, program, network, or website. Access methods include log-in credentials and software routines for storing, retrieving, transmitting, and modifying data. Different access modes are used for different systems, such as sequential access for tapes and indexed access for disks. Local area networks use token passing or CSMA/CD protocols.
Computer access can refer to the ability to use a computer, program, network, or website. An access method may be the appropriate protocol to allow any of these operations. Alternatively, an access method may be a software routine involved in storing, retrieving, transmitting or receiving data, or tracking and, if possible, modifying a failed data transfer.
As for the first meaning, the access mode is often a log-in using an authorized username and password. A smart card keyboard, on the other hand, might require not only the smart card, but also a username and password to create a two-factor authentication login method. Alternative methods may be used on websites. OAuth is an open protocol for authentication that allows only authorized users access to private information.
As for the second meaning, there are different access modes for different systems. For tapes, the sequential access method (SAM) is used. In this method, data is kept in sequential order, ascending or descending, based on a specified key field. SAM compares records for verification.
Indexed access methods are used for disk access, often the indexed sequential access method (ISAM). While the data is stored sequentially, as in SAM, an index is also created where references to records are stored sequentially by start date. An index of key fields is also maintained so that they can be accessed directly.
There are several access methods for local area networks (LANs), including token passing and CSMA/CD (Carrier Sense Multiple Access/Collision Detection), which use the first two layers of the seven-layer Open System Interconnection (OSI) protocol . For mainframes, other methods are used, taking advantage of other layers outside the OSI model.
The CSMA/CD access method begins by checking if the network is silent and, if necessary, waiting for it to be. If collisions are detected, the device and network both wait to try again. When the Ethernet station sends a data frame, the transceiver must make an address match to forward the frame. In token passing, a repeated 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 address.
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