On the basis of data is stored in the memory and there access approach . There are four type of access Methods
1. Sequential Access Methods
2. Direct Access Methods
3. Random Access Methods
4. Associative Access Methods
1. Sequential Access Method:
Memory is organised into units of records, called record and each record is associated with address. In sequential access method access must be made in linear sequence. A shared read write mechanism is used and for access we traverse through all locations starting from the current location to desired location , passing and rejecting all the intermediate records until target record is not found. Magnetic tape is the example where sequential access method is used. In Simple Data Structure Linked List is the example of Sequential access.
2. Direct Access:
In direct access data is read immediately without iterating from the beginning. With the sequential access, direct access involves shared read write mechanism and a unique address is assigned to each data or records. Access is made by using this address and data or record is accessed immediately without sequentially searching the complete block of memory. Disk are of Direct Access.
3. Random Access:
Random Access is transferring information to or from memory in which every memory location can be accessed directly rather than being accessed in a fixed sequence. In Random Access Each record or addressable location in memory has a unique address. So any location can be selected at random and directly accessed and addressed. Example: Main Memory and Cache Systems
4. Associative Access:
In this method an access is made by specifying something about the contents of the desired location rather than by using a normal address. An associative memory provides the searching mechanism which searches on the basis of partial memory content or on whole word match. Associative memory is also called as content addressable memory. Cache Memory may use associative access.