What is required for retrieving a record using the Indexed Sequential Access Method (ISAM)?

When retrieving a record using the Indexed Sequential Access Method (ISAM), the process typically involves accessing the index to locate the appropriate data block efficiently and then retrieving the actual record from that block.

In this method, the first step is to access the index, which allows you to pinpoint the location of the desired record. This is the initial disk access. Once the index has been used to locate the specific block where the record resides, the next step is to perform a second disk access to read the data from that block. Thus, a total of two disk accesses are required: one to access the index and another to retrieve the record itself.

This two-step approach highlights how ISAM combines the efficiency of indexing with the sequential processing of data. It allows for quicker lookups compared to purely sequential access methods while minimizing the number of required disk reads.