An example would be a payroll file since each person receives a pay cheque every pay period. If you have 20 files, and you need to access file 18, you must read through files 1 to 17 first. Magnetic tapes are the commonly used here. Information can be accessed sequentially or directly. It is well suited for applications that only process a small portion of the file at any given time.
Hard drives are a good example.
While storing data sequentially, it provides direct access to specific records through an index. This results in quick data access regardless of whether records are being accessed sequentially or randomly. There are a number of products that provide ISAM access for different operating systems and program languages. The main storage device is the hard drive. It contains everything from the operating system, application software, utilities, and files for on going work.