file processing and external sorting earlier presented basic data structures and algorithms that operate on data stored in main memory some applications require that large amounts of information be stored and processed -so much information that it cannot all fit into main memory in that casethe information must reside on disk and be brought into main memory selectively for processing you probably already realize that main memory access is much faster than access to data stored on disk or other storage devices the relative difference in access times is so great that efficient disk-based programs require different approach to algorithm design than most programmers are used to as resultmany programmers do poor job when it comes to file processing applications this presents the fundamental issues relating to the design of algorithms and data structures for disk-based applications we begin with description of the significant differences between primary memory and secondary storage section discusses the physical aspects of disk drives section presents basic methods for managing buffer pools section discusses the java model for random access to data stored on disk section discusses the basic principles for sorting collections of records too large to fit in main memory computer technology changes rapidly provide examples of disk drive specifications and other hardware performance numbers that are reasonably up to date as of the time when the book was written when you read itthe numbers might seem out of date howeverthe basic principles do not change the approximate ratios for timespaceand cost between memory and disk have remained surprisingly steady for over years