Differentiation Between Sequential And Direct/Indexed Data Sets By Common Accessing Software
Original Publication Date: 1979-May-01
Included in the Prior Art Database: 2005-Feb-20
The major barriers to having operating systems with common programming support for sequential, direct and indexed access to data on files are efficiency and execution time. In sequential access, the highest efficiency occurs if the data on the disk are initially unformatted and formatting occurs in the process of storing the data. Therefore, in sequential accessed files, no records empty or otherwise exist between the last record written ("the high water mark") and the end of the area on the storage device allocated for the data set ("data extent"). In direct or indexed access methods, the high water mark (HWM) concept has no meaning and the data extent is preformatted with empty records prior to the first time the data set is used.