Editing ISAM (section)

==OpenVMS==
The [[OpenVMS]] operating system uses the [[Files-11]] file system in conjunction with RMS ([[Record Management Services]]). RMS provides an additional layer between the application and the files on disk that provides a consistent method of data organization and access across multiple 3GL and 4GL languages. RMS provides four different methods of accessing data; sequential, relative record number access, record file address access, and indexed access.

The indexed access method of reading or writing data only provides the desired outcome if in fact the file is organized as an ISAM file with the appropriate, previously defined keys. Access to data via the previously defined key(s) is extremely fast. Multiple keys, overlapping keys and key compression within the hash tables are supported. A utility to define/redefine keys in existing files is provided. Records can be deleted, although "garbage collection" is done via a separate utility.