OpenVMS Record Management Services

Whereas the basic units used by the file system are files and blocks, Record Management Services (RMS) is concerned with the internal structure of files. Even though programs are allowed to access virtual blocks directly, most programs handle data as collections of records. RMS provides record-oriented services and handles the file system interface on behalf of a program.

RMS provides support for a variety of different file and record formats, many more variations than are found on most operating systems. File formats are typically sequential, indexed, and relative. Records may be of fixed or varying length and possess a variety of carriage-control attributes. A program may use RMS to create a file with certain file and record characteristics and then simply supply records to RMS. RMS handles the organization of records into blocks and makes the appropriate file system calls to store the file on disk. Likewise, when opening an existing file, RMS can interpret the file and record characteristics automatically and supply the data to the program in the form of records.

Most language compilers use RMS to implement their built-in I/O routines, but a programmer may choose to use RMS or the file system (via $QIO) directly. This can provide for more flexibility and, if used properly, superior performance to built-in I/O routines. The programmer should bear in mind, however, that doing so decreases the portability of the program to other operating systems.



Getting Started with OpenVMS(c) A Guide for New Users
Getting Started with OpenVMS: A Guide for New Users (HP Technologies)
ISBN: 1555582796
EAN: 2147483647
Year: 2005
Pages: 215

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