HP OpenVMS Systems Documentation
Guide to OpenVMS File Applications
read-ahead processing: A software option used for
sequentially accessing sequential files using two buffers. One buffer
holds records to be read from the disk. The other buffer awaits I/O
record: A set of related data that your program treats
as a unit.
record access mode: The manner in which RMS retrieves
or stores records in a file. Available record access modes are
determined by the file organization and specified by your program.
record access mode switching: Term applied to the
switching from one type of record access mode to another while
processing a file.
record blocking: The technique of grouping multiple
records into a single block. On magnetic tape, an IRG is placed after
the block rather than after each record. This technique reduces the
number of I/O transfers required to read or write the data, and, in
addition (for magnetic tape), it increases the amount of usable storage
area. Record blocking also applies to disk files.
record cell: A fixed-length area in a relative file
that can contain a record. Fixed-length record cells permit RMS to
directly calculate the record's actual position in the file.
record file address (RFA): The unique address RMS
returns to your program whenever it accesses a record. Using the RFA,
your program can access disk records randomly regardless of file
organization. The RFA is valid only for the life of the file, and when
an indexed file is reorganized, each record's RFA will typically change.
record format: The way a record physically appears on
the recording surface of the storage medium. The record format defines
the method for determining record length.
record length: The size of a record in bytes.
record locking: A facility that prevents access to a
record by more than one record stream or process until the initiating
record stream or process releases the record.
Record Management Services: See RMS (Record Management
record stream: The access environment for reading,
writing, deleting and updating records.
relative file organization: The arrangement of records
in a file in which each record occupies a cell of equal length within a
bucket. Each cell is assigned a successive number, called a relative
record number, which represents the cell's position relative to the
beginning of the file.
relative record number: An identification number used
to specify the position of a record cell relative to the beginning of
the file; used as the key during random access by key mode to relative
reorganization: A record-by-record copy of an indexed
file to another indexed file with the same key attributes as the input
RFA: See record file address.
RMS (Record Management Services): The file and record
access subsystem of the operating system. RMS helps your application
program process records within files, thereby allowing interaction
between your application program and the data.
RMS--11: A set of routines that is linked with
compatibility mode and PDP--11 programs and provides similar features
for RMS. The file organizations and record formats used by RMS--11 are
very similar to those of RMS; one exception is that RMS--11 does not
support Prolog 3 indexed files, which are supported by RMS.
root bucket: The primary routing bucket for an index;
geometrically, the top of the index tree. When a key search begins, RMS
goes first to the index root bucket to determine which bucket, at the
next lower level, is the next link in the bucket chain.
seek time: The time required to position the
read/write heads over the selected track.
sequential file organization: The arrangement of
records in a file in one-after-the-other fashion. Records appear in the
order in which they were written.
sequential record access mode: Record storage or
retrieval that starts at a designated point in the file and continues
in one-after-the-other fashion through the file. That is, records are
accessed in the order in which they physically appear in the file.
shared access: A file management technique that allows
more than one user to simultaneously access a file or a group of files.
stream: An access window to a file associated with a
record access control block (RAB) supporting record operation requests.
stream record format: Property of a file specifying
that the data in the file is interpreted as a continuous sequence of
bytes, without control information, except for terminators that are
recognized as record separators. Stream record format applies to
sequential files only.
synchronous record operation: An operation in which
your program does not regain control until after the completion of a
record retrieval or storage request. See also asynchronous record
terminator: Special characters or character sequences
used to delimit the records in files using the stream record format.
track: A collection of blocks at a single radius on
one recording surface of a disk.
tuning: The process of designing your files to achieve
better processing performance.
user buffer: A buffer within an application program.
variable-length record format: Property of a file in
which record length may vary.
variable-length with fixed-length control field (VFC) record
format: Property of a file in which records of variable-length
contain an additional fixed-length control field capable of storing
data that may have no connection with the other contents of the record.
VFC record format is not applicable to indexed files.
VFC record format: See variable-length with
fixed-length control field (VFC) record format.
volume (disk): An ordered set of 512-byte blocks. The
medium that carries Files--11 On-Disk Structure files.
volume (magnetic tape): A reel of magnetic tape, which
may contain a part of a file, a complete file, or more than one file.
volume set: A collection of related volumes.
write-behind processing: A software option used for sequentially accessing sequential files using two buffers. One buffer holds records to be written to the disk. The other buffer awaits I/O completion.