The File System The Conversational Monitor System interfaces with virtual disks, tapes,
and unit recordequipment. The CMS residence device is kept as a
read-only, shared,system disk. Permanent user files may be accessed from up to nine active disks. Logical access to those virtual disks is
controlledby CMS, while CP facilities manage the device sharing and
virtual-to-real mapping.User files in CMS are identified with three designators. The first
is filename. The second is a filetype designator thatmay imply specific file characteristics to the CMS file .anagement routines$ The
third is a filemode designator that describes the location and accessmode of the file.
The compilers available undereMS default to particular input
filetypes, such asASSEMBLE, but the file manipulation and listing
commands do not. Files of a particular filetype form a logical data
library for a user; for example, the collection of allCOBOL source
files, or of all object(TEXT) decks, or of all EXEC procedures. This
allows selective handling of specific groups of files with minimum inputby the user. User files can be created directly from the terminal with the CftS EDIT facility. EDIT provides extensive context editing services. Pile characteristics such as record length and format, tab locations, and
serialization options can be specified. The system includes standard
definitions for certain filetypes.eMS automatically allocates compiler work files at the beginning of command execution on whichever active disk has the greatest amount of
available space, and deallocates them at completion. Compiler object
decks and listing files are normally allocated on the same disk as the
input source file or on theprimary read/write disk, and are identified by combining the input filename with the filetypes TEXT and LISTING. These disk locations may be overridden by the user. 1 single user file is limited to a maximum of 65533 records and must reside on one virtual disk. The file management system limits the number of files on anyone virtual disk to 3400. All CftS disk files are
written asaOO-byte records, chained together by a specific file entry
that is stored in a table called theMaster File Directory; a separate Master File Directory is kept for, and on, each virtual disk. The data
recordsmay be discontiguous, and are allocated and deallocated
automatically.1 subset of the Master File Directory (called the User File Directory) is made resident in virtual storage when the disk
directory ismade available to CMS; it is updated on the virtual disk at
least once per command if the status ofany file on that disk has been
changed.Virtual disks may be shared by eMS users; the facility is provided by YM/370 to all virtual .achines, although a user interface is directly
available inCMS commands. Specific files may be spooled between
virtualmachines to accomplish file transfer between users. Commands allow such file manipulations as writing from an entire disk or from a
specific disk file to a tape, printer, punch, or the terminal.Other commands write from a tape or virtual card reader to disk, rename files,
copy files, and erasefiles.· Special macro libraries and text or program libraries are provided by CMS, and special commands are provided
to update and use them.eMS files can be written onto and restored from unlabeled tapes via CMS commands. Multiple write access under eMS can produce unpredictable
results.
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and unit record
read-only, shared,
controlled
virtual-to-real mapping.
is filename. The second is a filetype designator that
third is a filemode designator that describes the location and access
The compilers available under
filetypes, such as
commands do not. Files of a particular filetype form a logical data
library for a user; for example, the collection of all
files, or of all object
allows selective handling of specific groups of files with minimum input
serialization options can be specified. The system includes standard
definitions for certain filetypes.
available space, and deallocates them at completion. Compiler object
decks and listing files are normally allocated on the same disk as the
input source file or on the
written as
that is stored in a table called the
records
automatically.
directory is
least once per command if the status of
changed.
available in
virtual
specific disk file to a tape, printer, punch, or the terminal.
copy files, and erase
to update and use them.
results.
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