NUMBER OF REMOTE BATCH TERMINALS
3.2.8 FILE MANAGEMENT SYSTEM (FMS)
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Access the next record or a specified record in a fi Ie Insert or modify a record in a fi Ie
Skip to the first record of the next block from any position in the current block Delete records from fi les
Move to the next volume of a mul ti -volume fi Ie Note his current position in a file
Positi on a fi I e at a specified place
Send specific commands such as page skipping on the printer and forward and backward skip-pi ng on magneti c tape to certai n types of devi ces
• Select a partition in accessing files with partitioned organization
• Insert a new principle partition identifier in the index of a partitioned file
• Read and wri te phys i ca I records
• Check the completion of I/O operations
3.2.7.6 Debug Control
XOS debug controls provide the user with a means of displaying selected parts of his program or data during the execution of his program. The display may be produced conditionally or uncondi-tionally. Monitor services are available to set up the conditional tests.
3.2.7.7 Miscellaneous Services
Included in the miscellaneous procedures are those that: provide the time and date; set and check interval timers; provide user communication with the operator; set, reset, and check the 32 pseudo keys; put a program in the wait or idle state.
3.2.8 FILE MANAGEMENT SYSTEM (FMS)
The File Management System consists of a collection of monitor services which provide the con-nection between user programs and their associated data files and the easy reading and writing of these fi I es by the programs.
Services available through FMS optimize the global data flow of the installation - inputs and out-puts move through buffers and peripherals operate in asynchronous ways in connection with waiting queues managed by the monitor. A complete simultaneity is thus achieved between internal proces-sing and an unlimited number of I/O operations. The system uses chains of I/O requests. One I/O operation may be started as soon as another is finished without disturbing the CPU. This eliminates;
all waiting, realizes a maximum simultaneity of the processing, and best uses the peripherals.
3.2.8.1
Fi Ie OrganizationsThrough FMS, the user may organize his files in any of the following ways:
• Sequential organization: Records are written one after the other sequentially on the medium.
Magnetic tapes may use only the sequential mode
• Indexed sequential: An indexed sequential file consists of a sequential file together with indexes. The indexer permits quick access to a record of data and the sequential format per-mits rapid sequential processing.
• Direct organization: In this organization, a file is considered as a group of blocks, each block being directly accessible if its position, relative to the beginning of the fi Ie, is known
• Partitioned organization: A partitioned fi Ie consists of several sequential groups of records.
The file also contains a directory containing the name and beginning location of each group.
The names in the directory are sorted in alphabetical order.
Disk files may use any of the above organizations. Tape files may use only the sequential organi-zati on.
3.2.8.2
Fi Ie Access MethodsXOS provides both assisted and unassisted access to the files described in the preceding section. In assisted access, the monitor supplies automatic blocking, deblocking, and buffering. In the un-assisted modes, none of these services are provided.
Assi sted access methods:
• Sequential - this method enables the reading or writing of sequential records
• Indexed Sequential - this method enables the creation of an indexed fi Ie, access to records in that file according to their keys or sequentially,and updating of the file with modification, deletion, and insertio n of records
• Partitioned - this method provides direct access to the beginning of a file partition. Once the beginning of the partition is found, the data records within the partition may be processed using the same macro instructions used in the assisted sequential access method
Unassi sted Access Methods:
• Sequential - unassisted sequential access allows the reading and writing of physical records in any fi Ie
• Virtual Direct - this method, which can be applied only to direct access devices, allows reading or writing of physical records of any length, always beginning on a block boundary
• Real Direct - this method, which also can be used only with direct access devices, allows the reading or writing of data starting with a real disk address
3.2.8.3
Other F MS FeaturesFMS supports removable volume. These physically are removable disk packs and reels of magnetic tape which are identified by serial numbers. The serial numbers are written on visible labels on the volume as well as being recorded on the volume by a FMS service routine. The following types of volumes may exist in the system.
• Private volumes - this is a removable volume belonging entirely to one user
• Publ ic or common volumes - a removable volume whi ch can be used by any user for fi Ie creation. The creation of a permanent file on a public volume transforms the public volume into a private volume. The creation of a temporary file will not cause this transformation. At the end of their use in a job, public volumes carrying temporary files are automatically re-turned to the system and are avai labl e for use by others
• Accounting volumes - a removable volume used by the system for the retention of accounting data. The serial number of the accounting volume is permanently known by the system.
On both magnetic tape and disk, FMS supports the following organizational structures:
• Monofi Ie, monovolume
• Monofile, multivolume
• Multifile, monovolume
• Multifile, multivolume
Magnetic tape labels associated with volumes and files contain specific information about the file and the volume. The labels and volume structures conform to USASI norms. Magnetic tapes may also have non-standard labels or no labels at all.
Labels on magnetic disk contain:
• A volume label with volume number and owner number if necessary
• An allocation table representing the disk: space available on this volume
• A table containing file labels which describe the placement of files on this volume
Disk packs may also have no labels or non-standard tables.