TOPS-20 User's Guide

Chapter 7 Using magnetic tape

This chapter describes:

Magnetic tape provides off-line storage for data. You put data onto tape for storage using the COPY command, DUMPER program, or a program of your own. (For a complete description of the DUMPER program, refer to the TOPS-20 User Utilities Guide.) Tapes can be labelled or unlabelled. An unlabelled tape is identified only by a gummed label on the outside of the tape reel. A labelled tape is identified by the information contained internally on the tape as well as a gummed label on the outside of the tape reel. Refer to the TOPS-20 Tape Processing Manual for more information on labelled and unlabelled tapes.

Before you use an unlabelled tape, give the INFORMATION SYSTEM-STATUS command to find out if the tape allocation facility of TOPS-20 is enabled. The process to gain and release access to a tape differs, depending upon whether this tape allocation facility is in use. (Refer to the TOPS-20 System Manager's Guide for an explanation of tape allocation.)

If tape allocation is enabled on your system, you can mount an unlabelled tape by giving the MOUNT TAPE command followed by the name of the tape (the name that appears on the gummed label). Before you give the MOUNT TAPE command, tell the operator the name you selected for your tape or ask him to get the tape from the tape library. After you give the MOUNT TAPE command, you must wait until the operator mounts the tape, and the system prints a message telling you that the tape is mounted.

        @MOUNT TAPE (NAME) ACE1:
        [Tape set ACE1, volume ACE1 mounted]
        [ACE1:  defined as MT0:]

You can include the /NOWAIT switch with your MOUNT TAPE command. By including this switch, you do not have to wait for a response from the operator and you can continue working until the tape is mounted. When you use the /NOWAIT switch, you can also check on your mount request by giving the INFORMATION MOUNT-REQUESTS command.

        @MOUNT TAPE (NAME) ACE1: /NOWAIT

If you want to remove the request from the queue before the tape is mounted, type a CTRL/C to return to command level, then give the CANCEL MOUNT command. If you included a /NOWAIT switch with the MOUNT TAPE command, you can simply give the CANCEL MOUNT command.

After the operator mounts the tape, the system sends a message advising you that the tape is ready for your use. You can now run your program.

When you complete your work, give the DISMOUNT TAPE command, followed by the name of the tape. The system prints a message telling you that the tape is dismounted.

        @DISMOUNT TAPE (NAME) ACE1:
        [Tape dismounted, logical name ACE1: deleted]

If tape allocation is not enabled on your system, you must first assign a tape drive for your job. To find out which tape devices are available, give the INFORMATION AVAILABLE-DEVICES command.

        @INFORMATION (ABOUT) AVAILABLE-DEVICES
        Devices available to this job:
         DSK, PS, ADMIN, MTA1, MTA2, LPT, CDR, PTY15, NUL
        Devices assigned to/opened by this job: TTY23

Assign one of the devices beginning with 'MTA'. The example shows assigning drive 2.

        @ASSIGN (DEVICE) MTA2:

After assigning the drive to your job, you can run the PLEASE program and ask the operator to mount your tape.

        @PLEASE
        Enter text, terminate with CTRL/Z to wait for response
        Or ESC to send message and Exit
        Please mount tape TEST:<CTRL/Z>
        [PLSOPN Operator at GIDNEY has been notified at 11:18:32]

        11:36:04 From Operator at terminal 2
             =>Your tape is mounted

        Enter new text (Same terminators)

        Thanks<ESC>

When you complete your work, give the UNLOAD command. This command unloads the magnetic tape by rewinding it entirely onto the source reel.

After you give the UNLOAD command, give the DEASSIGN command. The DEASSIGN command returns the device you had previously ASSIGNed back to the pool of available devices. If you forget to do this, no other user can use the device until you log out.

You must make sure that you read and write the data on the tape with the proper tape parameters set. Give the INFORMATION TAPE-PARAMETERS command.

        @INFORMATION (ABOUT) TAPE-PARAMETERS
         SET TAPE DENSITY 1600
         SET TAPE PARITY ODD
         SET TAPE FORMAT CORE-DUMP
         SET TAPE RECORD-LENGTH 512

These parameters work for most tape transfers; if you have to change any of the parameters, give the SET TAPE command.

        @SET TAPE DENSITY (TO) 800

These changed parameters remain in effect until you log off, or change the parameters.

Not every tape drive supports every parameter. Check with your system manager to find out what drive types are available on your system and which parameters work with each drive type.

If you set a parameter by giving a DUMPER command, that parameter affects only the DUMPER operations and does not change your job defaults. For a complete description of DUMPER, refer to the TOPS-20 User Utilities Guide.

There are commands that position a magnetic tape: BACKSPACE, REWIND, and SKIP. The BACKSPACE command backspaces the tape over a certain number of records or files on unlabeled tapes, and over a certain number of files on labeled tapes; the REWIND command rewinds the tape to the beginning of the tape; the SKIP command advances the magnetic tape a certain number of records or files on unlabeled tapes, and a certain number of files on labeled tapes.

        @SKIP (DEVICE) MTA2: 4 FILES

The operator creates the labelled tapes for you through a process called initialization. When a tape is initialized, the system actually writes specific information on the tape. Included in this information is a volume identifier, also called a VOLID. The VOLID is a unique number assigned to the tape.

Once the operator creates the labelled tape, you can give the MOUNT TAPE command followed by the tape volid or the setname you selected for your tape(s). In the following example, the /NEW switch specifies that you are creating a new tape with the tape setname ABCD:. For a complete list of switches to use with the MOUNT TAPE command, refer to the TOPS-20 Commands Reference Manual.

        @MOUNT TAPE (NAME) ABCD:/NEW
        [Tape set ABCD, volume 002001 mounted]
        [TEST:  defined as MT2:]

After the operator mounts the tape, the system sends a message advising you that the tape is ready for your use and which drive you have been assigned. You can now run your program.

If your program requires additional tapes to complete the job, the operator will automatically mount the additional tapes. The system does not notify you of the volids of the additional tapes. To find out the volids of the additional tapes you can give the INFORMATION VOLUMES command, followed by the tape set name to obtain a list of the volume identifiers for each tape in the tape set. In the following example, the tape set name ABCD: contains three tapes with the volids of 002001, 002002, and 002003:

        @INFORMATION (ABOUT) VOLUMES (OF TAPE) ABCD:
        Volumes of tape set ABCD:  002001, 002002, 002003

To read an existing tape set containing several volumes, include the tape setname and the /VOLIDS: switch in the MOUNT TAPE command.

        @MOUNT TAPE (NAME) ABCD:/VOLIDS: 002001,002002,002003
        [Tape set ABCD, volume 002001 mounted]
        [ABCD: defined as MT2:]

You can also mount a specific volume in the tape set by specifying the /START switch followed by the volid for that specific volume. For example, if you want to mount the second volume in the tape set name ABCD:, give the following command.

        @MOUNT TAPE (NAME) ABCD:/VOLIDS:002001,002002,002003  -
        /START:VOLUME 002002
        [Tape set ABCD, volume 002002 mounted]
        [ABCD:  defined as MT0:]

The operator mounts the tape, and the system prints a message telling you that the tape that you requested is mounted.

If you include the /NOWAIT switch in the MOUNT TAPE command you can check on your request to mount the tape, by giving the INFORMATION MOUNT-REQUESTS command. The system prints a list of mount requests in the queue, and indicates the status of the request.

        @INFORMATION (ABOUT) MOUNT-REQUESTS

        Mount Queue:
        Volume     Status   Type  Dens   Write    Req#   Job#   User
        -------   --------  ----  ----  -------  ------  ----  ---------
        MCBFT2    MTA2      Tape  1600             32      18  SROBINSON
        ASDF      MTA3      Tape  defa  Enabled    73      36  KONEN
        002002    MTA0      Tape  6250  Enabled    74       7  SARTINI

        There are 3 requests in the queue

If you want to remove your mount request from the queue, give the CANCEL MOUNT command, followed by the tape setname. You must first give a CTRL/C to get out of the MOUNT command before you can cancel the mount request. If you included the /NOWAIT switch, you can simply give the CANCEL MOUNT command. You can give the CANCEL MOUNT command as long as the request is in waiting status, that is, as long as the operator has not mounted the tape.

        @CANCEL (REQUEST TYPE) MOUNT ABCD:
        [1 mount request canceled]

When you no longer need to access the tape, give the DISMOUNT TAPE command, followed by the tape setname.

        @DISMOUNT TAPE ABCD:
        [Tape dismounted, Logical name ABCD:  deleted]