MAGSTRU -- Mag Tape Structure Report

Prints out a report of the record and file structure on a magnetic tape.

MAGSTRU is a tape utility and does not actually read any data from tape. It is useful in getting a quick overview of the structure of an unknown tape on systems where there is no operating system utility available for this action.

PARAMETERS

MAGSTRU is controlled by the following global parameters: 

Name     Prompt                                  Count     Type
REPORT   Report mode: TERM/OFF/filename          1-64      Char

REPORT

Specifies the file to which to append the generated report. 

 EASI>REPORT="filename"
The following names have special meaning 

 EASI>REPORT="TERM"     | generates reports on your terminal
 EASI>REPORT="DISK"     | generates reports on file "IMPRPT.LST"
 EASI>REPORT="OFF"      | usually cancels report generation, but
                        | MAGSTRU forces REPORT to terminal output

DETAILS

MAGSTRU is a simple tape utility used to decode and dump the record and file structure of a magnetic tape to the report device (REPORT). This capability may also be available as a standard operating system utility, in which case it may be better to use it instead of MAGSTRU.

The most important use of MAGSTRU is in attempting to read unknown and unsupported tape formats. When used in conjunction with PACE programs MVB and MIB, as well as some common sense and imagination, image data can usually be read off tape.

Other useful operating system level utilities which can help are: 

 UNIX:          dd, od, mt, tcopy       (unix commands)
 VAX VMS:       dump                    (VMS utility)
Check the on-line help on your system or the documentation for more information on these commands.

EXAMPLE

The user has a 9-track 1/2-inch magnetic tape which is claimed to contain imagery. Annoyingly, there is no indication of the tape format and no way to contact the original producer of the tape. The initial action is to mount the tape and run the PACE program MSH to see if MSH could determine the format of tape automatically and indicate which PACE tape reading program to run. Unfortunately, MSH cannot determine the tape format, so it is up to the operator to spend time attempting to read the tape using imagination, experience, determination, and any available tape utilities. 

 EASI> REPORT="TERM"
 EASI> RUN MAGSTRU

    5 records of   80 bytes
      ***  EOF ***
   64 records of 16384 bytes
      ***  EOF ***
    4 records of   80 bytes
      ***  EOF ***
    4 records of   80 bytes
      ***  EOF ***
   64 records of 16384 bytes
      ***  EOF ***
    4 records of   80 bytes
      ***  EOF ***
    4 records of   80 bytes
      ***  EOF ***
   64 records of 16384 bytes
      ***  EOF ***
    4 records of   80 bytes
      ***  EOF ***
      ***  EOF ***
This report shows there are quite a number of files on the tape; however, most of them are very small (4 or 5 records of 80 bytes each). Files of this sort tend to be header files or annotation files containing information describing the imagery, or they may be special information produced by the operating system of the computer which produced the tape.

The important files are probably 2, 5, and 8. These contain 64 records of 16384 bytes each. From experience, the user knows that imagery tends to come in sizes like 512 pixels by 512 lines, or 1024 x 1024 or 2048 x 2048. Since: 

        64 * 16384 = 1048576 = 1024 * 1024,
it is probable that each of files 2, 5, and 8 contain a single channel of imagery with dimensions 1024 pixels by 1024 lines. Each record of 16384 bytes would thus contain 16 lines of the image (16*1024 = 16384). Note: it is quite common to pack more than one line of imagery into a record on tape, since this allows more data to be put on a tape.

@@ifpace To check this assumption, the PACE tape reading programs MIB and MVB can be used. For example, to read the first suspected image file off tape and transfer it to the display: 

 EASI> MTIW = 0,0,1024,1024             | size of image
 EASI> VDOW =                           | overview to display
 EASI> VDOC = 1                         | single channel to display
 EASI> RECL = 16384                     | record length
 EASI> NLPR = 16                        | 16 lines per record
 EASI> SKRC = 0                         | don't skip any records
 EASI> FRAM = 2                         | second file on tape
 EASI> RUN MVB                          | transfer to display
About PCI Help Gateway