[Simh] PDP-10 DECtapes

[Larry Baker]

On 28 Mar 2013, at 5:24 AM, <simh-request at trailing-edge.com> <simh-request at trailing-edge.com> wrote:

> Google 'AA-JS16A-TC' for some Files-11 format information; I'd 
> have to think a bit on the DOS-11 format.


RSX/VMS Files-11 tapes are ANSI labeled tapes.  I know OpenVMS also used HDR3/4 labels for RMS information.  There was a MOUNT option to suppress writing those labels.

I wrote an RSX/VMS  program that will scan an unknown tape and decode it for you.  (If anyone wants it, let me know where I should upload it.)  The DOS format decoder looks for a 14 byte (physical) record at the start of the file.  It is decoded by the following code:

C
C...  DEC DOS labels
C
      Call R50ASC ( 6, buffer( 1), ascbuf( 1) )
      Call R50ASC ( 3, buffer(13), ascbuf( 7) )
      ascbuf(10) = '.'
      Call R50ASC ( 3, buffer( 5), ascbuf(11) )
      ltemp(1) = buffer(7)
      ltemp(2) = 0
      mem = itemp
      ltemp(1) = buffer(8)
      grp = itemp
      ltemp(1) = buffer(11)
      ltemp(2) = buffer(12)
      jday = MOD(itemp,1000)
      year = itemp/1000 + 70
      Call JDCONV ( jday, mon, day, year )
      ltemp(1) = buffer( 9)
      ltemp(2) = buffer(10)
      Write (STDOUT,619) ifile, grp, mem, ascbuf, day, month(mon),
     1                   year, itemp
  619 Format (//' File ', I4, ':', T34, '"', '[', O3.3, ',', O3.3, ']',
     1        13A1, 2X, I2, '-', A, '-', I2.2, '  <', O3.3, '>', '"')

The DOS label contents are:

Words 1-2 RAD50 characters 1-6 of the file name part (before the implied period)
Word 3 RAD50 characters 1-3 of the file type (after the implied period)
Word 4 Octal File owner's User Identification Code (group code in high-order byte, member code in low-order byte)
Word 5 Binary File creation date ( 1000 * ( year - 1970 ) + Julian day )
Word 6 Octal File protection (low-order to high-order RWED bits: read, write, extend, delete; grouped low-order to high-order for system, owner, group, world)
Word 7 RAD50 characters 7-9 of the file name part (before the implied period)

The references I used to write the program (back in the 1980's) are below.  Which reference had the DOS label format I don't remember (if any of them did).

6  References

[1]  American National Standards Institute, 1978, Magnetic Tape Labels
     and File Structure for Information Interchange (ANSI X3.27-1978).

[2]  Digital Equipment  Corp.,  1985,  RSX-11M/M-Plus  MCR  Operations
     Manual (Order no. AA-FD10A-TC).

[3]  Digital Equipment  Corp.,  1985,  RSX-11M-Plus  Command  Language
     Manual (Order no. AA-FD04A-TC).

[4]  Digital Equipment Corp., 1985, RSX-11M/M-Plus and  Micro/RSX  I/O
     Operations Reference Manual (Order no. AA-FD14A-TC).

[5]  Digital  Equipment  Corp.,  1985,  RSX-11M/M-Plus   I/O   Drivers
     Reference Manual (Order no. AA-FD09A-TC).

[6]  Digital Equipment Corp., 1984, VAX/VMS Command Definition Utility
     Reference Manual (Order no. AA-Z408A-TE).

[7]  Digital Equipment Corp., 1986, VAX/VMS DCL Dictionary (Order  no.
     AA-Z200C-TE).

[8]  Digital Equipment Corp., 1984, VAX/VMS  Mount  Utility  Reference
     Manual (Order no. AA-Z424C-TE).

[9]  Digital Equipment Corp., 1986, Guide to VAX/VMS Disk and Magnetic
     Tape Operations (Order no. AI-Y506B-TE).

[10] Digital Equipment  Corp.,  1986,  VAX/VMS  I/O  User's  Reference
     Manual:  Part I (Order no. AA-Z600C-TE).

[11] International Business Machines Corp., 1978,  OS/VS  Tape  Labels
     (Order No. GC26-3795-1).

Larry Baker
US Geological Survey
650-329-5608
baker at usgs.gov
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