[Simh] PDP-10 DECtapes

Thu Mar 28 15:19:41 EDT 2013

On 2013-03-28 19:23, Timothe Litt wrote:
> Good information, but this thread is about DECtape, not 9-Track magtapes...

Right.

> The format looks about right for 9-track DOS-11 magtapes; I remember
> writing code to extract files from them on the -10.
>
> It's not right (or at least, not complete) for the block-addressable
> DECtapes.

DECtapes (atleast on RSX) are Files-11 ODS-1 volumes, and not ANSI 
labelled tapes. They have nothing in common with each other, apart from 
both being tapes. The closest relative to a DECtape is a floppy.

Also, the DOS-11 tape format is not the same as ANSI labelled tapes. 
They are not compatible.

In RSX, ANSI labelled tapes are accessed through MTAACP, and the tapes 
are mounted as a known format. You then access them with the normal 
tools you'd use for any normal work in RSX. (Such as PIP.)
DOS-11 tapes are instead mounted foreign, and you need FLX to read/write 
to them.

	Johnny

> I don't think DOS-11 would have been documented in any of the references
> cited.
>
> There's now a SIMH repo on github; your utility could go into the tools
> section.
>
> This communication may not represent my employer's views,
> if any, on the matters discussed.
>
> On 28-Mar-13 14:09, Larry Baker wrote:
>> On 28 Mar 2013, at 5:24 AM, <simh-request at trailing-edge.com
>> <mailto:simh-request at trailing-edge.com>>
>> <simh-request at trailing-edge.com
>> <mailto: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 <mailto:baker at usgs.gov>
>>
>>
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>
>
>
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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol