16 Dec
2015
16 Dec
'15
11:11 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chuck
Guzis
Sent: 16 December 2015 18:08
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: Re: IBM CMS dumpfile idiocy
On 12/16/2015 07:57 AM, Paul Koning wrote:
some
IBM standard labels are older than ANSI. Then
again, IBM (in OS/360
at least) had something they called "ANSI label" that were not
actually ANSI at all. They used "8 bit ASCII" which was a bizarre
code created from standard 7 bit ASCII by moving one or two of the
bits (bit 6 to bit 7? I don't remember).
Then there's 6 bit ASCII/USASCII. I was trying to avoid using jargon that
would not understand. I'm quite familiar with IBM
EBCDIC "SL"
tape labels.
My point was that the CMS dumpfile tape isn't even a standard labeled
tape.
It just starts out with the first block of data and
ends with a double
filemark.
No standard labels anywhere. Any non-CMS system would
not know what
the heck the thing was.
--Chuck
That's for the same reason MS DOS does not put standard labels on DDS or DAT
tape. CMS is the original personal computing environment. Each user gets an
individual isolated virtual machine and the IPL's CMS into their machine.
CMS is a single-user operating system and within that virtual machine they
can do what they want. A normal user can't see much outside their virtual
environment, but inside it they are god. They can even single step through
CMS. As there are many VMs in a VM/370 environment Users can put whatever
they want on their tapes. It is up to the operators or other privileged user
to "attach" the physical tapes to the users' virtual machine and mount the
tapes with or without a ring. Once its attached the user can put what they
want on the tape, provided it has a write ring in it. Trying to insist on
standard labels would be pretty pointless.
CMS TAPE files are not intended to be used by other systems and the format
is undocumented (well except a little in the source code) and has changed
several times as disk formats have changed. They contain physical dumps of
the DASD (disk) followed by the matching directory block. They may contain
multiple files. You know a file is complete when you hit is directory block.
So unlike OS tapes you don't need to specify a block factor and record type.
You just do "TAPE DUMP <filename> <filemode> <disk letter> where
the names
may contain the usual wild cards and they get dumped. To see what is on a
tape do "TAPE SCAN" and to load them do "TAPE LOAD". No JCL, no DD
cards no
knowledge of the underlying record formats are required.
CMS includes a "MOVEFILE" command that can produce standard label tapes in
the usual OS/DOS formats but normally users don't bother unless they are
sending tapes to other sites...
Dave