ansitape(4) CLIX ansitape(4)
NAME
ansitape - ANSI standard magtape label
DESCRIPTION
An ANSI-labeled tape starts with a volume header. This header specifies
the volume name and protection, the owner of the volume, and the ANSI
label standard level to which the tape conforms.
Every file on the tape has a header, data blocks, and a trailer. A tape
mark follows each element. At the end of the tape, two tape marks follow
the trailer to indicate logical end-of-tape.
If a file is too large to be copied on one tape, it may be continued on
another tape by modifying the trailer section.
VOLUME HEADER
Field Width Example Use
________________________________________________
VOL1 4 VOL1 Indicates this is a
volume header.
Label 6 VAX1 The name of the
volume.
Access 1 <space> Volume protection.
<space> means
unprotected.
IGN1 20 << ignored >>
IGN2 6 << ignored >>
Owner 14 Joe User The name of the
user.
IGN3 28 << ignored >>
Level 1 3 ANSI standard level.
________________________________________________
Owner The owner field is 14 characters in ANSI labels. IBM labels cut
the owner field to 10 characters. The IGN2 field is 10 characters
on IBM-format tapes.
FILE HEADER 1
Field Width Example Use
________________________________________________
HDR1 4 HDR1 Identifies
first file
header.
Name 17 FILE.DAT Leftmost 17
characters of
filename.
Set Name 6 VAX1 Name of volume
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set this file
is part of.
Vol Num 4 0001 Number of this
volume within
volume set.
File Num 4 0001 Number of file
on this tape.
Generation 4 0001 Resembles a
major release
number.
Gen Version 2 00 Version of a
file within a
release.
Created 6 b86001 The date of
file creation.
Expires 6 b86365 Date file
expires.
Access 1 <space> File
protection.
<space> means
unprotected.
Blockcount 6 000000 Number of
blocks in the
file.
System 13 OS360 The name of the
software system
that created
the tape.
IGN 7 << ignored >>
________________________________________________
Name The filename may have up to 17 characters in IBM labels, and
ANSI labels before standard level 3. On ANSI level 3 and
after, the HDR4 record provides overflow storage for up to 63
more characters of the filename.
Set Name On multireel tape sets, a name identifying the set as a
whole. Normally, this is just the volume name of the first
reel in the set.
Generation Resembles a major release number. The version field is a
version within a generation. On VAX/VMS systems, these two
fields are mathematically related to the (single) version
number of disk files.
Created The date the file was created. This is a six-character
field; the first character is always a space. The next two
are the year. The final three are the day within the year,
counting January 1st as day 1.
Blocks The number of blocks in the file. In HDR1 records, this is
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always 0. The corresponding EOF1 or EOV1 contains the number
of tape blocks written in the file on the current reel.
FILE HEADER 2
Field Width Example Use
_____________________________________________________________
HDR2 4 HDR2 Second file header.
Rec Format 1 D Record format.
Blk Length 5 02048 Tape block size.
Rec Length 5 00080 Record size.
Density 1 3 Recording density code.
Vol Switch 1 0 1 if this is a
continuation of a file
from a previous reel.
Job 17 user/program See following notes.
Recording 2 <space> Unused in 9-track tapes.
Car Control 1 <space> See following notes.
Blocking 1 B See following notes.
IGN 11 << ignored >>
Offset 2 00 Bytes to skip at front
of each block.
_____________________________________________________________
Rec Format
A single character indicating what type of records are provided.
The codes are as follows:
Code Meaning
________________________________
F Fixed-length
D Variable up to rec length
V IBM code for variable
U Unknown
________________________________
Job The name of the job (username in CLIX) right-padded to eight
characters, a slash (/), and the job step (program name in CLIX)
right-padded to eight characters. This identifies where the JCL
was located when this file was created.
Carriage Control
Normally a space, indicating that the records do not contain
carriage control information. When displayed, each record is
placed on a separate line. If an ``A'' is used, the first
character of each record is presumed to be a FORTRAN carriage-
control character. VAX/VMS also uses ``M'' to indicate that
carriage-control is embedded as part of the data. This is usually
used in the case of binary files.
Blocking
The B indicates that the number of records that will fit are placed
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in a physical tape block. Records do not cross block boundaries.
A space indicates only one record per physical tape block.
The HDR3 and HDR4 labels are not written on IBM tapes. ANSI allows but
does not require these labels.
FILE HEADER 3
Field Width Example Use
_____________________________________________________
HDR3 4 HDR3 Third file header.
OS 76 Operating-system dependent.
_____________________________________________________
OS This field is reserved for the operating system that created the file
to use. Other operating systems should disregard HDR3 records. On
VAX/VMS, this record contains the RMS file description.
FILE HEADER 4
Field Width Example Use
________________________________________________________
HDR4 4 HDR4 Fourth file header.
Name 2 63 Name continuation from HDR1.
Unknown 2 00 Unknown, fill with 00.
IGN 11 << ignored >>
________________________________________________________
Name 2 On ANSI tapes, if the filename is longer than 17 characters, the
first 17 are placed in the HDR1 record. The next 63 are put in
HDR4. Filenames longer than 80 characters are truncated. A HDR3
record is not required in order to have a HDR4.
File Trailing Labels
These labels are written after a tape file. Every label written at the
head of the file will have a corresponding label at the tail. Except for
the blockcount field in HDR1, the only difference is in the name of the
label. If we have reached the logical end of the file, the characters HDR
in the headers are replaced by the characters EOF in the trailing labels.
If we are not at the logical end of the file, but are merely pausing at
the physical end-of-tape before continuing on another reel, the HDR
characters are replaced by EOV (end-of-volume).
The blockcount field of HDR1 was initially recorded as 000000. When the
trailers are written, the block count is changed to indicate the number of
tape data blocks written. A file continued over several volumes maintains
separate counts for each reel.
Record Formats
The two basic record formats are fixed and variable.
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Fixed format uses records that all have a constant length. This is true
with VAX/VMS executable images (record length = 512). It is also used by
IBM systems for text files, with a record length of 80 (card images). The
record size field of HDR2 tells the length of each record.
With fixed-length records, the block-size is usually selected to be some
multiple of the record-size. The number of records that will fit is
placed in each block. Since records do not (normally) span physical tape
blocks, extra space at the end of a block is wasted.
Variable-length records are used by VAX/VMS for text files. The CLIX
command ansitape(1) also turns CLIX text files into variable-length tape
files. With this format, the record length specified in HDR2 is an upper
limit.
Each record is proceeded by a four digit (zero-filled) byte count. The
count included the digits themselves, so the minimum valid number is 0004.
These four digits specify the length of the record. The data follows the
digits, and is, in turn, followed by the digits for the next record.
When writing, ansitape(1) checks to ensure enough room is in the tape
block for the next record. If the record (including its length digits)
will not fit, the current block is sent to the tape and a new block is
started. Unused space at the end of the tape block is filled with
circumflex (^) characters.
RELATED INFORMATION
Commands: ansitape(1)
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