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53 lines
2.1 KiB
Plaintext
Executable File
53 lines
2.1 KiB
Plaintext
Executable File
-*- Text -*- This is the file AI:SYSDOC;DUMP FORMAT
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Copyright (c) 1999 Massachusetts Institute of Technology
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See the COPYING file at the top-level directory of this project.
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------------------------------
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This file attempts to document the format of DUMP tapes.
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It probably contains inaccuracies.
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Each tape record contains 1,024 36-bit words in "core dump" format;
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thus on 7-track tape each 36-bit word takes 6 tape frames. Data
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formats are standard pdp-10 data formats such as sixbit (6 characters
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per word), 7-bit ascii (5 characters per word, left-justified),
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halfwords, and so forth.
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Each file dumped to tape consists of a header, then the 36-bit data of
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the file, and ends with an end-of-file mark. The last record in a file
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will generally be shorter than 1,024 words, depending on the length
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of the file. There is no padding, other than the usual control-C's
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padding a text file out to a word boundary. The tape ends with a
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double end-of-file mark.
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The first file on the tape is preceded by a tape header in front
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of the file header, with no end-of-file mark in between.
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Each type of header starts with a 36-bit word whose left half is minus
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the number of words in the header, including this word. The right
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half of this word is zero.
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Tape header:
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-LTHBLK,,0
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tape number,,reel number
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tape creation date in sixbit
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type of tape (0 random, >0 full dump, <0 incremental dump)
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File header:
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-LHBLK,,0
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directory name in sixbit
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first file name in sixbit
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second file name in sixbit
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disk pack number where file was
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creation date of file (same format as in ITS directory)
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If the file is really a link, then the left half of the
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pack number is non-zero and the data of the file consists of
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three words, containing the sixbit file name the link points to.
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In addition to files, directories also appear on some dump tapes. The
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master file directory has name M.F.D. (FILE) and a user file directory
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has name .FILE. (DIR). The data for the master directory is an exact
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binary copy of the directory as stored on disk. The data for a user
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directory is almost an exact binary copy except that unused space
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between the descriptor area and the name area is squished out. |