IBM compatible tape structure (*1) consists of a series of label blocks describing the volume and each file (Data Set). Essential the structure looks like this:

  • VOL1..9 Volume header
    • VOL1 Naming the Volume and optional owner (*2)
  • HDR1..9 File header
    • HDR1 Basically the directory entry for the file following
    • HDR2 Description of the internal file structure like block length or record length
  • Data Blocks
  • EOF1..9 End of file markers
    • EOF1/2 Basically a repetition of the HDR1/2 blocks
  • [more files if present, covered by HDRx/EOFx blocks]
  • EOV1/2 End of Volume markers in case of files spreading over multiple tapes

This structure is at least present since TOS/360 of 1964 and as well defined in a later ANSI standard (*3).


Has this structure been used before 1964 and which system or software did so?

(I'm prety sure it was, but I can't find any reference among my old manuals)

*1 - Essential disk structure as well.

*2 - Much like the Volume name entry of a MS-DOS 1.28 root directoy.

*3 - With some extensions like allowing larger block length than 80 bytes for labels.

  • 4
    This 1963 document describes a different "IBM standard label" - BCD encoded. The standard you quote is focused on 9-track tapes with provision for 7-track tapes, but the two 7-track formats are not the same. E.g., the older headers have "1HDR" identifiers and the later standard has "HDR1". Most likely the newer standard came in at the same time as EBCDIC and 9-track tapes, i.e., with S/360. Feb 12 '20 at 2:41
  • 1
    From what I've noticed and seen over the years, the described tape label format was introduced with System/360 operating systems (OS/360, DOS/360, TOS/360). TOS/360 and DOS/360 were the same operating system; one was designed for systems that only had tape drives, as well as unit record equipment. DOS/360 had tape support; eventually the need for a tape-only operating system disappeared. Feb 14 '20 at 0:59

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