Rich Alderson <RichA at livingcomputers.org> writes:
  The 5 characters per word is irrelevant to a
discussion of tape, whether
 9- or 7-track:  That's how ASCII text was represented in memory, on disk,
 on DECtape, or on any other word-oriented medium.  Representing the bits
 in an ASCII character by the character itself (to make divisions on the
 tape more clear), this appears diagrammatically as follows:
 Text: HELLOworld
 Memory:
 HHHHHHHEEEEEEELLLLLLLLLLLLLLOOOOOOO_wwwwwwwooooooorrrrrrrlllllllddddddd_
 Core Dump:      High Density:   SIXBIT: (7 track)
 HHHHHHHE        HHHHHHHE        HHHHHH
 EEEEEELL        EEEEEELL        HEEEEE
 LLLLLLLL        LLLLLLLL        EELLLL
 LLLLOOOO        LLLLOOOO        LLLLLL
 ....OOO_        OOO_wwww        LLLLOO
 wwwwwwwo        wwwooooo        OOOOO_
 oooooorr        oorrrrrr        wwwwww
 rrrrrlll        rlllllll        wooooo
 lllldddd        ddddddd_        oorrrr
 ....ddd_                        rrrlll
                                 lllldd
                                 ddddd_ 
Let's add ANSI-ASCII:
.HHHHHHH
.EEEEEEE
.LLLLLLL
.LLLLLLL
_OOOOOOO
.wwwwwww
.ooooooo
.rrrrrrr
.lllllll
_ddddddd
The nice property with this format is that ASCII text in 36-bit words
comes out as ASCII text in octets, while also preserving binary 36-bit
data.