Every portable file begins with a 464-byte header, consisting of a 200-byte collection of vanity splash strings, followed by a 256-byte character set translation table, followed by an 8-byte tag string.
The 200-byte segment is divided into five 40-byte sections, each of
which represents the string
charset SPSS PORT FILE in a
different character set encoding, where charset is the name of
the character set used in the file, e.g.
EBCDIC. Each string is padded on the right with spaces in its
respective character set.
It appears that these strings exist only to inform those who might view the file on a screen, and that they are not parsed by SPSS products. Thus, they can be safely ignored. For those interested, the strings are supposed to be in the following character sets, in the specified order: EBCDIC, 7-bit ASCII, CDC 6-bit ASCII, 6-bit ASCII, Honeywell 6-bit ASCII.
The 256-byte segment describes a mapping from the character set used in the portable file to an arbitrary character set having characters at the following positions:
Control characters. Not important enough to describe in full here.
Digits ‘0’ through ‘9’.
Capital letters ‘A’ through ‘Z’.
Lowercase letters ‘a’ through ‘z’.
Solid vertical pipe.
Broken vertical pipe.
British pound symbol.
Less than or equal symbol.
Plus or minus.
Lower left corner box draw.
Upper left corner box draw.
Greater than or equal symbol.
Superscript ‘0’ through ‘9’.
Lower right corner box draw.
Upper right corner box draw.
Not equal symbol.
Horizontal dagger (?).
Centered dot, or bullet.
Symbols that are not defined in a particular character set are set to the same value as symbol 64; i.e., to ‘0’.
The 8-byte tag string consists of the exact characters
in the portable file’s character set, which can be used to verify that
the file is indeed a portable file.