Next: , Previous: Portable File Structure, Up: Portable File Format


A.3 Portable File Header

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. ASCII or 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:

0–60
Control characters. Not important enough to describe in full here.
61–63
Reserved.
64–73
Digits `0' through `9'.
74–99
Capital letters `A' through `Z'.
100–125
Lowercase letters `a' through `z'.
126
Space.
127–130
Symbols .<(+
131
Solid vertical pipe.
132–142
Symbols &[]!$*);^-/
143
Broken vertical pipe.
144–150
Symbols ,%_>?`:
151
British pound symbol.
152–155
Symbols @'=".
156
Less than or equal symbol.
157
Empty box.
158
Plus or minus.
159
Filled box.
160
Degree symbol.
161
Dagger.
162
Symbol `~'.
163
En dash.
164
Lower left corner box draw.
165
Upper left corner box draw.
166
Greater than or equal symbol.
167–176
Superscript `0' through `9'.
177
Lower right corner box draw.
178
Upper right corner box draw.
179
Not equal symbol.
180
Em dash.
181
Superscript `('.
182
Superscript `)'.
183
Horizontal dagger (?).
184–186
Symbols `{}\'.
187
Cents symbol.
188
Centered dot, or bullet.
189–255
Reserved.

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 SPSSPORT in the portable file's character set, which can be used to verify that the file is indeed a portable file.