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In SAS 6 of the SAS System, the position of variables on a SAS data
set is determined by the order in which they are encountered regardless
of their type or length. In order to improve performance, SAS 7 and
beyond of the SAS System positions 8 byte and 4 byte numeric variables
at 8 byte boundaries at the front of a SAS data set. Note that if the
data set has 4 byte numerics but not 8 byte numerics, alignment is based
on 4 byte boundaries instead. Character variables are placed next in the
order in which they are encountered, followed by all other numeric
variables in the order in which they were encountered. The position of
the variable can be viewed in PROC CONTENTS output in the POS column or
the NPOS variable when an output data set is created via the OUT=
option.

Although the physical position of variables on the data set may be
different, the logical order of variables has not changed. The logical
order of variables can be viewed in PROC CONTENTS output in the '#'
column or the VARNUM variable when an output data set is created via the
OUT= option.

Additionally, the 'Observation Length' reported by PROC CONTENTS in
SAS 7 and beyond may be larger than the same data set created by
SAS 6. This occurs because each observation is padded so that the
subsequent observation aligns at the beginning of either an 8 byte or 4
byte boundary (if no 8 byte numeric variables exist) in the newer
releases.

For example, consider the following code and partial output it produces
in SAS 6.

   data one;
     length x 6 y 4;
     s=3;
     a='a';
     x=1;
     y=5;
   run;
   proc contents;
   run;

   -----Alphabetic List of Variables and Attributes-----

        #    Variable    Type    Len    Pos
        -----------------------------------
        4    A           Char      1     18
        3    S           Num       8     10
        1    X           Num       6      0
        2    Y           Num       4      6

Additionally, the observation length is reported as 19 bytes. Below is
the comparable output from SAS 8, which reports the observation
length as 24 bytes.



   -----Alphabetic List of Variables and Attributes-----

        #    Variable    Type    Len    Pos
        -----------------------------------
        4    a           Char      1     12
        3    s           Num       8      0
        1    x           Num       6     13
        2    y           Num       4      8


Due to the change in the algorithm determining physical position, the
POSITION option on PROC CONTENTS has been replaced by the more
descriptive VARNUM option. The POSITION option still produces output
ordered by the logical position of variables on the data set, but it is
no longer documented. In SAS 9, the POSITION option is still accepted
syntax, but no Pos field is in the printed output. If you use the OUT=
option on PROC CONTENTS, the NPOS variable is written to the data set.

Operating System and Release Information