The descriptor portion of an uncompressed data file is always stored at the end of the first data set page. New observations are always added to the end of the data set, and deleted observation space is neither tracked nor reused.

The descriptor portion of a compressed data file is always stored at the end of the first data set page. If you specify REUSE=YES, SAS tracks and reuses deleted observation space within a compressed data file. Therefore, every observation in a compressed data file can be a different size. Compressed data files do have a larger overhead than uncompressed data files.

Use the LENGTH statement to assign a reduced length to a numeric variable. If you do not use the LENGTH statement to define a reduced length for numeric variables, their default length is 8 bytes. The FORMAT statement associates a format with a variable, and the INFORMAT statement associates an informat with a variable.

SAS data views use significantly less disk space than SAS data files. However, SAS data views might need more CPU resources than SAS data files. You can create a SAS data view in either the temporary SAS library or in a permanent SAS library.

Use the COMPARE procedure to detect any differences in the values of two data sets. The COMPARE statement is not valid syntax in either the CONTENTS procedure or the DATASETS procedure. Printing both data sets might not reveal differences in the precise values of the shortened variables, depending on the formats that are used.