To estimate the amount of free work disk space required for a PROC SORT,
use the following formula:

   free_bytes_required=(key_variable_length + observation_length) *
   number_of_observations * 4

Where you know the following:

   key_variable_length:  Length of sorting variable.
      Example: If you are sorting by a character variable with a length
               of 10, this would produce a key_variable_length of
               10 bytes. A numeric variable would be 8 bytes.

   observation_length: Total number of bytes in an observation.
      Add together the bytes for all variables in one observation.

   number_of_observations: Total number of observations in a data set.

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