the compilation phase

At compile time, SAS creates
1. an input buffer to hold the current raw data file record that is being processed
2. a program data vector (PDV) to hold the current SAS observation
3. the descriptor portion of the output data set.

The PDV contains two automatic variables that can be used for processing but which are not written to the data set as part of an observation:
_N_ counts the number of times that the DATA step begins to execute
_ERROR_ signals the occurrence of an error that is caused by the data during
execution.
0 is the default which means there is no error.
1 there is one or more errors.

During the compilation phase, SAS also scans each statement in the DATA step, looking for syntax errors. Syntax errors include:
1. Missing or misspelled keywords
2. Invalid variable names
3. Missing or invalid punctuation
4. Invalid options

Summary of the compilation phase
1. During the compilation phase, the input buffer is created to hold a record from the external file.
2. The PDV is created to hold the current observation
3. The descriptor portion of the SAS data set is created.