The /Zi option produces an object file containing line numbers and full symbolic-debugging information for use with the CodeView window-oriented debugger. This symbolic information is a map of your source code that the debugger uses. It includes such things as variable names and their types, function names and their return types, and the number and names of all of the program's segments. The object file also includes full symbol-table information and line numbers.
The /Zd option produces an object file containing only global and external symbol information and line number information. Use this option when you want to reduce the size of an executable file that you will be debugging with the CodeView debugger. You can also use /Zd when you do not need to use the expression evaluator during debugging.
Example
CL /c /Zi TEST.C
This command produces an object file named TEST.OBJ that contains line numbers corresponding to the lines in TEST.C.