The COMMON option directs the compiler to generate CM linkage records for EXTERNAL STATIC variables.
.-NOCOMMON-. >>-+-COMMON---+------------------------------------------------><
Under the COMMON option, if the NORENT option applies, then CM linkage records will be generated for EXTERNAL STATIC variables that are not RESERVED and which contain no INITIAL values. This matches what the OS PL/I compiler did.
Under the NOCOMMON option, SD records will be written as was true in earlier releases of Enterprise PL/I.
The COMMON option must not be used with the RENT option or with LIMITS(EXTNAME(n)) if n > 7.