The pm's part of the process table is declared in the header file:

pm/mproc.h

Each entry of the table is of type struct mproc and the pm's whole table is an array:

struct mproc mproc[NR_PROCS];

where NR_PROCS is a macro definition for the size of the process table (maximum number of user processes).

The struct mproc entry for a given process contains the process table entries that are managed by the pm.

NR_PROCS is defined in the include file

 /usr/include/minix/config.h

which defines it in terms of _NR_PROCS in

/usr/include/minix/sys_config.h:

config.h:
#include <minix/sys_config.h>
#define NR_PROCS _NR_PROCS

sys_config.h:
#define _NR_PROCS 100