There are several global Minix kernel variables related to scheduling processes:

/* Process scheduling information and the kernel reentry count. */
EXTERN struct proc *prev_ptr;   /* previously running process */
EXTERN struct proc *proc_ptr;   /* pointer to currently running process */
EXTERN struct proc *next_ptr;   /* next process to run after restart() */
EXTERN struct proc *bill_ptr;   /* process to bill for clock ticks */