Kernels always have some code built in to gather statistics. In the case of cpus, several times a second a clock routine fires off and increments one element of a structure. The structure will have counters for idle, user, system, and so on.

In the old days, you could get the structure if you knew its name. You would run nlist(3) on the kernel's symbol table to get the address of the structure. Then you opened /dev/kmem. did a seek to the address and read the structure. The c definations of the structures were usually in /usr/include. This still can be made to work on hp-ux, but the required information is no longer supplied in /usr/include. Skilled gurus can reverse-engineer it, but it's difficult. Vic Able has done this to get lsof to work on recent versions of HP-UX, a feat that very few could match.

New system calls like pstat are the way of the future. And pstat works well enough. Why do you want an alternative?