This is a part of collection of HP-UX tips from the time I worked as system admin:
The information below is the result of my researches in the Internet and of my experiences. It is solely used for my purpose and may not be suitable for others.
First off, in all versions of HP-UX prior to 11.00, the kernel is always 32-bit. That being said, on 11.x systems, there are several ways to determine whether you're running a 32 or 64 bit kernel...
From the command-line
$ getconf KERNEL_BITS
$ file /stand/vmunix
/stand/vmunix: PA-RISC1.1 executable ---> 32-bit
/stand/vmunix: ELF-64 executable object file ---> 64-bit
1) goto Performance Monitors -> System Properties -> Operating System
2) check OS Kernel Width: value