Unix servers from Hewlett Packard use proprietary firmware to enable them to boot up to an operating system. For those not used to it, this firmware can seem a little strange and cryptic. This document will familiarize you with this firmware and explain the HP boot sequence.

This document explains the boot sequence of a "stock" HP server, that is, a server that is running HP's proprietary Unix operating system, HP-UX. If you are running linux on an HP, you will have another boot loader such as palo. Regardless of the flavor of Unix you are running, the firmware and boot sequence are similar. The examples that I use are from a HP rp5450 L2000 "L Class" server, but I regularly use A, D, R, K and L class servers, and in my experience the PDC on all of those platforms are almost identical.

When a HP boots it runs some diagnostic routines and (eventually) comes to a firmware prompt. This firmware serves as the intermediary between the processor and hardware and the operating system. HP calls it the Processor Dependent Code - PDC. It varies from model to model of HP server, depending on hardware configuration, but it generally looks very similar regardless of model. The PDC is relatively equivalent to BIOS on an Intel based system.

In a "stock" HP, the next step in the boot sequence is to load an Initial System Loader (ISL) utility from the boot medium, usually disk. Note that HP uses the term Initial Program Loader (IPL) interchangeably with ISL.

The final step before boot is that ISL loads an operating system loading utility named HPUX from disk or other boot medium. The HPUX utility then loads the kernel, usually /stand/vmunix in a "stock" HP running HP-UX.