how does "hpcboot.exe" work?

[DiTBho Down in The Bunny hole <downinthebunnyhole%gmail.com@localhost>]

Hi
I'm studying Windows CE v1, with the goal of trying to modify the IBM
z50 ROM to boot NetBSD (or Linux) directly.

Currently NetBSD is loaded and started via "hpcboot.exe", an
executable that runs on top of Windows CE, loads the kernel into RAM
and starts it.

It's not clear how this works, I mean, doesn't Windows CE restrict RAM
access to an .exe file?

I can't find the source code and documentation for "hpcboot.exe".

Let me know
Thanks.