When we talk about free software, we usually refer to the free software licenses. We also need relief from software patents, so our freedom is not restricted by them. But there is a third type of freedom we need, and that's user freedom. Expert users don't take a system as it is. They like to change the configuration, and they want to run the software that works best for them. That includes window managers as well as your favourite text editor. But even on a GNU/Linux system consisting only of free software, you can not easily use the filesystem format, network protocol or binary format you want without special privileges. In traditional Unix systems, user freedom is severly restricted by the system administrator.

The Hurd is built on top of CMU's Mach 3.0 kernel and uses Mach's virtual memory management and message-passing facilities. The GNU C Library will provide the Unix system call interface, and will call the Hurd for needed services it can't provide itself. The design and implementation of the Hurd is being lead by Michael Bushnell, with assistance from Richard Stallman, Roland McGrath, Jan Brittenson, and others.

A MORE USABLE APPROACH TO OS DESIGN

The fundamental purpose of an operating system (OS) is to enable a variety of programs to share a single computer efficiently and productively. This demands memory protection, preemptively scheduled timesharing, coordinated access to I/O peripherals, and other services. In addition, an OS can allow several users to share a computer. In this case, efficiency demands services that protect users from harming each other, enable them to share without prior arrangement, and mediate access to physical devices.

On today's computer systems, programmers usually implement these goals through a large program called the kernel. Since this program must be accessible to all user programs, it is the natural place to add functionality to the system. Since the only model for process interaction is that of specific, individual services provided by the kernel, no one creates other places to add functionality. As time goes by, more and more is added to the kernel.