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.
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.