Difference between Linux and Hurd, from an (advanced) user/programmer point-of-view

Question

I've seen that systems running on top of Hurd start to become available (namely Arch Hurd) and I was wondering how a user, anyhow advance s/he can be, can see a difference?

Linux and BSD should be pretty much the same, because both of them are monolithic kernel, so the only difference should be their syscall API.

NB: when I write Linux, I don't mean GNU/Linux, as I guess that the GNU environment should eventually be the same in both systems

EDIT: deleted the statement about BSD, I don't know anything about this system and that's not the point of my question :$

EDIT 2: Let's try another approach: I have a good knowledge of GNU/Linux. What would be different with GNU/Hurd? for instance,

• module certainly can't exist with a micro-kernel, what's the equivalent? how does a video card driver looks like ?
• if the Hurd kernel (Mach) delegates core-tasks to user-space processes, which are they?
• who is in charge of these core tasks ? (an equivalent of super-init?)

(side-question: does this question belongs to stackoverflow?)

Answer 1

Hurd -> Microkernel

while

Linux -> Monolithic kernel

similar to the difference b/w monolithic kernel and Microkernel

1 ) Monolithic kernel is much older than Microkernel. It’s used in Unix . While Idea of microkernel appeared at the end of the 1980's.

2 ) the example of os having the Monolithic kernels are UNIX , LINUX While the os having Microkernel are QNX , L4 , HURD , initially Mach (not mac os x) later it will converted into hybrid kernel , even MINIX is not pure kernel because device driver are compiled as part of the kernel .

3 ) Monolithic kernel are faster than microkernel . While The first microkernel Mach is 50% slower than Monolithic kernel while later version like L4 only 2% or 4% slower than the Monolithic kernel .

4 ) Monolithic kernel generally are bulky . While Pure monolithic kernel has to be small in size even fit in s into processor first level cache (first generation microkernel).

5) in the Monolithic kernel device driver reside in the kernel space . While In the Microkernel device driver reside in the user space.

6 ) since the device driver reside in the kernel space it make monolithic kernel less secure than microkernel . (Failure in the driver may lead to crash) While Microkernels are more secure than the monolithic kernel hence used in some military devices.

7 ) Monolithic kernels use signals and sockets to ensure IPC while microkernel approach uses message queues . 1 gen of microkernel poorly implemented IPC so were slow on context switches.

8 ) adding new feature to a monolithic system means recompiling the whole kernel While You can add new feature or patches without recompiling.

Answer 2

Why not first read up on what HURD is: http://www.gnu.org/software/hurd/hurd/what_is_the_gnu_hurd.html

In short (from my understanding) HURD is a kernel running on top of a MACH micro kernel allowing for updates of even the HURD kernel stuff without a reboot.

That is all nice and theoretic, but in practice the only thing you'll notice is the lack of (driver) support for HURD.

HURD is like BSD and LINUX . . all pretty much the same but different. They are all kernels with their own pros and cons.