Knowing both are micro-kernels, what is the difference b/w Mach (on which Hurd is based on) and Minix. Are there any architectural differences? A little light over "what is L4" would be very helpful. I cannot find any documents covering this.
GNU Mach is an implementation of the Mach microkernel. It is the default microkernel in the GNU Hurd operating system.
MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes.
I think that your question is incorrect. What the difference between Linux and FreeBSD? Each of this operating system implemented own system calls, application interfaces, etc.
L4 is a family of second-generation microkernels, generally used to implement Unix-like operating systems, but also used in a variety of other systems. L4, like its predecessor L3 was created by German computer scientist Jochen Liedtke as a response to the poor performance of earlier microkernel-based operating systems.
Read some links bellow: