Mach number a small area around the object's leading edge. (Fig.1b) Fig. 1. "Mach number in transonic airflow around an airfoil; M < 1 (a) and M > 1 (b)." When an aircraft exceeds Mach 1 (i.e. the sound barrier), a large pressure difference is created just in front of the aircraft. This abrupt pressure difference, called a shock wave, spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone). It is this shock wave that causes the sonic boom heard as a fast moving aircraft travels overhead. A person inside the aircraft will not hear this.
GNU Mach by Thomas Bushnell (rather than by a Utah researcher) is from 16 December 1996. In 2002, Roland McGrath branched the OSKit-Mach branch from GNU Mach 1.2, intending to replace all the device drivers and some of the hardware support with code from OSKit. After the release of GNU Mach 1.3, this branch was intended to become the GNU Mach 2.0 main line; however, as of 2006, OSKit-Mach is not being developed. GNU Mach 1.4 was released on 27 September 2013, eleven years after 1.3. GNU Mach GNU Mach is an implementation of the Mach microkernel. It is the default microkernel