What is Mach: Definition and 78 Discussions

Mach () is a kernel developed at Carnegie Mellon University by Richard Rashid and Avie Tevanian to support operating system research, primarily distributed and parallel computing. Mach is often mentioned as one of the earliest examples of a microkernel. However, not all versions of Mach are microkernels. Mach's derivatives are the basis of the operating system kernel in GNU Hurd and of Apple's XNU kernel used in macOS, iOS, iPadOS, tvOS, and watchOS.
The project at Carnegie Mellon ran from 1985 to 1994, ending with Mach 3.0, which is a true microkernel. Mach was developed as a replacement for the kernel in the BSD version of Unix, so no new operating system would have to be designed around it. Mach and its derivatives exist within a number of commercial operating systems. These include all using the XNU operating system kernel which incorporates an earlier non-microkernel Mach as a major component. The Mach virtual memory management system was also adopted in 4.4BSD by the BSD developers at CSRG, and appears in modern BSD-derived Unix systems, such as FreeBSD.
Mach is the logical successor to Carnegie Mellon's Accent kernel. The lead developer on the Mach project, Richard Rashid, has been working at Microsoft since 1991; he founded the Microsoft Research division. Another of the original Mach developers, Avie Tevanian, was formerly head of software at NeXT, then Chief Software Technology Officer at Apple Inc. until March 2006.

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  1. R

    Aerodynamics Monographs: Recent Advances in High Mach Subsonic Flight

    Summary:: I'm looking for recommendations of recent aerodynamics monographs which treat high Mach number subsonic (pre-transsonic) flight thoroughly. I'm looking for recommendations of recent aerodynamics monographs which treat high Mach number subsonic (pre-transsonic) flight thoroughly. I...
  2. Vin B

    Simulate mach reflection with mach stem generation using Ansys Fluent

    I need to simulate mach reflection with mach stem generation using on Ansys Fluent. The wedge angle is of 22deg at Mach 5.
  3. theudster

    How to derive the reflected Mach number relationship?

    Hi, when learnig about reflected waves, I keep coming up with this equation; to calculate the reflected mach number (Mr). I can't seem to find the derivation for this and would appreciate your help Thank you
  4. PainterGuy

    Pressure felt by a piston, Mach number of speaker making the sound

    Hi, Once someone wrote the following to me in response to my query. My query was somewhat unrelated to it and I don't even have the copy of query anymore. The pressure felt by the piston at any time is the average component of momentum of a gas molecule that is normal to the piston times the...
  5. D

    What is the relationship between Mach number and compressibility in fluids?

    Homework Statement Hi, The below website states the definition of Mach number, which is a quantity that expresses how compressible a fluid is. https://physics.info/turbulence/ M = sqrt [ ( inertial resistance in the fluid ) / ( compressional resistance in the fluid ) ] = v / c...
  6. T

    I What is the difference between Mach cone and shock wave in aerodynamics?

    Is mach cone the area of the shock wave or the wave front of the Mach wave? Usually the diagram for mach cone is this, However I still see some author states that the Mach cone is the shock wave. Shouldn't the shock wave be at the intersection(between the circles) and if the Mach cone is about...
  7. T

    At supersonic speed, why does Mach number decrease?

    At supersonic speed, air become compressible. However why does Mach number decrease when flow area decrease? I understand that pressure will increase because the density will increase when flow area decrease. However shouldn't the Mach number increase in order to conserve mass flow? Unless the...
  8. R

    Multiphase flow with high Mach number

    Hello everyone I am currently working on multiphase flow in pipe. Will you guys suggest any reference for multiphase flow in pipe with high Mach number (Experiment and Simulation)? Thanks in Advance.
  9. F

    Frame of reference (non inertial/inertial) in an Atwood Mach

    Homework Statement Find the acceleration of blocks 1 and 2 in both a non-inertial frame of reference (an observer accelerating with the machine) and an inertial frame of reference (observer at earth) Homework Equations F = ma The Attempt at a SolutionI solved the question successfully...
  10. J

    Would a reverse wing sweep be better for speeds above Mach 2

    I am curious about a reverse wing sweep because it could be used on an aircraft for turning at high speeds at higher than Mach two.
  11. D

    I Why is there a sonic boom at Mach 1.5?

    It's my understanding that a sonic boom is the doppler effect taken to the extreme, with a sound emitting object traveling at the speed of sound, your building the ultimate constructive wave. I want to know, if you were traveling at Mach 1.5, why doesn't the sound you're generating cancel...
  12. grandpa2390

    What do the sound waves look like after Mach 1?

    I get from pictures that the waves in front of the craft get closer and closer together until at Mach 1 they are on top of each other and boom! but! after that, the sound waves form a cone... what is that? is that the head of each wave being produced behind the previous wave and then blasting...
  13. MaxKang

    Reynolds number & Mach number for flow regime

    "An adverse pressure gradient strongly favors transition to turbulent flow. In contrast, strong favorable pressure gradients (where p decreases in the downstream direction) tend to preserve initially laminar flow." "High values of M∞ and low values of Re tend to encourage laminar flow" Looking at...
  14. G

    Solving Long Mach Nozzle Shape Problem for MBMS

    Hi y'all, thanks in advance to anyone who knows a bit more about compressible/isentropic flow than me for the help, I have an interesting problem which I've been working on for a bit. Basically, I would like to measure species coming out of a reactor using molecular beam mass spectrometry...
  15. C

    B How can we tell that "fictitious forces" are not real?

    Earlier today I was reading through this entire thread: https://www.physicsforums.com/threads/implications-of-the-statement-acceleration-is-not-relative.670653/ And I remained confused about one thing in particular. The original poster made a statement (bolded below) on page 1 that seemed...
  16. T

    Heat-shield for a Mach 30 missile at 10km for 10 seconds?

    Using an ablative carbon-carbon heat-shield, what thickness would be used up? Or might a ceramic insulator be able to handle it? What would happen if the nose was solid aluminium?How can this be calculated? What information do I need to figure this out?
  17. G

    If a person passes near me at Mach 2 speed would I see him?

    If a person is moving at Mach2 (1522 mph/h , 2469.6 km/h) and he passes close by me in a radius of 2-3 meters, would I be able to see him? Please for the sake of the question, ignore sound effects, sound barrier details etc. I'm only interested in the speed and the visual part. IF yes, what...
  18. C

    Relationship between Mach number and Reynolds number

    Is there any correlation between Mach number and Reynolds number? Both of these nondimensional numbers involve speed, but they don't seem all that related other than that. For high speed flow, we have high Mach number. Is it incorrect to say that "generally" high speed flow is turbulent?
  19. K

    Validity of Navier-Stokes at Extreme Mach Nos. (M = 100,000)

    So, speaking theoretically, if you could accelerate a fluid to extreme Mach number at sea level, then at what point does the Navier Stokes number lose its validity? What equations would you then use to model this potentially extreme momentum? I presume based on the fact that Newton's Law's are...
  20. evan-e-cent

    At what pressure does steam exiting a nozzle reach mach 1

    I am planning to build a Hero's steam engine or Aeolipile. This is the steam engine invented by the Greeks about 2000 years ago. It is attributed to Hero or Heron (10-70 AD) but was also referred to in 15 BC. My grandfather build one for a show. I have inherited it but rather than try to repair...
  21. RabbitWho

    How attention affects perception - Mach and Stumpf

    This is a bit of a logic problem that should be figure-outable from the information At the turn of the last century there was a debate about whether attention increased the perception of something by increasing the clarity of that one thing, or by decreasing the clarity of everything except...
  22. jk22

    Mach zehnder : a test for superposition ?

    We consider a one photon experiment. If the photon really follow both path at the first beam splitter then only one detector will click, if on the other hand the photon would have to choose one path (classical particle) then both detector could click ?
  23. B

    What is the aerodynamic drag of an object traveling at high supersonic velocity?

    Hello everyone. Recently I have had a lingering need to (in a loose sense) conceptualize the aerodynamic resistance of an object traveling at high supersonic velocity. However it has been a long time and I am rusty on my physics. I am looking for a ballpark figure on the Newtons and Joules (1...
  24. 8eou8elisi

    Pressure Impulses during Supersonic Flight

    Hey Everyone. I am new to this forum, so first of all greetings to everybody. What are your thoughts on the below idea..? Is it possible to make the pressure impulses created by a Supersonic Aircraft to travel faster than the speed of Sound? I know that the pressure impulses during a Supersonic...
  25. S

    C-D Nozzle - Mach No. >1 at Throat

    Hi, As I understand, it is theoretically impossible to have a Mach No. higher than one at the throat of a Convergent Divergent Nozzle. I'm currently working on some calculations, and while I've been told the calculations are correct, I'm getting abnormally high Mach Numbers at the throat...
  26. A

    Center of mass using Mach's restatement of Newtonian Mechanics

    Homework Statement Use Mach’s restatement of Newtonian mechanics to show that if we define the centre of mass of two particles according to, ⃗ r = (m1 ⃗ r1 + m2 ⃗ r2) / (m1 + m2) then the center of mass moves according to the equation, ⃗r = [(m1 ⃗u1 + m2 ⃗u2) / (m1 + m2)]t + ⃗r0 where ⃗r0 is...
  27. J

    TI89 calculator solver in functions?

    I was wondering if it's possible to use the TI89 Titanium's built-in solver with programs. More specifically, for compressible flow problems, I'd like to calculate mach number based on area ratio, specify whether the flow is subsonic or supersonic, then do something with the corresponding...
  28. LaReina

    What is the Relationship Between Mach Number and Velocity in Compressible Flow?

    Homework Statement An object is flying through the air at M=0.5. The free stream temperature is equal to 180 K. At what speed should the object fly when the temperature is 100 K in order to maintain the same Mach number? (therefore ensuring compressibility effects are the same). What was the...
  29. M

    How/Why does the Mach principle define what is a 'direction'?

    I now have a general understanding of relativity but it threw up a few issues. I understand that there are no 'fixed' points of reference in the universe, which of course begs the question as to why inertia exists. The way I imagine it is if I am the only matter in the universe, then why should...
  30. N

    Low Mach Numbers: Incompressible flow or fluid

    Hi When we talk about a fluid moving at low Mach numbers, it is said to be incompressible. But does this mean that the flow is incompressible (i.e., material derivate is zero) or does it imply that the fluid itself is incompressible (constant density)? If anybody has a reference (book...
  31. chasrob

    How Can a Superpowered Character Control Their Abilities to Avoid Catastrophe?

    Yep, half light speed or thereabouts; superhero story :). I'm writing a story about this fellow who gets super powers, including super speed. He can move, fly, at up to 100 000 miles per second. He can also move around at normal speed if he concentrates on what he's doing. Right after he...
  32. J

    A plane traveling at mach 2.5.

    Homework Statement A plane is traveling at Mach 2.5. An observer on the ground hears the sonic boom 1.0min after the plane passes directly overhead. What is the plane's altitude? Ignore the change in the speed of sound with the altitude. Homework Equations v=d/t 1/T= fThe Attempt at a...
  33. D

    Why Does a Projectile Create a Trailing Mach Cone?

    I understand why the leading edge of a projectile creates a Mach cone in front of which the air is undisturbed. But apparently the trailing edge of the projectile also creates its own Mach cone behind which the air is undisturbed. I don't understand why this is the case.
  34. PhysicoRaj

    Reaching Mach 1: Detecting Sonic Velocity in a Convergent Nozzle

    How do you know if a convergent nozzle has reached the exit velocity of mach 1? Suppose a convergent nozzle is connected to a blower, and gradually the blower air velocity is increased, would any phenomenon be helpful in detecting when the nozzle exit velocity is sonic, which can be heard or...
  35. S

    Air Molecules at Mach 1: Understanding Collisions and Net Velocity

    If molecules generally move at sound speed, given they are accelerated at Mach 1, does this mean there are less arbitrary collisions? or less collisions in general and more molecules move in the direction of mach 1 speed??
  36. chasrob

    Mach 6 at Low Altitude: Craft Skin, Booms & Visibility

    A cruise missile, small--say 10 feet long, making 4000 mph at 1 mile altitude- Would it make a boom loud enough to break windows? The smaller the craft, the less the boom, correct? Probably would be a tough one to answer; no aircraft I'm aware of is that small, making that kind of speed. The...
  37. S

    Exploring the Mach Principle: Books to Help You Understand

    some books mention one of a basis of GR is mach principle i study some text but i can't actually realize it please explain it for me or introduce some books to refer them thanks
  38. T

    Solving for shock wave angle using Mach and deflection angle

    I am trying to show how the shock wave angle varies as I hold the deflection angle constant and increase the Mach number. I am trying to solve for Beta (shock wave angle) using the theta-beta-mach relation: tan(θ)= 2cot(β) * (M2sin2(β)-1) / (M2(1.4+cos(2β))+2) This seems like it should be...
  39. P

    Modern Philosophical Science Books(a very old example would be Mach)

    Einstein drew much of his inspiration for his reworkings of space and time from philosophical books such as those written by Ernst Mach. Are there any modern philosophical science books that focus on the dilemmas of today's physics (hopefully that are respectable and not completely wacky)...
  40. L

    Calculating Reflected Pressures in Mach Reflection Region

    Hello guys, I want to compute reflected pressures in Mach reflection region. In Mach reflection, let's just think about the reflected, incident and merged pressures (of Mach stem). You know, the merged pressure is created by coalescing the incident and reflected pressures. Assuming that all...
  41. S

    Supersonic plane at mach 3

    Homework Statement A supersonic plane flies at Mach 3 at an altitude of 20,000 m. A person on the ground sees the plane directly overhead. How much time passes the before she hears the sonic boom? Homework Equations f=fo(v+-vo/v-+vs) The Attempt at a Solution I don't really know...
  42. U

    Can mach number increase from 1.8 to 1.22 in Fanno flow?

    In a problem in our book, it says that the mach number in a constant area duct with friction (Fanno flow), the mach number increases from 1.8 to 1.22...however, from the Fanno line, its very clear that in the supersonic region, mach number always decreases along the flow...is there some kind of...
  43. W

    Is it possible to have a Mach number greater than 1 at the throat?

    I have a question on Gas Dynamics, we were going over a problem in class in which the problem asks to solve for the Mach number at the throat of a converging-diverging nozzle. I assumed that the Mach at the throat should be equal to 1 since the professor said it was impossible to have a Mach...
  44. W

    Is it possible to have a Mach number greater than 1 at the throat?

    I have a problem for my Gas Dynamics homework, in which the problem asks to solve for the Mach number at the throat of a converging-diverging nozzle. I assumed that the Mach at the throat should be equal to 1 since the professor said it was impossible to have a Mach number greater then 1 at...
  45. N

    What would happen when a jet travelling at Mach 10 experiences engine failure

    If a hypersonic jet (Mach 10) were to experience sudden engine failure at high altitude what would happen? Would it continue traveling forward, slowly decelerating and descending, thereby giving the pilot chance to attempt a controlled engine restart? Or would the jet experience catastrophic...
  46. A

    Flying at the Speed of Sound: What Would a Human Feel?

    If a human were to wear a jetpack and could fly at the speed of sound, what would he feel? Would he feel the sound waves piling up on his head? What would he hear? Inside supersonic aircraft he would hear nothing, and anyone outside would hear the pressure wave, but, what if his head is the...
  47. Bob3141592

    Inflation, Mach's Principle & the Early Universe

    As I understand it, somewhere close to the beginning of the universe, the universe experienced an inflationary phase when the space 'underneath' object began to expand faster than c, the speed of light. Since it wasn't the objects themselves that were expanding, there was no violation of the...
  48. R

    Flight Mach number in terms of fuel flow rate and other parameters

    I've posted on here in relation to an aerospace analysis project I'm doing. I'm stuck on one part of the project where I need to develop the performance envelope of the turbojet engine. 3 of the 9 plots that are required are Thrust vs. Mach number. On each of those plots I'll about 7 different...
  49. J

    Is this demonstration of the book from Ernst Mach correct?

    ¿Is this demonstration of the book from Ernst Mach correct? I am reading the book "The science of mechanics", Ernst mach. He is talking about the achievements of Christian huygens, and he wants to calculate the centripetal acceleration of a circular motion. As you can see in the image...
  50. S

    Plotting Mach number as a function of Area ratio

    Homework Statement A=0.1+x^2 in a convergent -divergent nozzle .I need to plot mach number as a function of x for isentropic flow across the nozzle. I know the A/A* as a function of Ma. But finding the opposite (Ma in terms of A/A*) from that equation did not seem to be that easy...