ALSTOM Technical Lead interview questions

1)At first they initially asked me to give a brief introduction which i did give .Once introduction was done ,they just jumped to Linux questions some of which i remember are as mentioned below: 2)What is difference between message passing and message queing. 3) what is the difference between Linux and QNX? 4)What is the size of an integer and who determines the size of an integer. 5)Another tricky question asked was that why is shared memory IPC slowest among the three IPC's. 6)Which would you think would be able to access faster a)Global variable or a shared memory variable b)Local variable or a shared memory variable and why? 6)What is structure padding and why padding is used and how can we disable structure padding? 7)Have you used Mutex and where and why cant we use binary semaphore instead of mutex?