1. What is the difference between application and system programming?
   Application programming focuses on solving a problem for the final user, while system programming is about creating software used by other software.
2. What is an API? Why are APIs so important?
   An API is an interface that the software exposes to control the access to the resources it controls. It is a description of how other applications should communicate with the software.
3. Could you explain how protection rings work?
   Protection rings are a system used to prevent failures and increase security. They arrange security in hierarchical levels with growing limitations and allow a mediate access to the features of the more powerful levels by using specific gateways.
4. Can you provide some examples of what cannot be undertaken in user space?
   An application in user space cannot change its current space to kernel, cannot access the hard drive ignoring the filesystem, and cannot change the page tables.
5. What's a system call?
   System calls are the API provided by the operating system to access the machine's resources.
6. Which calls are used in Unix to manage a process?
   The calls that Unix uses to manage a process are as follows: fork, exit, and wait.
7. Why is POSIX useful?
   The various POSIX standards define process controls, signals, segmentation, illegal instructions, file and directory operations, pipes, I/O control and the C library, shells and utilities, and real-time and multithreaded extensions. It is extremely useful for a developer when building applications, because it aids in building an application that works with different operating systems sharing this standard.
   
8. Is Windows POSIX-compliant?
   Windows is not POSIX-compliant, but an attempt is being made to offer a POSIX framework, such as the Windows Linux subsystem.