options A,C,D are correct only B is not true hence ans is B
Some key features of the Unix architecture concept are:
- Unix systems use a centralized operating system kernel which manages system and process activities.
- Unix systems are preemptively multitasking: multiple processes can run at the same time, or within small time slices and nearly at the same time, and any process can be interrupted and moved out of execution by the kernel. This is known as thread management.
- Files are stored on disk in a hierarchical file system, with a single top location throughout the system (root, or "/"), with both files and directories, subdirectories, sub-subdirectories, and so on below it.
- With few exceptions, devices and some types of communications between processes are managed and visible as files or pseudo-files within the file system hierarchy. This is known as everything is a file. However, Linus Torvalds states that this is inaccurate and may be better rephrased as "everything is a stream of bytes".