System calls and OS structure

Question 1

What are the two main functions of an operating system?

Answer 1

• Providing abstractions to user programs.
• Managing the computer’s resources.

Question 2

What does the interface between user programs and the operating system primarily deal with?

Answer 2

Dealing with abstractions such as file creation, writing, reading, and deletion.

Question 3

What is the purpose of system calls in the operating system?

Answer 3

System calls allow user programs to request services from the operating system, such as reading data from a file.

Question 4

How are system calls invoked from C programs?

Answer 4

System calls are typically invoked by calling library procedures with the same name as the system call.

Question 5

What happens when a process makes a system call?

Answer 5

The process executes a trap instruction to transfer control to the operating system, which carries out the system call and returns control to the instruction following the system call.

Question 6

How does the operating system determine the requested service in a system call?

Answer 6

The operating system inspects the parameters passed by the calling process to determine the specific system call and its required actions.

Question 7

What is the purpose of the TRAP instruction in the system-call mechanism?

Answer 7

The TRAP instruction switches the processor from user mode to kernel mode and starts execution at a fixed address within the kernel.

Question 8

How are system calls handled by the operating system?

Answer 8

The system-call handler, determined by the system-call number, is invoked to perform the requested service.

Question 9

What happens if a system call encounters an error or invalid parameter?

Answer 9

The system call sets the return value to -1 and stores the error number in a global variable called errno.

Question 10

How does the fork system call work in the process management of an operating system?

Answer 10

The fork system call creates an exact duplicate of the original process, including all its resources, and returns the process ID (PID) of the child to the parent.

Question 11

What are the three system calls related to directory managemente?

Answer 11

mkdir
rmdir
link

Question 12

What is the purpose of the mkdir system call?

Answer 12

The mkdir system call is used to create a new empty directory.

Question 13

How does the link system call work?

Answer 13

The link system call allows the same file to appear under two or more names in different directories.

Question 14

How does the rmdir system call function?

Answer 14

The rmdir system call is used to remove an empty directory from the file system.

Question 15

What happens when a file is linked using the link system call?

Answer 15

When a file is linked, changes made to the file by any user are instantly visible to other users who have access to the file. It creates multiple directory entries that refer to the same file.

Question 16

What happens if one of the linked directory entries is removed using the unlink system call?

Answer 16

If one of the linked directory entries is removed using the unlink system call, the other linked entry remains unaffected.

Question 17

How does the mount system call work in UNIX?

Answer 17

The mount system call allows two file systems to be merged into one.

Question 18

What is the purpose of the chdir system call?

Answer 18

is used to change the current working directory of a process.

Question 19

What does the chmod system call do?

Answer 19

changing the mode of a file, which includes modifying the read-write-execute permissions for the owner, group, and others.

Question 20

What is a monolithic operating system structure?

Answer 20

In a monolithic system, the entire operating system runs as a single program in kernel mode. It is written as a collection of procedures linked together into a large executable binary program.

Question 21

What are the advantages and disadvantages of a monolithic system?

Answer 21

+ efficient as procedures can call any other procedure directly

+ simple and straightforward design

• can become unwieldy and difficult to understand due to the unrestricted interaction between procedures.
• a crash in any procedure can cause the entire OS to crash.

Question 22

Describe the layered system structure.

Answer 22

A layered system organizes the OS as a hierarchy of layers, where each layer is built upon the one below it. Each layer provides a specific functionality, and higher layers utilize services provided by lower layers.

Question 23

What was the purpose of the THE system’s layered approach?

Answer 23

used layers to provide abstraction and isolation between different aspects of the system

Question 24

How does the microkernel structure differ from the monolithic structure?

Answer 24

the OS is split into small, well-defined modules.

only runs in kernel mode while other components run as user processes.

Question 25

What are some advantages of using a microkernel?

Answer 25

better reliability as bugs in user processes are less likely to crash the system

flexibility by allowing dynamic loading and unloading of components

Question 26

How does the client-server model differ from the microkernel structure?

Answer 26

OS distinguishes between client processes and server processes. clients request services from servers by sending messages, and servers provide those services