Question

Q3. What is the major difference between single quotes and double quotes? Explain each with a proper example. Q4. 121 How user application program request any services from the kernel of the operating system? Explain all its process briefly.

Answer 1

Note: In third question, you didn't clear the language name in which we have to explain the difference, please let me know in which concern you want the difference, i will edit the answer for question 3 according to you. Thanks.

Answer 4:

A system call is a mechanism that is used by the application program to request a service from the kernel of the operating system. They use a machine-code instruction that causes the processor to change mode. An example would be from supervisor mode to protected mode.

Process:

When a program makes a system call, the mode is switched from user mode to kernel mode. This is called a context switch.

Then the kernel provides the resource which the program requested. After that, another context switch happens which results in change of mode from kernel mode back to user mode.

Generally, system calls are made by the user level programs in the following situations:

• Creating, opening, closing and deleting files in the file system.
• Creating and managing new processes.
• Creating a connection in the network, sending and receiving packets.
• Requesting access to a hardware device, like a mouse or a printer.

In a typical UNIX system, there are around 300 system calls. Some of them which are important ones in this context, are described below.

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