Privileged instructions are a crucial aspect of computer programming that often goes unnoticed. These instructions, also known as privileged operations, are a set of commands that can only be executed by the operating system or kernel. In this article, we will delve into the concept of privileged instructions and understand their significance in computer systems.
To begin with, let us first understand the term 'privilege' in the context of computer systems. In simple terms, privilege refers to the level of access or authority a user has over the system. In a multi-user environment, different users have different levels of privilege, depending on their role and responsibilities. For instance, a regular user has limited access to the system, while the system administrator has complete control over it.
Now, coming back to privileged instructions, these are a set of commands that can only be executed by the operating system or kernel. These instructions are considered 'privileged' because they have the authority to perform critical operations that can potentially harm the system if executed incorrectly. Some examples of privileged instructions include I/O operations, memory management, and interrupt handling.
One might wonder, why have privileged instructions in the first place? The answer lies in the protection and security of the system. Privileged instructions help in preventing unauthorized access to critical system functions. For instance, if a regular user tries to execute an I/O operation, the system will deny the request as it does not have the privilege to do so. This ensures that only authorized users can access and manipulate crucial system resources.
In most computer systems, privileged instructions are divided into two categories - user mode and kernel mode. User mode is the default mode in which applications and programs run. In this mode, only a limited set of instructions can be executed, and any attempt to execute a privileged instruction will result in an exception. On the other hand, the kernel mode is a privileged mode in which the operating system executes. In this mode, all instructions can be executed, including privileged ones.
Now, let us understand how privileged instructions are executed. When a program attempts to execute a privileged instruction, an exception is generated, and the control is passed to the operating system. The operating system then checks the privilege level of the program and determines whether the instruction can be executed or not. If the privilege level is appropriate, the instruction is executed, and the control is returned to the program. If not, an error message is displayed, and the program is terminated.
It is essential to note that while privileged instructions are crucial for the security of the system, they can also be exploited by malicious programs to gain unauthorized access. To prevent this, modern processors have implemented hardware-based security features, such as privilege levels and access control mechanisms, to ensure that only authorized programs can execute privileged instructions.
In conclusion, privileged instructions play a crucial role in maintaining the security and integrity of computer systems. By restricting access to critical operations, they prevent unauthorized users from manipulating the system. However, with the constant advancements in technology, the concept of privileged instructions is continually evolving, and it is essential for programmers and system administrators to stay updated with these changes to ensure the smooth functioning of their systems.
