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Questions and Answers
Which mode has the highest privilege level?
Which mode has the highest privilege level?
- Supervisor mode (correct)
- User mode
- Kernel mode
- Restricted mode
User mode can access any memory area.
User mode can access any memory area.
False (B)
What type of programs run in the supervisor domain?
What type of programs run in the supervisor domain?
Kernel programs
In the relationship between protection domains, user mode is usually a __________ of supervisor mode.
In the relationship between protection domains, user mode is usually a __________ of supervisor mode.
Which operation is restricted in user mode?
Which operation is restricted in user mode?
Match the protection domain with its description:
Match the protection domain with its description:
Programs in supervisor mode cannot directly interact with hardware devices.
Programs in supervisor mode cannot directly interact with hardware devices.
What is typically used to enforce protection domains?
What is typically used to enforce protection domains?
Which protection ring in x86 architecture has the highest privilege level?
Which protection ring in x86 architecture has the highest privilege level?
What is the primary role of the CPU in relation to memory?
What is the primary role of the CPU in relation to memory?
ARMv7 has more privilege levels than x86 architecture.
ARMv7 has more privilege levels than x86 architecture.
What are the two primary protection domains used by most operating systems?
What are the two primary protection domains used by most operating systems?
Isolation operations in operating systems are used to allow all applications unrestricted access to the system resources.
Isolation operations in operating systems are used to allow all applications unrestricted access to the system resources.
In ARMv8 architecture, the number of privilege levels is ______.
In ARMv8 architecture, the number of privilege levels is ______.
What term describes the communication layer that links different components of a computer?
What term describes the communication layer that links different components of a computer?
What is the purpose of processor privilege levels?
What is the purpose of processor privilege levels?
In an operating system, critical operations that could break the system if done improperly are isolated in ___________ domains.
In an operating system, critical operations that could break the system if done improperly are isolated in ___________ domains.
User mode operations can be performed in supervisor mode.
User mode operations can be performed in supervisor mode.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
Match the following privilege levels with their corresponding architecture:
Match the following privilege levels with their corresponding architecture:
Which of the following is NOT a reason for the need for isolation in operating systems?
Which of the following is NOT a reason for the need for isolation in operating systems?
Explain the significance of protection domains in operating system architecture.
Explain the significance of protection domains in operating system architecture.
Operating systems trust all user applications to operate safely without supervision.
Operating systems trust all user applications to operate safely without supervision.
What can happen if a user application modifies the state of a critical device improperly?
What can happen if a user application modifies the state of a critical device improperly?
Supervision mode is also known as ______ mode.
Supervision mode is also known as ______ mode.
Developers can write user applications regardless of their ___________ level, which poses security risks.
Developers can write user applications regardless of their ___________ level, which poses security risks.
Which of the following architectures provides four privilege levels?
Which of the following architectures provides four privilege levels?
Which statement best reflects the purpose of protection domains in an operating system?
Which statement best reflects the purpose of protection domains in an operating system?
What level must an application switch to for executing privileged features?
What level must an application switch to for executing privileged features?
ARMv7 platforms utilize a ring -1 level for privileged instructions.
ARMv7 platforms utilize a ring -1 level for privileged instructions.
Name the two processor privilege levels needed for x86 applications.
Name the two processor privilege levels needed for x86 applications.
Applications running in user mode perform a _____ to access privileged operating system services.
Applications running in user mode perform a _____ to access privileged operating system services.
Match the following terms with their definitions:
Match the following terms with their definitions:
Which mode allows user applications to run with limited privileges?
Which mode allows user applications to run with limited privileges?
The kernel operates in user mode to perform privileged operations.
The kernel operates in user mode to perform privileged operations.
What is the primary responsibility of the kernel in an operating system?
What is the primary responsibility of the kernel in an operating system?
In an operating system architecture, the ______ runs in supervisor mode.
In an operating system architecture, the ______ runs in supervisor mode.
Match the following operations with their corresponding system call category:
Match the following operations with their corresponding system call category:
Which of the following is NOT a component of the kernel?
Which of the following is NOT a component of the kernel?
System calls validate the arguments passed by the program to ensure they are not forged pointers.
System calls validate the arguments passed by the program to ensure they are not forged pointers.
Name the two modes in which an operating system runs.
Name the two modes in which an operating system runs.
User applications can only perform privileged operations through the ______ code.
User applications can only perform privileged operations through the ______ code.
What is the purpose of protection domains in an operating system architecture?
What is the purpose of protection domains in an operating system architecture?
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Study Notes
Protection Domains
- Two main protection domains exist: Supervisor Mode (S mode) and User Mode (U mode).
- These domains define different privilege levels, which determine access to system operations.
Supervisor Mode (S Mode)
- Highest privilege level, allowing unrestricted access to system resources.
- Programs can execute all CPU instructions, directly interact with hardware, and access any memory area.
- Used by the operating system's kernel, which contains essential low-level components.
User Mode (U Mode)
- Lowest privilege level, imposing restrictions on operations.
- Programs are prohibited from executing privileged instructions that alter system state or access restricted memory areas.
- Employed by user applications and high-level operating system services outside the kernel.
Relationship Between Protection Domains
- User mode is considered a subset of supervisor mode.
- Essential communication occurs through a bus connecting the CPU, devices, and memory, enabling operations like displaying data or network actions.
Need for Isolation
- Certain operations, if improperly executed, could destabilize the system, such as modifying device states or accessing restricted memory.
- User applications, which may be written by unskilled or malicious programmers, necessitate isolation by the operating system to ensure system security.
Processor Privilege Levels
- Protection domains are implemented via hardware processor privilege levels, known as CPU modes or states.
- The x86 architecture offers four protection rings, while ARMv7 has three and ARMv8 provides four levels.
- Within x86, Ring 0 is the most privileged, while on ARMv7, PL0 is the least privileged.
Matching Protection Domains to Privilege Levels
- Most operating systems operate using two protection domains (user and supervisor) to control access securely.
- System calls are methods that enforce checks to ensure programs have permission to access certain resources and that argument validity is maintained.
Operating System Architecture
- User applications and high-level services execute in user mode; the kernel operates in supervisor mode.
- Protection domains require only two privilege levels as per the Instruction Set Architecture.
Virtualization Context
- In virtualized systems, hypervisors employ an additional instruction level, with x86 using a new ring -1 and ARMv7 using PL2.
Switching Between Modes
- User applications must shift to supervisor mode for access to privileged features, achieved through system calls.
- These system calls facilitate a controlled interface between user applications and privileged operating system services.
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