SCC.131 Digital Systems - System Calls

Flashcards about Operating Systems: System Calls

Operating System

Manages and allocates resources; performs tasks like file, memory, and process management, I/O handling, security, and multitasking.

Main Tasks of an Operating System

File management, Memory management, Process management, Input/Output handling, Security & Access Control, Multitasking & Scheduling.

Types of Kernels

Monolithic and Micro-kernels

Related to Processes/Threads

Processes and Threads

Scheduling

Ensures efficient CPU utilization and fair process execution.

System Calls

Controlled entry points into the kernel, allowing user-mode applications to request privileged operations.

Why System Calls are Essential

Communication between user programs and the OS; provides an interface for requesting OS services.

Examples of Privileged Operations Requested via System Calls

Accessing hardware, file systems, or network resources.

Examples of Operations Provided by System Calls

Process management, I/O, security, and IPC.

API in Operating Systems

Interface provided by the OS, often in C/C++, that simplifies interaction compared to raw system calls.

System Call Definition

A function call into OS code that runs at a higher privilege level of the CPU.

Higher Privilege Level Importance

Sensitive operations are allowed only at a higher privilege level.

Why a Well-Defined Mechanism is Needed

To ensure security and stability when switching from user-space to kernel-space.

Simple Overview of a System Call

Switch from user-space to kernel-space, verify security permissions, perform the system call, and switch back.

Two Classes of Entry Points to Kernel Mode

Interrupts and Exceptions

Interrupts

Generated by devices to signal needing attention.

int 0x80

Software interrupt instruction used to make system calls to the kernel (in 32-bit Linux systems).

Security Verification when Using System Calls

The OS ensures the request is secure and valid before executing it.

Primary Communication Method in Micro-Kernels

Message-passing

Per-Process Virtualized Devices

Each process interacts with its own virtual instance of a device.

Why Use System Calls?

Provides a standardized way to use hardware resources, prevents direct access to critical system resources, and simplifies complex hardware interactions.

Key Role of System Calls

Enables user programs to request services from the OS, involving a switch between user mode and kernel mode.