Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
System Calls in Unix and Windows
System calls provide the interface between a process and an operating system. They are available as assembly language instructions and serve as the only mechanism for user programs to access kernel services. System calls are similar to function calls but transfer control from user mode to kernel mode.
How System Calls Work
When a process needs operating system services, it makes a system call which triggers a software interrupt. The CPU switches from user mode to kernel mode, executes the requested service, and returns the result to the calling process. This mechanism ensures security and controlled access to system resources.
Unix System Calls
Unix provides around 80 system calls for file system control, process management, and interprocess communication. These system calls are the only way to access the Unix kernel from user programs.
| System Call | Description |
|---|---|
| access() | Checks if a calling process has access to the required file |
| chdir() | Changes the current directory of the system |
| chmod() | Changes the mode/permissions of a file |
| chown() | Changes the ownership of a particular file |
| kill() | Sends a kill signal to one or more processes |
| link() | Links a new file name to an existing file |
| open() | Opens a file for reading or writing |
| pause() | Suspends execution until a particular signal occurs |
| stime() | Sets the system time |
| times() | Gets the execution times of parent and child processes |
| alarm() | Sets the alarm clock for a process |
| fork() | Creates a new process by duplicating the current process |
| chroot() | Changes the root directory for a process |
| exit() | Terminates the calling process |
Windows System Calls
Windows system calls handle file operations, process management, interprocess communication, memory management, I/O devices, and security. The Windows API provides a rich set of system calls that programs use to interact with the operating system.
| System Call | Description |
|---|---|
| CreateProcess() | Creates a new process and its primary thread |
| ExitProcess() | Terminates the calling process and all its threads |
| CreateFile() | Creates or opens a file, directory, or device |
| ReadFile() | Reads data from a file or device |
| WriteFile() | Writes data to a file or device |
| CloseHandle() | Closes an open object handle |
| SetTimer() | Creates a timer that executes at specified intervals |
| CreatePipe() | Creates an anonymous pipe for interprocess communication |
| SetFileSecurity() | Sets the security descriptor for a file or directory |
| SetConsoleMode() | Sets the input or output mode of a console buffer |
| ReadConsole() | Reads character input from the console input buffer |
| WriteConsole() | Writes characters to the console screen buffer |
Comparison
| Aspect | Unix | Windows |
|---|---|---|
| Process Creation | fork() + exec() | CreateProcess() |
| File Operations | open(), read(), write() | CreateFile(), ReadFile(), WriteFile() |
| Process Termination | exit() | ExitProcess() |
| IPC | pipe(), signal() | CreatePipe(), CreateEvent() |
| Design Philosophy | Simple, minimal calls | Rich, feature-complete API |
Conclusion
System calls are essential for process-OS communication, providing controlled access to kernel services. Unix emphasizes simplicity with around 80 basic calls, while Windows offers a comprehensive API with hundreds of specialized functions. Both approaches effectively bridge user programs and system resources through secure kernel interfaces.
27K+ Views
