Cse 331 Lecture Slides

OS Services cont…

• Communication
• Data transfer between processes may be required from time to time
• The processes may be on one computer or different computer connected over a computer network
• Error Detection
• Errors may occur in the CPU, I/O devices or in memory devices
• The OS constantly needs to be aware of possible errors
• It should take the appropriate action to ensure correct and consistent computing
• Accounting
• To keep track of which users use how much and what kinds of computer resources

OS User Interface

• Command Interpreter
• CLI allows direct command entry
• Fetches a command from a user and executes it
• They are either implemented in kernel or by systems programs
• Eg Linux shell, Windows shell
• GUI
• User friendly desktop metaphor interface
• Files, programs, action etc are represented using icons
• Mouse action over objects on the interface cause various actions (Provide information, option, execute function, open directory etc)
• Many systems now include both CLI and GUI interfaces

System Calls

• System calls provide the interface between a process and the

operating system.

• These calls are generally available as assembly-language instructions.
• Typically written in a high-level language (C or C++)
• allow user-level processes to request some services from the operating system.
• E.g. for I/O a process involves a system call telling the operating system to read or write particular area and this request is satisfied by the operating system.

System Calls cont..

• The following different types of system calls provided by an OS:

• Process control
• End, abort
• Load, execute
• Create, terminate
• Get attributes, set attributes
• Allocate, free memory

• File management
• Create, delete
• Open, close
• Read, write
• Get file attributes, set file attributes

• Device management
• Request, release device
• Read, write
• Get attributes, set attributes
• Logically attach or detach devices

• Communication
• Create, delete communication connection
• Send, receive message
• Transfer status information
• Attach or detach remote devices