Operating System Services
Program execution – system capability to load a program into memory and to run it.
I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O.
File-system manipulation – program capability to read, write, create, and delete files.
Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.
Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O
devices, or in user programs.
Additional Operating System Functions
Additional functions exist not for helping the user, but rather for ensuring efficient system operations.
1. Resource allocation – allocating resources to multiple users or multiple jobs running at the same time.
2. Accounting – keep track of and record which users use how much and what kinds of computer
resources for account billing or for accumulating usage statistics.
3. Protection – ensuring that all access to system resources is controlled.
System calls provide the interface between a running program and the operating system.
1. Generally available as assembly-language instructions.
2. Languages defined to replace assembly language for systems programming allow system calls
to be made directly (e.g., C, C++)
Three general methods are used to pass parameters between a running program and the operating system.
1. Pass parameters in registers.
2. Store the parameters in a table in memory, and the table address is passed as a parameter in a register.
3. Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.
Passing of Parameters As A Table
Types of System Calls
1. Process control
2. File management
3. Device management
4. Information maintenance
At System Start-up Running a Program
UNIX Running Multiple Programs
Msg Passing Shared Memory
Communication may take place using either message passing or shared memory.