Operating System Design - Operating System Structures

Operating System Services

 

User interface

Program execution

I/O operation

File-system manipulation

Communications

Error detection

Resource allocation

Logging

Protection and security

 

System Call

 

Programming interface to the services provided by the Operating System

Mostly accessed by programs via a high-level API rather than direct system call use

 

Typically, a number associated with each system call (System-call interface maintains a table indexed according to these numbers)

Most details of OS interface hidden from programmer by API

 

1. User application call API

2. API call corresponding system call (interrupt)

3. CPU saves current process' state into the PCB block and give CPU resource to OS

4. OS jumped to kernel mode

5. OS dispatch the interrupt with corresponding interrupt handler by using interrupt vector

6. After the system call finished, it makes interrupt to the interrupt request line in CPU

7. CPU check it and restored the original process state in PCB block

8. The original process gets CPU resource and continues the code

System Call Parameter Passing

 

Methods : 

Pass the parameters in register

Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register

Parameters placed or pushed onto the stack by the program and popped off the stack by the operating system

 

Types of System Calls

 

Process control, File management, Device management, Information maintencance, Communications, Protection

 

System Services

 

File manipulation

Status information sometimes stored in a file

Programming language support

Program loading and execution

Communications

Background services

Application programs

 

Most users’ view of the operation system is defined by system programs, not the actual system calls

 

Linker and Loader

 

Relocatable object file : source code compiled into object files designed to be loaded into any physical memory location

Linker : conbines relocatable object file into single binary executable file

Loader : loads executable file into memory and, set up program counter into entry point of executor file

 

Operating System Structure

 

Monolithic Structure (Original UINX) : consists of Systems programs and the kernel (Provides the file system, CPU scheduling, memory management, and other operating-system functions)

Layered Approach : The operating system is divided into a number of layers (levels), each built on top of lower layers

With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

Microkernels : Moves as much from the kernel into user space

   Benefits : Easier to port the operating system to new architectures

   Detriments : Performance overhead of user space to kernel space communication

Modules : Uses object-oriented approach, Each core component is separate, Each talks to the others over known interfaces