Operating system architecture

Classification of OS
Functions of OS
Key components
OS Architecture
Family of OS
Useful Links



     The computer architecture of a computing system defines its attributes as seen by the programs that are executed in that system, that is, the conceptual structure and functional behavior of the machine hardware. Then, the computer architect defines the functions to be executed in the hardware and the protocol to be used by the software in order to exploit such functions. Note that the architecture has nothing to do with the organization of the data flow, the logical design, the physical design, and the performance of any particular implementation in the hardware.

      Hence By Architecture we mean the order in which certain hardware Processes are carried out by the OS and has nothing to do with the logical software flow of the Computer.

Simple view

An Operating System is the layer between the hardware and software, as in

An Operating System is responsible for the following functions

  • Device management using device drivers
  • Process management using processes and threads
  • Inter-process communication
  • Memory management
  • File systems

In addition, all operating systems come with a set of standard utilities. The utilities allow common tasks to be performed such as

  • being able to start and stop processes
  • being able to organise the set of available applications
  • organise files into sets such as directories
  • view files and sets of files
  • edit files
  • rename, copy, delete files
  • communicate between processes


The kernel of an operating system is the part responsible for all other operations. When a computer boots up, it goes through some initialisation functions, such as checking memory. It then loads the kernel and switches control to it. The kernel then starts up all the processes needed to communiate with the user and the rest of the environment (e.g. the LAN)

The kernel is always loaded into memory, and kernel functions always run, handling processes, memory, files and devices.

The traditional structure of a kernel is a layered system, such as Unix. In this, all layers are part of the kernel, and each layer can talk to only a few other layers. Application programs and utilities live above the kernel.

The Unix kernel looks like Unix kernel

Most of the Operating Systems being built now use instead a micro kernel, which minimises the size of the kernel. Many traditional services are made into user level services. Communication being services is often by an explicit message passing mechanism.

The major micro-kernel Operating System is Mach. Many others use the concepts of Mach. Mach kernel

Some systems, such as Windows NT use a mixed approach NT kernel





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