CIS 307: Views, Components, and Architectures of Operating Systems

[Introduction], [Resource Manager], [Virtual Machine], [Responsive System], [Components], [Monolithic Architecture], [Layered Architecture], [Virtual Machine Architecture], [Micro-Kernel Architecture]

Introduction

Here is a possible definition of an Operating System (paraphrased from Brinch Hansen):
An Operating System is a set of manual and automatic procedures that enable a group of people to use a computer installation efficiently.
The word Efficiently is very ambiguous. What are the Objective Functions to be used to evaluate efficiency? Here are some possibilities:

• Functionality
• Performance: Time (Response Time=Turnaround Time, Latency), Utilization (CPU, Memory, I/O, Communication Channels, ..)
• Convenience

Of course these objective functions may not all agree. For example, cost and functionality may conflict, as well as response time and utilization.

Resource Manager

• Processors, Main memory, Secondary Memory, Devices, Information.

• Efficiency, Protection, Security, Privacy, Reliability.

or alternatively

Responsive System

Components

• Process Management: Create/Delete/Suspend/Resume Processes, Inter Process Communication (IPC)
• Memory Management: Allocate and Deallocate Physical Memory
• Virtual Memory Management: Maintain mapping from virtual to physical memory, decide on size of memory to allocate to processes, enforce replacement policy
• I/O Management: definition of Device Drivers providing a uniform interface to devices
• Secondary Storage Management: allocation and deallocation of blocks, recovery block management.
• File Management: naming, directories, creation, use, and deletion of files, locks, protection, backups, accounting.
• Network Services: support for various protocols and communication facilities.
• Command Language Interpreter(CLI): interface to operator and users that gives them the ability to give commands to the OS.
• Information Services: Show/Set commands
• Accounting Services: Quotas, usages, and Costs.

A monolithic kernel can be easy to implement if we are ready to accept very high latency [i.e. we service requests withour worrying about the urgency of other requests], otherwise it may be with a structure that is very difficult to understand. Monolithic kernels are an architecture whose time has come and gone.

Layered Architecture

It is not always easy to have a truly layered architecture since some functionalities are naturally described as mutually dependent. In addition a layered architecture is often inefficient since it requires a high number of traversals of interfaces.

Virtual Machine Architecture (VM370)

The virtal machine architecture is elegant, but it does not deal with the questions of resource management, or of responsiveness.

Micro-Kernel Architecture

The micro-kernel architecture strives to take out of the kernel as much functionality as possible, so as to limit the code executed in privileged mode and to allow easy modifications and extensions. The micro-kernel architecture allows us to build a number of different operating systems all using the same micro-kernel, Each operating system will make use of different system processes. Notice that little is in the kernel. But what is there has great importance. Interactions between processes involve kernel intervention. Thus the efficiency of the transfer from user to kernel mode and back must be very high. Many believe that this architecture is inherently inefficient and that the use of a more extensive but pre-emptible kernel is preferable.

http://www.cis.temple.edu/~ingargio/cis307/readings/intro.html