Operating System Structures - Operating System - Lecture Slides, Slides of Computer Science

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Chapter 2: Operating-System

Structures

• Operating system design
• Interface provided to users & programmers
  • System calls (programmer access)
  • User level access to system
• Services

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System Structure

• Layered approach
  • Operating system divided into layers
  • Higher levels use only services of lower levels
  • Basic principle of abstract data types (classes)

Figure 2.

Example

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BlockLinkedList

BlockGroup FreeList

Directory

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Original Unix O/S:

Kernel Approach

Figure 2.13, p. 69 “monolithic structure” Docsity.com

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Microkernel Approach

• More like a client-server system
• Kernel supports efficient message passing
  • Plus some other low-level services such as interrupt handling, loading device drivers
• Much of former kernel runs in user mode (not kernel mode) - E.g., file system (server) may run in user mode
• Mach (some versions), and QNX (http://www.qnx.com/) operating systems organized this way
• QNX is real-time; small (micro) kernel can be advantageous to real-time systems

8 http://en.wikipedia.org/wiki/Microkernel Docsity.com

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Mac OS X: “Microkernel”

Approach (not fully)

Figure 2.

Emphasis : Mach and BSD Unix both run in kernel mode

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Solaris: Modular approach

• “Perhaps the best current methodology for operating-system design involves using object- oriented programming techniques to create a modular kernel” (p. 72)
• modules are typically dynamically loadable (e.g., Solaris, Linux, Mac OS X)

Fig 2.

Process Interfaces to the System

• In what we’ve been talking about so far, a

process can either execute machine

language code or it can make system calls

• What other kinds of process interfaces are

possible?

• API or library interfaces; e.g., POSIX
• Virtual machine interface

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Virtual Machines

• Processes provided with an interface virtually identical to the bare hardware
• Each process is provided with a (virtual) copy of the underlying computer
• E.g., IBM VM mainframe operating system
• Devices are an issue
  • e.g., Disks must be partitioned
• Each user runs an operating system on their own virtual machine - Some instructions run directly on hardware - Some instructions (e.g., I/O) are interpreted

Hosted Virtual Machine

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Java Virtual Machine (JVM)

• Specification for an abstract computer
  • http://java.sun.com/docs/books/jvms/
  • http://java.sun.com/docs/books/jvms/second_edition/html/VMSpecTOC.doc.html
• Instructions specified as “bytecode”s
• Architecture neutral
• Java program code is compiled (javac) into files containing bytecode
• JVM includes
  • Class loader
  • Bytecode verifier
  • Bytecode interpreter

Services - 1

• User Interface
  • GUI and command line are the most common for general purpose operating systems
• Program execution
  • System must be able to load a machine language program into RAM memory and run that program
• Resource allocation
  • Multiple processes or users: Need to share, allocate, and manage resources
  • Examples of types of resources: CPU cycles (time), main memory, disk files, I/O devices (printers, USB flash drives etc). 20

Services - 2

• I/O operations
  • All I/O that a program does is typically carried out by the O/S
  • This is for efficiency and protection
• File-system manipulation
  • creating, reading, writing files & directories
• Communications
  • Between processes on the same computer and between processes across different computers
  • e.g., Shared memory & message passing 21