Chapter 2 operating system structures
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Chapter 2, Operating System Structures. 2.1 Operating System Services. Overview List: User interface Program execution File system Communications Error detection Efficiency functionality Security. User interface: Command line Batch Graphical user interface Program execution Load

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Chapter 2, Operating System Structures

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Chapter 2 operating system structures

Chapter 2, Operating System Structures


2 1 operating system services

2.1 Operating System Services

  • Overview List:

    • User interface

    • Program execution

    • File system

    • Communications

    • Error detection

    • Efficiency functionality

    • Security


Chapter 2 operating system structures

  • User interface:

    • Command line

    • Batch

    • Graphical user interface

  • Program execution

    • Load

    • Run

    • End successfully or not


Chapter 2 operating system structures

  • I/O operations

    • Access to physical devices (usually protected—a system service)

  • File system manipulation, files, directories

    • Read, write

    • Make, delete

    • Find, navigate


Chapter 2 operating system structures

  • Communications

    • Inter-process communication

    • Same computer or different systems

    • Message passing

    • Or shared memory

  • Error detection

    • In CPU

    • In memory

    • In user program

    • Detect and handle gracefully, allowing continued use of the system.


Chapter 2 operating system structures

  • O/S functions to promote efficiency, especially on multi-user systems

    • Resource allocation

      • Scheduling CPU cycles

      • memory access

      • I/O

      • file system, etc.

    • Accounting

      • How much of each resource used by each user

      • In what pattern

      • At what times

      • Billling and system configuration


Chapter 2 operating system structures

  • Protection and security

    • Logins and rwx type permissions

    • Protecting one process from another (in memory)

    • Protecting from outside intrusions


2 2 user operating system interface

2.2 User Operating System Interface

  • Overview List:

  • Command interpreter function

  • Command interpreter architecture

  • GUI

  • Choice of interface


Chapter 2 operating system structures

  • Command interpreter function

    • Setup for a command line interface

    • Gives the prompt

    • Takes in the command and takes action

  • Command interpreter architecture

    • May be part of the kernel

    • May be run as a separate program

    • May include the code to be run as subroutines

    • May call separate system programs based on the command entered


Chapter 2 operating system structures

  • GUI—no important new information here

  • Choice of interface

    • User preference

    • Note power of programming in a command line interface vs. a GUI


2 3 system calls

2.3 System Calls

  • Overview list:

    • Explicit system calls

    • Embedded system calls

    • Implicit system calls

    • Passing parameters in the system

    • System calls in Java


Chapter 2 operating system structures

  • Explicit system call

    • Example: copying a file

    • Entered from command line or through GUI

    • One user system call may result in a sequence of internal system calls

  • Embedded system call

    • In ASM, C, C++, etc., it is possible to include lines of code containing system calls


Chapter 2 operating system structures

  • Implicit system calls

    • The compiler translates user instructions to machine instructions

    • At run time, machine instructions which are protected trigger system calls

    • The classic example is file I/O


Chapter 2 operating system structures

  • Passing parameters in the system

    • Stored in registers

    • Stored in memory, memory address stored in register

    • Pushed onto the stack

  • Note that this heading is relevant to the topic of system calls

  • Various system calls require that parameters be passed when (before) the call is made


Chapter 2 operating system structures

  • System calls in Java

    • Write a method in Java declared “native”

    • Let the native method be a holder for C or C++ (system language) code

    • The C/C++ code can call system programs

    • Note that the Java code is now platform dependent, not portable


2 4 types of system calls

2.4 Types of System Calls

  • Overview List:

    • Process control

    • File management

    • Device management

    • Information management

    • Communications


Chapter 2 operating system structures

  • Process control

    • End, abort

    • Load, execute

    • Create, terminate

    • Get attributes, set attributes

    • Wait for time

    • Wait for event, signal event

    • Allocate and free memory


Chapter 2 operating system structures

  • File management

    • Create, delete

    • Open, close

    • Read, write, reposition

    • Get attributes, set attributes

  • Device management

    • Request, release

    • Read, write, reposition

    • Get attributes, set attributes

    • Logically attach or detach


Chapter 2 operating system structures

  • Information management

    • Get time or date, set time or date

    • Get system data, set system data

    • Get process, file, or device attributes

    • Set process, file, or device attributes

  • Communications

    • Create, delete communication connection

    • Send, receive messages

    • Transfer status information

    • Attach or detach remote devices


2 5 system programs

2.5 System Programs

  • Representative of O/S code that’s not in the kernel

  • Some items are interfaces to call system services

  • Some are distinct system programs or collections of programs


Chapter 2 operating system structures

  • Six categories (overlapping with previously presented lists)

    • File management

    • Status information

    • File modification

    • Programming language support (compilers, assemblers, interpreters, debuggers)

    • Program loading and execution (absolute loaders, relocatable loaders, linkers, etc.)

    • Communications


2 6 operating system design and implementation

2.6 Operating System Design and Implementation

  • Overview List:

    • Parameter 1: What kind of hardware?

    • Parameter 2: What kind of system?

    • Parameter 3: User requirements

    • Parameter 4: Developer requirements

    • Mechanisms and policies

    • Examples

    • O/S implementation


Chapter 2 operating system structures

  • Parameter one: What kind of hardware?

  • Parameter two: What kind of system?

    • Single user

    • Multi-user

    • Distributed

    • Real-time, etc.


Chapter 2 operating system structures

  • Parameter three: User requirements

    • Easy to learn, use, etc.

    • Fast, safe, reliable, etc.

    • Note that there is no obvious connection between these requirements and how you code the system in order to meet them

  • Parameter four: Developer requirements

    • Easy to design, implement, maintain, etc.


Chapter 2 operating system structures

  • Mechanisms and policies

  • Software design principle, separate the two

    • Policy = what to do

    • Mechanism = how to do it

  • In other words, don’t hardcode policy

  • Implement mechanisms that can enforce different policies depending on input parameters


Chapter 2 operating system structures

  • Examples

  • Unix

    • The micro-kernel can support batch, time-sharing, real-time, or any combination

    • What is supported depends on values in tables loaded at start-up

  • Windows takes the opposite approach

    • Mechanism and policy are tightly coupled

    • The system is relatively inflexible

    • There is a reason for this: It enforces the same look and feel across all installations


O s implementation

O/S implementation

  • Originally: assembly language

  • Modern systems

  • ~10% assembly language

    • Context switching

    • Possibly process scheduling

    • Possibly memory management

  • ~90% C—all remaining system functionality


2 7 operating system structure

2.7 Operating System Structure

  • Overview List:

    • Simple structure/no structure/monolithic

    • The layered approach

    • Modular design (object-oriented)


Chapter 2 operating system structures

  • Simple structure = not well structured

    • Simple systems that grew without a plan

    • Systems where immediate performance needs were paramount

    • Monolithic systems in general


Ms dos example

MS DOS example


Chapter 2 operating system structures

  • The left hand set of arrows represents a layered path through the software

  • The right-hand, non-layered path enabled performance, but made the system error-prone


Original unix example

Original Unix example


Chapter 2 operating system structures

  • The original Unix was no better

  • Superficially layered

  • The layers contained lots of stuff

  • Internally the layers were undisciplined in design


The layered approach

The Layered Approach


Chapter 2 operating system structures

  • Design functionality from the top down (from the outside in)

  • Code and debug from the bottom up (from the inside out)

  • Each layer has data structures, code, and interface

  • The implementation of the layers can change as long as the interface discipline is maintained

  • Somewhat object-oriented

  • Less general because each layer interacts with two neighbors only


Chapter 2 operating system structures

  • The fundamental challenge of layered systems is breaking it into layers and getting the dependencies straight

  • Each upper layer can only be implemented with calls to its lower neighbor

  • Sorting this out in the kernel is not trivial. Which is lowest, process scheduling, memory management, or some other function?

  • The practical disadvantage of layering is the performance cost of going down through the layers


Chapter 2 operating system structures

  • Microkernels contain the bare minimum of system code

    • Process management

    • Memory management

    • Message passing

  • The kernel remains small and fast and manageable by developers


Chapter 2 operating system structures

  • All other system code written into modules

    • Modules run like user applications

    • But they are privileged to make system calls

    • Communication between them is managed by the kernel

  • All other system programs can be changed without affecting the kernel


Modular design solaris

Modular Design (Solaris)


Object oriented design

Object-oriented design

  • Kernel and other modules can be dynamically loaded and linked to provide needed services

  • Different objects/modules can communicate with each other

  • Modern Unix systems take this approach


Mac os x

Mac OS X


Chapter 2 operating system structures

  • BSD = Berkeley Standard Distribution (kernel)

  • Mach = Carnegie Mellon (micro-kernel)

  • Different O/S functions are handled by the two

  • Mac OS X is a hybrid system


2 8 virtual machines

2.8 Virtual Machines

  • Logical conclusion of multi-user, multi-tasking

  • Logical conclusion of layering idea

  • Each user has access to a simulated hardware interface

  • Each user can load a different O/S, access different virtual peripherals, etc.


Chapter 2 operating system structures

  • The challenge in implementation is keeping track of real system mode vs. virtual user mode and real user mode vs. virtual user mode

  • With only one underlying machine there is only one real system mode, but there are many virtual system modes, one for each virtual machine

  • Sharing and communication between virtual machines is also an important challenge in implementation

  • A diagram follows


Benefits of virtual machines

Benefits of virtual machines

  • Users can run different O/S’s

  • Users are completely isolated from each other

  • System developers can work on O/S and other system code on one virtual machine while users run on the others

  • The original VM system—IBM mainframe—now configured to run Linux as well as CMS

  • VMware runs on Intel systems, making it possible to load >1 O/S on a system at a time


2 9 java

2.9 Java

  • Java has three parts

    • Programming language specification

    • Application programming interface (API)

    • Virtual machine specification

  • Note that Java is another example of a virtual machine architecture


Chapter 2 operating system structures

  • Programming language characteristics

    • Object-oriented

    • Architecture neutral

    • Distributed

    • Multi-threaded

    • Secure

    • With automatic garbage collection


Chapter 2 operating system structures

  • Java API editions

    • JSE = standard edition

      • Desktop applications and network applets

      • Graphics, I/O, security, db connectivity, networking

    • EE = enterprise edition

      • Server applications with db support

    • ME = micro edition

      • Applications on phones, pagers, handheld devices…


Chapter 2 operating system structures

  • The Java Virtual Machine = JVM

  • The Java platform =

    • An implementation of the JVM specification for any given hardware environment

    • Plus the Java API

  • The Java platform can be implemented

    • On top of a host O/S

    • In a browser

    • Or the JVM can be implemented in hardware


About the jvm

About the JVM

  • In a software environment, when main() is called in an application, this causes an instance of the JVM to be created

  • Each separate application or applet in execution has its own JVM

  • The JVM consists of a loader and an interpreter. The loader loads a .class file containing Java byte code

  • The interpreter, or just in time compiler, translates Java code into the commands and calls necessary in a given environment

  • Implementations of the JVM differ across environments, but not the specification


Running a java program

Running a Java Program


Random additional comments

Random additional comments

  • For development purposes a Java Development Environment would consist of a compiler plus a Java Runtime Environment (JRE)

  • In theory you might write an O/S with a microkernel in C/ASM and the rest in Java, using Java’s type safety mechanism for security. JX is an example

  • The MS .NET framework is similar to the Java approach


2 10 operating system debugging

2.10 Operating System Debugging

  • This section can be summarized as, “If you ever had to debug an operating system, it might be the hardest thing you ever had to do.”

  • Failure analysis and performance tuning are worthwhile concepts, but the details are unimportant

  • DTrace is of no particular consequence to us


Chapter 2 operating system structures

  • Kernighan’s Law appears here, and it’s memorable

  • “Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.”


Chapter 2 operating system structures

  • There are several worthwhile conclusions to draw from this:

  • 1. Strive for clarity and simplicity when code writing

  • Let an optimizing compiler do the cleverness part for you


Chapter 2 operating system structures

  • 2. Sometimes code is so incomprehensible that it’s easier to start from scratch than it is to debug it

  • 3. My take on commenting code:

  • You will start commenting code in earnest when the day comes that you have to fix code that you previously wrote and you no longer understand how it works


2 11 operating system generation

2.11 Operating System Generation

  • System generation = installing and setting up an O/S on a machine

  • Most O/S’s can function on multiple hardware platforms


Chapter 2 operating system structures

  • Installation requires setting parameters:

    • What CPU, how many, which instruction set(s)?

    • How much main memory?

    • What attached devices, type and model, numerical designation, interrupt number

    • O/S parameters: scheduling algorithm, number of I/O buffers, number of processes allowed, etc.


Chapter 2 operating system structures

  • Approaches to system generation fall into a range:

    • Set parameters in source, compile O/S, install

    • Select precompiled modules from libraries

    • Table driven—select options after O/S is up and running


Chapter 2 operating system structures

  • O/S performance parameters

    • Ease and speed of installation and set-up

    • Performance speed and memory size at run time

    • Ease of modification


Chapter 2 operating system structures

  • Ease of modification

    • Most systems probably have elements of both:

      • Major modifications: Change settings, recompile, reinstall

      • Minor modifications: Change settings from table options on the fly


2 12 system boot

2.12 System Boot

  • Already covered while going over chapter 1


The end

The End


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