Operating-System Structures

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Chapter 2 System Structures

Operating-System Structures

Goals: Provide a way to understand an operating systems

Services

Interface

System Components

The type of system desired is the

basis for choices among various

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Operation-System Services

Goal:

Provide an environment for the execution of programs.

Services are provided to programs and their users.

User Interface (UI)

Command Line Interface, Batch Interface, Graphical User Interface (GUI), etc.

Interface between the user and the operating system

Operation-System Services

Friendly UI’s

Command-line-based interfaces or mused-based window-and-menu interface

e.g., UNIX shell and command.com in MS-DOS

Program Execution

Loading, running, terminating, etc

Get the next command Execute the command User-friendly?

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Operation-System Services

I/O Operations

General/special operations for devices:

Efficiency & protection

File-System Manipulation

Read, write, create, delete, etc.

Files and Directories

Permission Management

Communications

Intra-processor or inter-processor communication – shared memory or message passing

Operation-System Services

Error Detection

Possible errors from CPU, memory, devices, user programs Æ Ensure correct & consistent computing

Resource Allocation

 Utilization & efficiency

Accounting

 Statistics or Accounting

Protection & Security

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User OS Interface – Command Interpreter

Two approaches:

Contain codes to execute commands

Fast but the interpreter tends to be big!

Painful in revision!

del cd

User OS Interface – Command Interpreter

Implement commands as system programs Æ Search exec files which corresponds to commands (UNIX)

Issues

a. Parameter Passing

Potential Hazard: virtual memory b. Being Slow

c. Inconsistent Interpretation of Parameters

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User OS Interface – GUI

Components

Screen, Icons, Folders, Pointer, etc.

History

Xerox PARC research facility (1970’s)

Mouse – 1968

Mac OS – 1980’s

Windows 1.0 ~ XP

User OS Interface – GUI

Unix & Linux

Common Desktop Environment (CDE), X-Windows, K Desktop Environment (KDE), GNOME

Trend

Mixture of GUI and command-line interfaces

Multimedia, Intelligence, etc.

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System Calls

System calls

Interface between processes & OS

How to make system calls?

Assemble-language instructions or subroutine/functions calls in high-level language such as C or Perl?

Generation of in-line instructions or a call to a special run-time routine.

Example: read and copy of a file!

Library Calls vs System Calls

System Calls

Application Programming Interface (API)

Examples: Win 32 API for Windows, POSIX API for POSIX-based

Systems, Java API for Java virtual machines

Benefits (API vs System Calls)

Portability

Ease of Use & Better Functionality

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System Calls

How a system call occurs?

Types and information

Parameter Passing

Registers

Registers pointing to blocks

Linux

Stacks

x: parameters for call load address x system call 13

x

register

use parameters from table x

Code for System Call 13

System Calls

Process Control

File Management

Device Management

Information Maintenance

Communications

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System Calls

Process & Job Control

End (normal exit) or abort (abnormal)

Error level or no

Interactive, batch, GUI-supported systems

Load and execute

How to return control?

e.g., shell load & execute commands

Creation and/or termination of processes

Multiprogramming?

System Calls

Process & Job Control (continued)

Process Control

Get or set attributes of processes

Wait for a specified amount of time or an event

Signal event

Memory dumping, profiling, tracing, memory allocation & de-allocation

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System Calls

Examples: MS-DOS & UNIX

kernel command interpreter process free memory

kernel interpreter

process B free memory

process A

System Calls

File Management

Create and delete

Open and close

Read, write, and reposition (e.g., rewinding)

lseek

Get or set attributes of files

Operations for directories

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System Calls

Device management

Physical or virtual devices, e.g., files.

Request or release

Open and close of special files

Files are abstract or virtual devices.

Read, write, and reposition (e.g., rewinding)

Get or set file attributes

Logically attach or detach devices

System Calls

Information maintenance

Get or set date or time

Get or set system data, such as the amount of free memory

Communication

Message Passing

Open, close, accept connections

Host ID or process ID

Send and receive messages

Transfer status information

Shared Memory

Memory mapping & process synchronization

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System Calls

Shared Memory

Max Speed & Comm Convenience

Message Passing

No Access Conflict & Easy Implementation

kernel Process A Process B

Shared Memory

M M M

System Programs

Goal:

Provide a convenient environment for program development and execution

Types

File Management, e.g., rm.

Status information, e.g., date.

File Modifications, e.g., editors.

Program Loading and Executions, e.g., loader.

Programming Language Supports, e.g.,

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System Design &

Implementation

Design Goals & Specifications:

User Goals, e.g., ease of use

System Goals, e.g., reliable

Rule 1: Separation of Policy & Mechanism

Policy：What will be done?

Mechanism：How to do things?

Example: timer construct and time slice

Two extreme cases:

Microkernel-based OS Macintosh OS

System Design &

Implementation

OS Implementation in High-Level Languages

E.g., UNIX, OS/2, MS NT, etc.

Advantages:

Being easy to understand & debug

Being written fast, more compact, and portable

Disadvantages:

Less efficient but more storage for code

* Tracing for bottleneck identification, exploring of excellent algorithms, etc.

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OS Structure – MS-DOS

MS-DOS Layer Structure

Application program

Resident system program

MS-DOS device drivers

ROM BIOS device drivers

OS Structure – UNIX

terminal controller, terminals,

physical memory, device controller, devices such as disks, memory, etc.

CPU scheduling, signal handling, virtual memory, paging, swapping,

file system, disk drivers, caching/buffering, etc.

Shells, compilers, X, application programs, etc.

Kernel interface to the hardware System call interface

useruser user useruser user User user

interface

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OS Structure

A Layered Approach – A Myth

Advantage: Modularity ~ Debugging &

Verification

Difficulty: Appropriate layer definitions, less efficiency due to overheads！

Layer M Layer M-1

hidden ops new

ops

existing ops

OS Structure

A Layer Definition Example:

L5 User programs L4 I/O buffering

L3 Operator-console device driver L2 Memory management

L1 CPU scheduling

L0 Hardware

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OS Structure – OS/2

OS/2 Layer Structure

Application Application Application

Subsystem Subsystem Subsystem

Device driver Device driver Device driver Application-program Interface

‧memory management

System kernel ‧task scheduling

‧device management

* Some layers of NT were from user space to kernel space in NT4.0

OS Structure – Microkernels

The concept of microkernels was

proposed in CMU in mid 1980s (Mach).

Moving all nonessential components from the kernel to the user or system programs!

No consensus on services in kernel

Mostly on process and memory management and communication

Benefits:

Ease of OS service extensions Æ

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OS Structure – Microkernels

Examples

Microkernels: True64UNIX (Mach kernel), MacOS X (Mach kernel), QNX (msg passing, proc scheduling, HW interrupts, low-level networking)

Hybrid structures: Windows NT

kernel

OS/2

Applications OS/2 Server

POSIX

Applications POSIX Server Win32

Applications Win32 Server

OS Structure – Modules

A Modular Kernel

A Set of Core Components

Dynamic Loadable Modules

E.g., Solaris: Scheduling Classes, File Systems, Loadable System Calls, Executable Formats, STREAMS Modules, Miscellaneous, Device and Bus Drivers

Characteristics:

Layer-Like – Modules

Microkernel-Like – the Primary Module

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OS Structure – Modules

Example Mac OS X

Application Environments and Common Services

BSD: Command Line Interface, Support for Networking and File Systems, an

Implementation of POSIX APIs.

Mach: Memory Management, Support for Remote Procedure Calls, Interprocess Communication Facilities

The Kernel Environment: I/O Kit for the Development of Device Drivers and Dynamically Loadable Modules.

Kernel Environment BSD

Mach App. Environ. &

Common Services

Virtual Machine

Virtual Machines: provide an interface that is identical to the underlying bare hardware

interface

processes processes processes processes

kernel kernel kernel kernel

VM1 VM2 VM3

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Virtual Machine

Implementation Issues:

Emulation of Physical Devices

E.g., Disk Systems

An IBM minidisk approach

User/Monitor Modes

(Physical) Monitor Mode

Virtual machine software

(Physical) User Mode

Virtual monitor mode & Virtual user mode

Virtual Machine

virtual user mode virtual monitor mode monitor mode

processes processes processes

kernel 1 kernel 2 kernel 3

virtual machine software hardware

P1/VM1 system call

Trap

Service for the system call

Set program counter

& register contents,

& then restart VM1

Simulate the effect of the I/O instruction

Restart VM1 Finish

service

time

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Virtual Machine

Disadvantages:

Slow!

Execute most instructions directly on the hardware

No direct sharing of resources

Physical devices and communications

* I/O could be slow (interpreted) or fast (spooling)

Virtual Machine

Advantages:

Complete Protection – Complete Isolation！

OS Research & Development

System Development Time

Extensions to Multiple Personalities, such as Mach (software emulation)

Emulations of Machines and OS’s, e.g., Windows over Linux

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Virtual Machine – VMware

VMware – The visualization layer abstracts the physical hardware into isolated virtual

machines running as guest operating systems.

CPU memory I/O devices

Linux/Windows

Guest OS (Windows NT) Virtual OS Virtual memory

Virtual devices applications

Guest OS (free BSD) Virtual OS Virtual memory

Virtual devices applications applications

visualization layer

Virtual Machine – Java

Sun Microsystems in late 1995

Java Language and API Library

Java Virtual Machine (JVM)

Class loader (for bytecode .class files)

Class verifier

Java interpreter

An interpreter, a just-in-time (JIT) compiler, hardware

class loader verifier java interpreter

host system

java .class files

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Virtual Machine – Java

JVM

Garbage collection

Reclaim unused objects

Implementation being specific for different systems

Programs are architecture neutral and portable

class loader verifier java interpreter

host system

java .class files

System Generation

SYSGEN (System Generation)

Ask and probe for information concerning the specific configuration of a hardware system

CPU, memory, device, OS options, etc.

No recompilation Recompilation

& completely Linking of of a modified table-driven modules for source code

selected OS

Issues

Size, Generality, Ease of modification

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System Boot

Booting

The procedure of starting a computer by loading the kernel.

The bootstrap program or the bootstrap loader

Firmware being ROM or EEPROM resident

Boot/system disk with a boot block

Operating-System Structures

Chapter 2

System Structures