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CHAPTER 3 OPERATING SYSTEM
STRUCTURE
OS Components
 OS Services
 OS API
 OS Apps
 OS Structures
 OS Generation

(for designer)
(for programmers)
(for application users)
OS COMPONENTS
Process management
 Memory management
 File management
 I/O management
 Secondary storage management
 Networking management
 Protection management
 Command-interpreter system

OS Components: Process management
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A process (进程) is a program in execution.
A process needs certain resources, including CPU
time, memory, files, and I/O devices, to accomplish
its task.
A process is an active (活动) entity whereas a
program is a passive (被动) entity.
OS process management activities:
 Process creation and deletion.
 process suspension and resumption.
 Process synchronization.
 Process communication.
 Process deadlock handling.
OS Components: Memory management
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Memory (内存) is a large array of words or bytes,
each with its own address.
Memory is a repository of quickly accessible data
shared by the CPU and I/O devices.
Main memory is a volatile storage device. It loses its
contents in the case of system failure.
OS memory management activities:
 Keep track of which parts of memory are used and
by whom.
 Decide which processes are to be loaded when
memory space becomes available.
 Allocate and deallocate memory space as needed.
OS Components: File management
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The OS provides a uniform logical view of information
storage. (Many different types of physical media.)
A file is a collection of related information defined by its
creator. File contents, file formats, file structures, file
attributes.
Files are organized into directories.
OS file management activities
 File creation and deletion.
 Directory creation and deletion.
 Support of primitives for manipulating files and
directories.
 Mapping files onto secondary storage.
 File backup on stable (nonvolatile) storage media.
OS Components: I/O management
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Too many I/O devices to mention.
The OS is designed to hide the peculiarities of
specific hardware devices from the user.
OS I/O management activities:
 A general device-driver interface.
 A memory-management component that includes
buffering, caching, and spooling.
 Drivers for specific hardware devices.
OS Components: Secondary-storage management
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Since main memory (primary storage,内存) is
volatile and too small to accommodate all data and
programs permanently, the computer system must
provide secondary storage （外存） to back up main
memory.
Most modern computer systems use disks as the
principle on-line storage medium, for both programs
and data.
The operating system is responsible for the following
activities in connection with disk management:
 Free space management,
 Storage allocation,
 Disk scheduling.
OS Components: Networking management
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Network:
 Computation speed-up,
 Increased data availability,
 Enhanced reliability,
 Communication (WWW, BBS),
OS networking management activities
 Network protocols (TCP/IP),
 Network device drivers (Physical layer and data
link layer).
OS Components: Protection management
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A computer system has multiple users and processes.
Protection refers to a mechanism for controlling access
by programs, processes, or users to both system and user
resources.
Protection mechanism must provide
 means for specification of the controls to be imposed,
 means for enforcement.
OS protection management activities:
 distinguish between authorized and unauthorized
usage.
 specify the controls to be imposed.
 provide a means of enforcement.
OS Components: Command-interpreter system
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Command-interpreter is the interface between the user
and the operating system. Character-based and GUIbased interpreters.
Command-interpreter can be used for both interactive
and batch users.
Many commands are given to the operating system by
control statements which deal with:
 Process creation and management,
 Main-memory management, file-system access,
 I/O handling, secondary-storage management,
 Networking,
 Protection.
OS SERVICES
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Program execution – system capability to load a program
into memory and to run it.
I/O operations – since user programs cannot execute I/O
operations directly, the operating system must provide
some means to perform I/O.
File-system manipulation – program capability to read,
write, create, and delete files.
Communications – exchange of information between
processes executing either on the same computer or on
different systems tied together by a network.
Implemented via shared memory or message passing.
Error detection – ensure correct computing by detecting
errors in the CPU and memory hardware, in I/O devices,
or in user programs.
OS Services (Additional )
• Resource allocation – allocating resources to multiple
•
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users or multiple jobs running at the same time.
Accounting – keeping track of and record which
users use how much and what kinds of computer
resources for account billing or for accumulating
usage statistics.
Protection – ensuring that all access to system
resources is controlled. A chain is only as strong as
its weakest link.
OS API (SYSTEM CALL)
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System calls provide the interface between a
running program and the operating system.

Generally available as assembly-language
instructions.

Languages defined to replace assembly language
for systems programming allow system calls to
be made directly (e.g., C, C++, Perl)
An example of using system class: copy file1 file2.
 How to provide file names,
 How to prepare files for input and output,
 How to enter the loop,
 How to release the resources.
OS API (System Call)

Three general methods are used to pass parameters
between a running program and the operating
system.

Pass parameters in registers.

Store the parameters in a table in memory, and
the table address is passed as a parameter in a
register. (linux) (see the next slide)

Push (store) the parameters onto the stack by the
program, and pop off the stack by operating
system.
OS API (System Call)
OS API: Types of system calls
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Process control
File management
Device management
Information maintenance
Communications
OS API: Process control
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Create and terminate processes: fork, exit.
Execute processes: exec.
Get/set process attributes.
Abort, end processes.
Wait for time, wait for event, signal event.
Allocate and free memory.
OS API: Process control (MS-DOS)
OS API: Process control (UNIX)
OS API: File management
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Create file, delete file.
Open, close.
Read, write, reposition.
Get/set file attributes.
Similar operations for directories.
OS API: Device management
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Request/release device.
Read, write, reposition.
Get/set device attributes.
Logically attach or detach devices.
OS API: Communication
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Create, delete communication connection.
Send, receive messages.
Transfer status information.
Attach or detach remote devices.
OS API: Communication
OS API: Information maintenance
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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.
OS SYSTEM PROGRAMS
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System programs provide a convenient environment
for program development and execution.
System programs:
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File manipulation; File modification.
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Status information.
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Programming language support; Program
loading and execution.

Communications.

Application programs.
System programs
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The most important system program: command
interpreter.
The command interpreter

can contain code segments,

or invoke utilities to execute commands.
Most users’ view of the operation system is defined
by system programs, not the actual system calls.
OS STRUCTURES
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Monolithic
（单层）
Structure
Layered
（分层）
Structure
Microkernel
（微内核） Structure
Virtual machine （虚拟机器）Structure
OS Structure: Monolithic structure

MS-DOS – written to provide the most
functionality in the least space.

not divided into modules.

Although MS-DOS has some structure, its
interfaces and levels of functionality are
not well separated.
OS Structure: Monolithic structure
OS Structure: Monolithic structure
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UNIX – limited by hardware functionality, the
original UNIX operating system had limited
structuring.
The original UNIX OS consists of two separable
parts: systems programs and the kernel.

The kernel consists of everything below the
system-call interface and above the physical
hardware.

The kernel provides the file system, CPU
scheduling, memory management, and other
operating-system functions; a large number of
functions for one level.
OS Structure: Monolithic structure
OS Structure: Layered structure
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The operating system is divided into a
number of layers (levels), each built on top
of lower layers. The bottom layer (layer 0),
is the hardware; the highest (layer N) is the
user interface.
With modularity, layers are selected such that
each uses functions (operations) and services
of only lower-level layers.
OS Structure: Layered structure
OS Structure: Layered structure (OS/2)
OS Structure: Microkernel structure
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Moves as much from the kernel into “user”
space.
Communication takes place between user
modules using message passing.
Benefits:
- easier to extend a microkernel,
- easier to port the operating system to new
architectures,
- more reliable (less code is running in kernel
mode),
- more secure.
OS Structure: Microkernel structure
Windows NT Client-Server Structure
VIRTUAL MACHINES
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A virtual machine takes the layered approach to its
logical conclusion. It treats hardware and the
operating system kernel as though they were all
hardware.
A virtual machine provides an interface identical to
the underlying bare hardware.
The operating system creates the illusion of multiple
processes, each executing on its own processor with
its own (virtual) memory.
Virtual Machines

The resources of the physical computer are shared to
create the virtual machines.
 CPU scheduling can create the appearance that
users have their own processor.
 Spooling and a file system can provide virtual card
readers and virtual line printers.
 A normal user time-sharing terminal serves as the
virtual machine operator’s console.
Virtual Machines: System models
Virtual Machines：Implementation
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Modes:
 virtual user mode and virtual monitor mode,
 Actual user mode and actual monitor mode
Time
 Whereas the real I/O might have taken 100
milliseconds, the virtual I/O might take less time
(because it is spooled) or more time (because it is
interpreted.)
 The CPU is being multi-programmed among many
virtual machines, further slowing down the virtual
machines in unpredictable ways.
Virtual Machines: Benefits
 Two advantages
 To provide a robust level of security
 no direct sharing of resources.
 Two solutions
 To allow system development to be done easily
 A perfect vehicle for OS research and
development.
 difficult to implement due to the effort
required to provide an exact duplicate to the
underlying machine.
 Wine for Linux.
Virtual Machines: JVM
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Compiled Java programs are platform-neutral
bytecodes executed by a Java Virtual Machine
(JVM).
JVM consists of
- class loader
- class verifier
- runtime interpreter
Just-In-Time (JIT) compilers increase performance
Virtual Machines: JVM
SYSTEM DESIGN, IMPLEMENTATION, AND
GENERATION

System design goals
 System type: batch, time shared, single user,
multi-user, distributed, real time, or general
purpose
 Two goals

User goals – operating system should be
convenient to use, easy to learn, reliable, safe,
and fast.

System goals – operating system should be
easy to design, implement, and maintain, as
well as flexible, reliable, error-free, and
efficient.
System design, implementation, and generation

Mechanisms and policies

Mechanisms determine how to do something,
policies decide what will be done.

The separation of policy from mechanism is a
very important principle, it allows maximum
flexibility if policy decisions are to be changed
later.
System design, implementation, and generation

System implementation

Traditionally written in assembly language,
operating systems can now be written in higherlevel languages.

Code written in a high-level language:

can be written faster.

is more compact.

is easier to understand and debug.

An operating system is far easier to port
(move to some other hardware) if it is written
in a high-level language.
System design, implementation, and generation
System generation

Operating systems are designed to run on any of a class
of machines; the system must be configured for each
specific computer site.

SYSGEN program obtains information concerning the
specific configuration of the hardware system. How to
use this system information

Recompiling,
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Relinking. (SCO, Linux)
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Table-driven. (Linux)

Booting – starting a computer by loading the kernel.
Bootstrap program – code stored in ROM that is able to
locate the kernel, load it into memory, and start its
execution.