Operating System Concepts
Chapter 2 { Operating-System Structures
Based on the 9th Edition of:
Abraham Silberschatz, Peter B. Galvin and Jreg Gagne:. Operating System
Concepts
Department of Information Technology, College of Business, Law & Governance
OS Services OS-Interface System Calls System OS Design OS structure
Learning Objectives
To describe the services an operating system provides to
users, processes, and other systems
To discuss the various ways of structuring an operating system
To explain how operating systems are installed and
customized and how they boot
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Outline
1 Operating-System Services
2 User Operating-System Interface
3 System Calls
4 System Programs
5 Operating-System Design and Implementation
6 Operating-System Structure
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Operating-System Services
Operating systems provide an environment for execution of
programs and services to programs and users
One set of operating-system services provides functions that
are helpful to the user:
(a) User interface { Almost all operating systems have a user
interface (UI). Varies between Command-Line (CLI), Graphics
User Interface (GUI), Batch
(b) Program execution { The system must be able to load a
program into memory and to run that program, end execution,
either normally or abnormally (indicating error)
(c) I/O operations { A running program may require I/O, which
may involve a file or an I/O device
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Operating-System Services
(d) File-system manipulation { The file system is of particular
interest. Programs need to read and write files and
directories, create and delete them, search them, list file
information, permission management.
(e) Communications { Processes may exchange information, on
the same computer or between computers over a network.
Communications may be via shared memory or through
message passing (packets moved by the OS)
(f) Error detection { OS needs to be constantly aware of possible
errors. May occur in the CPU and memory hardware, in I/O
devices, in user program. For each type of error, OS should
take the appropriate action to ensure correct and consistent
computing. Debugging facilities can greatly enhance the
user’s and programmer’s abilities to efficiently use the system.
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Operating-System Services
Another set of OS functions exists for ensuring the efficient
operation of the system itself via resource sharing
(a’) Resource allocation { When multiple users or multiple jobs
running concurrently, resources (e.g., CPU cycles, main
memory, I/O devices) must be allocated to each of them.
(b’) Accounting { To keep track of which users use how much and
what kinds of computer resources
(c’) Protection and security { In a multiuser or networked
computer system, concurrent processes should not interfere
with each other
Protection involves ensuring that all access to system
resources is controlled
Security of the system from outsiders requires user
authentication, extends to defending external I/O devices
from invalid access attempts
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Operating-System Services
A view of operating-system services
user and other system programs
services
operating system
hardware
system calls
GUI batch
user interfaces
command line
program
execution
I/O
operations
file
systems communication allocation resource accounting
protection
and
security
error
detection
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User Operating-System Interface
Command-Line Interface (CLI) or Command Interpreter
Sometimes implemented in kernel, sometimes by systems
program
Sometimes multiple flavors implemented { shells
Primarily fetches a command from user and executes it
Sometimes commands built-in, sometimes just names of
programs. If the latter, adding new features doesn’t require
shell modification
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User Operating-System Interface
The Bourne shell command interpreter in Solaris 10
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User Operating-System Interface
Graphical User Interface (GUI)
Usually mouse, keyboard, and monitor
Icons represent files, programs, actions, etc
Various mouse buttons over objects in the interface cause
various actions (provide information, options, execute
function, open directory (known as a folder)
Invented at Xerox PARC
Many systems now include both CLI and GUI interfaces
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User Operating-System Interface
Graphical User Interface (GUI) {Cont.
Touchscreen devices require
new interfaces
Mouse not possible or not
desired
Actions and selection
based on gestures
Virtual keyboard for text
entry
Voice commands.
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User Operating-System Interface
Graphical User Interface (GUI) {Cont.
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Quick Quiz
1 A is an example of a systems program.
A. command interpreter
B. Web browser
C. text formatter
D. database system
Answer:
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Quick Quiz
1 A is an example of a systems program.
A. command interpreter
B. Web browser
C. text formatter
D. database system
Answer: A
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Quick Quiz
1 A is an example of a systems program.
A. command interpreter
B. Web browser
C. text formatter
D. database system
Answer: A
2 Which of the following statements is incorrect?
A. An operating system provides an environment for the execution
of programs.
B. An operating system manages system resources.
C. Operating systems provide both command line as well as
graphical user interfaces.
D. Operating systems must provide both protection and security.
Answer:
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Quick Quiz
1 A is an example of a systems program.
A. command interpreter
B. Web browser
C. text formatter
D. database system
Answer: A
2 Which of the following statements is incorrect?
A. An operating system provides an environment for the execution
of programs.
B. An operating system manages system resources.
C. Operating systems provide both command line as well as
graphical user interfaces.
D. Operating systems must provide both protection and security.
Answer: C
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System Calls
Programming interface to the services provided by the OS
Typically written in a high-level language (C or C++)
Mostly accessed by programs via a high-level Application
Programming Interface (API) rather than direct system call
use
Three most common APIs are Win32 API for Windows,
POSIX API for POSIX-based systems (including virtually all
versions of UNIX, Linux, and Mac OS X), and Java API for
the Java virtual machine (JVM)
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System Calls
System call sequence to copy the contents of one file to another file
source file destination file
Example System Call Sequence
Acquire input file name
Write prompt to screen
Accept input
Acquire output file name
Write prompt to screen
Accept input
Open the input file
if file doesn’t exist, abort
Create output file
if file exists, abort
Loop
Read from input file
Write to output file
Until read fails
Close output file
Write completion message to screen
Terminate normally
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System Calls
System Call Implementation
Typically, a number associated with each system call
System-call interface maintains a table indexed according to
these numbers
The system call interface invokes the intended system call in
OS kernel and returns status of the system call and any return
values
The caller need know nothing about how the system call is
implemented. Just needs to obey API and understand what
OS will do as a result call. Most details of OS interface
hidden from programmer by API.
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System Calls
The handling of a user application invoking the open() system call
Implementation
of open ( )
system call
open ( )
user
mode
return
user application
system call interface
kernel
mode
i
open ( )
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System Calls { Parameter Passing
Three general methods used to pass parameters to the OS
1 Pass the parameters in registers {in some cases, may be more
parameters than registers
2 Parameters stored in a block, or table, in memory, and address
of block passed as a parameter in a register. This approach
taken by Linux and Solaris
3 Parameters placed, or pushed, onto the stack by the program
and popped off the stack by the operating system
Block and stack methods do not limit the number or length of
parameters being passed
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System Calls { Parameter Passing
Passing of parameters as a table
code for
system
call 13
operating system
user program
use parameters
from table X
register
X
X: parameters
for call
load address X
system call 13
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Types of System Calls
Process control (e.g., create, terminate, end, abort, etc.)
File management (e.g., create, delete, open, close, read, write,
etc.)
Device management (e.g., request device, release device, read,
write, reposition, etc.)
Information maintenance (e.g., get time/date, set time/date,
get/set system data, etc.)
Communications (i.e., create/delete communication
connection, send/receive messages, etc.)
Protection (get/set permissions, allow/deny user access, etc.)
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Types of System Calls
Examples of
Windows and Unix
System Calls
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Types of System Calls
Standard C library
handling of
write ()
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Types of System Calls
MS-DOS execution. (a) At system startup. (b) Running a program
(a) (b)
free memory
command
interpreter
kernel
process
free memory
command
interpreter
kernel
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 24
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer: B
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer: B
2 True or False { System calls can be run in either user mode
or kernel mode.
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 24
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer: B
2 True or False { System calls can be run in either user mode
or kernel mode.
Answer: False
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer: B
2 True or False { System calls can be run in either user mode
or kernel mode.
Answer: False
3 True or False { Application programmers typically use an
API rather than directly invoking system calls.
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 24
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Quick Quiz
1 provide(s) an interface to the services provided by an
operating system.
A. Shared memory
B. System calls
C. Simulators
D. Communication
Answer: B
2 True or False { System calls can be run in either user mode
or kernel mode.
Answer: False
3 True or False { Application programmers typically use an
API rather than directly invoking system calls.
Answer: True
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System Programs
System programs provide a convenient environment for program
development and execution. They can be divided into:
File manipulation (Create, delete, copy, print, …)
Status information sometimes stored in a File modification
(date, time, disk space, number of users, …)
Programming language support (compilers, assemblers, …)
Program loading and execution (absolute/relocatable loader,
linkage editors, debugging systems,…)
Communications (among processes, users, and computer
systems)
Background services (startup, terminate, …)
Application programs (Not typically considered part of OS)
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Operating-System Design and Implementation
Design and Implementation of OS not “solvable”, but some
approaches have proven successful
Internal structure of different OS can vary widely
Start the design by defining goals and specifications
Affected by choice of hardware, type of system
User goals and System 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
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Operating-System Design and Implementation
Important principle to separate
Policy: What will be done?
Mechanism: How to do it?
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 (example timer)
Specifying and designing an OS is highly creative task of
software engineering
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Operating-System Design and Implementation
Implementation
Much variation
Early Operating Systems in assembly language; now in C,
C++
Actually usually a mix of languages; lowest levels in assembly;
main body in C
Systems programs in C, C++, scripting languages like PERL,
Python, shell scripts
More high-level language easier to port to other hardware
{but slower
Emulation can allow an OS to run on non-native hardware
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer:
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer: B
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer: B
2 True or False { In general, Windows system calls have
longer, more descriptive names and UNIX system calls use
shorter, less descriptive names.
Answer:
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer: B
2 True or False { In general, Windows system calls have
longer, more descriptive names and UNIX system calls use
shorter, less descriptive names.
Answer: True
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer: B
2 True or False { In general, Windows system calls have
longer, more descriptive names and UNIX system calls use
shorter, less descriptive names.
Answer: True
3 True or False { Many operating system merge I/O devices
and files into a combined file because of the similarity of
system calls for each.
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 29
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Quick Quiz
1 Policy .
A. determines how to do something
B. determines what will be done
C. is not likely to change across places
D. is not likely to change over time
Answer: B
2 True or False { In general, Windows system calls have
longer, more descriptive names and UNIX system calls use
shorter, less descriptive names.
Answer: True
3 True or False { Many operating system merge I/O devices
and files into a combined file because of the similarity of
system calls for each.
Answer: True
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Operating-System Structure
General-purpose OS is very large program
Various ways to structure ones
Simple structure { MS-DOS
More complex { UNIX
Layered { an abstraction
Microkernel { Mach (developed in Carnegie Mellon University)
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Operating-System 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 ROM BIOS device drivers
application program
MS-DOS device drivers
resident system program
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Operating-System Structure
UNIX
Limited by hardware functionality, the original UNIX operating
system had limited structuring. The UNIX OS consists of two
separable parts:
1 Systems programs
2 The kernel
Consists of everything below the system-call interface and
above the physical hardware
Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a large
number of functions for one level
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Operating-System Structure
Traditional UNIX system structure
kernel
(the users)
shells and commands
compilers and interpreters
system libraries
system-call interface to the kernel
signals terminal
handling
character I/O system
terminal drivers
file system
swapping block I/O
system
disk and tape drivers
CPU scheduling
page replacement
demand paging
virtual memory
kernel interface to the hardware
terminal controllers
terminals
device controllers
disks and tapes
memory controllers
physical memory
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Operating-System Structure
Layered Approach
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
layer N
user interface
•••
layer 1
layer 0
hardware
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Operating-System Structure
Microkernels
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
Detriments { Performance overhead of user space to kernel
space communication
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Operating-System Structure
Microkernel system structure
Application
Program
File
System
Device
Driver
Interprocess
Communication
memory
managment
CPU
scheduling
messages messages
microkernel
hardware
user
mode
kernel
mode
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Operating-System Structure
Modules
Many modern operating systems implement loadable kernel
modules
Uses object-oriented approach
Each core component is separate
Each talks to the others over known interfaces
Each is loadable as needed within the kernel
Overall, similar to layers but with more flexible
Linux, Solaris, etc
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Operating-System Structure
Solaris modular approach
core Solaris
kernel
file systems
loadable
system calls
executable
formats
STREAMS
modules
miscellaneous
modules
device and
bus drivers
scheduling
classes
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Operating-System Structure
Hybrid Systems
Most modern operating systems are actually not one pure
model
Hybrid combines multiple approaches to address performance,
security, usability needs
Linux and Solaris kernels in kernel address space, so
monolithic, plus modular for dynamic loading of functionality
Windows mostly monolithic, plus microkernel for different
subsystem personalities
Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa
programming environment
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Operating-System Structure
Mach microkernel and BSD Unix parts, plus I/O kit and
dynamically loadable modules (called kernel extensions)
graphical user interface
Aqua
application environments and services
kernel environment
Java Cocoa Quicktime BSD
Mach
I/O kit kernel extensions
BSD
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Operating-System Structure
iOS
Apple mobile OS for iPhone, iPad
Structured on Mac OS X, added functionality
Does not run OS X applications natively {also
runs on different CPU architecture (ARM vs.
Intel)
Cocoa Touch Objective-C API for developing
apps
Media services layer for graphics, audio, video
Core services provides cloud computing,
databases
Core operating system, based on Mac OS X
kernel
Cocoa Touch
Media Services
Core Services
Core OS
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Operating-System Structure
Android
Developed by Open Handset Alliance (mostly Google) {Open
Source
Similar stack to IOS
Based on Linux kernel but modified {provides process,
memory, device-driver management
Runtime environment includes core set of libraries and Dalvik
virtual machine
Apps developed in Java plus Android API {Java class files
compiled to Java bytecode then translated to executable than
runs in Dalvik VM
Libraries include frameworks for web browser (webkit),
database (SQLite), multimedia, smaller libc
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Operating-System Structure
Android architecture
Applications
Application Framework
Android runtime
Core Libraries
Dalvik
virtual machine
Libraries
Linux kernel
SQLite openGL
surface
manager
webkit libc
media
framework
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Operating-System Debugging
Debugging is finding and fixing errors, or bugs
OS generate log files containing error information
Failure of an application can generate core dump file
capturing memory of the process
Operating system failure can generate crash dump file
containing kernel memory
Beyond crashes, performance tuning can optimize system
performance
Sometimes using trace listings of activities, recorded for
analysis
Profiling is periodic sampling of instruction pointer to look for
statistical trends
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Operating-System Debugging
Performance Tuning
Improve performance
by removing
bottlenecks
OS must provide
means of computing
and displaying
measures of system
behavior. For
example, “top”
program or Windows
Task Manager
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Operating-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
Used to build system-specific compiled kernel or system-tuned
Can general more efficient code than one general kernel
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System Boot
When power initialized on system, execution starts at a fixed
memory location {firmware ROM used to hold initial boot
code
Operating system must be made available to hardware so
hardware can start it
Small piece of code { bootstrap loader, stored in ROM or
EEPROM locates the kernel, loads it into memory, and starts
it
Sometimes two-step process where boot block at fixed location
loaded by ROM code, which loads bootstrap loader from disk
Common bootstrap loader, GRUB, allows selection of kernel
from multiple disks, versions, kernel options
Kernel loads and system is then running
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Quick Quiz
1 If a program terminates abnormally, a dump of memory may
be examined by a to determine the cause of the
problem.
A. module
B. debugger
C. shell
D. control card
Answer:
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Quick Quiz
1 If a program terminates abnormally, a dump of memory may
be examined by a to determine the cause of the
problem.
A. module
B. debugger
C. shell
D. control card
Answer: B
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Quick Quiz
1 If a program terminates abnormally, a dump of memory may
be examined by a to determine the cause of the
problem.
A. module
B. debugger
C. shell
D. control card
Answer: B
2 The major difficulty in designing a layered operating system
approach is .
A. appropriately defining the various layers
B. making sure that each layer hides certain data structures,
hardware, and operations from higher-level layers
C. debugging a particular layer
D. making sure each layer is easily converted to modules
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 48
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Quick Quiz
1 If a program terminates abnormally, a dump of memory may
be examined by a to determine the cause of the
problem.
A. module
B. debugger
C. shell
D. control card
Answer: B
2 The major difficulty in designing a layered operating system
approach is .
A. appropriately defining the various layers
B. making sure that each layer hides certain data structures,
hardware, and operations from higher-level layers
C. debugging a particular layer
D. making sure each layer is easily converted to modules
Answer: A
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Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 49
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Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer: A
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Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer: A
2 True or False { An initial bootstrap program is in the form
of random-access memory (RAM).
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 49
OS Services OS-Interface System Calls System OS Design OS structure
Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer: A
2 True or False { An initial bootstrap program is in the form
of random-access memory (RAM).
Answer: False
Chapter 2 { Operating-System Structures Operating System Concepts 49
OS Services OS-Interface System Calls System OS Design OS structure
Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer: A
2 True or False { An initial bootstrap program is in the form
of random-access memory (RAM).
Answer: False
3 True or False { Mac OS X is a hybrid system consisting of
both the Mach microkernel and BSD UNIX.
Answer:
Chapter 2 { Operating-System Structures Operating System Concepts 49
OS Services OS-Interface System Calls System OS Design OS structure
Quick Quiz
1 A boot block .
A. typically only knows the location and length of the rest of the
bootstrap program
B. typically is sophisticated enough to load the operating system
and begin its execution
C. is composed of multiple disk blocks
D. is composed of multiple disk cylinders
Answer: A
2 True or False { An initial bootstrap program is in the form
of random-access memory (RAM).
Answer: False
3 True or False { Mac OS X is a hybrid system consisting of
both the Mach microkernel and BSD UNIX.
Answer: True
Chapter 2 { Operating-System Structures Operating System Concepts 49
OS Services OS-Interface System Calls System OS Design OS structure
End of Chapter 2
Chapter 2 { Operating-System Structures Operating System Concepts 50