SOLUTION MANUAL
OF
OPERATING SYSTEM
BY
Abraham Silberschatz,
Peter Baer Galvin & Greg Gagne
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios that require them to apply
statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of legal terminology and an ability to analyze facts within a legal framework. The focus is on how
well students understand the law and its application, rather than simply recalling legal rules. Additionally, many law exams involve essays where students must present well-argued opinions, critically
evaluate legal precedents, and suggest possible solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not
just about applying laws; it is also about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to reason ethically and consider the consequences
of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is
both an abstract and practical discipline. In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even social sciences are built. Thus, mathematics exams
serve to test not only a student’s computational ability but also their understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are designed to
test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of mathematics exams. Whether it's calculating the area of a geometrical shape,
solving algebraic equations, or analyzing a statistical dataset, the primary objective is to see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics,
exams often require students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for students who plan to pursue
careers in fields that rely heavily on mathematics, such as finance, physics,
, C P TER
Introduction
Practice Exercises
1.1 What are the three main purposes of an operating system?
Answer:
The three main puropses are:
• To provide an environment for a computer user to execute programs
on computer hardware in a convenient and efficient manner.
• To allocate the separate resources of the computer as needed to
solve the problem given. The allocation process should be as fair
and efficient as possible.
• As a control program it serves two major functions: (1) supervision
of the execution of user programs to prevent errors and improper use
of the computer, and (2) management of the operation and control
of I/O devices.
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios that require them to
apply statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of legal terminology and an ability to analyze
facts within a legal framework. The focus is on how well students understand the law and its application, rather than simply recalling legal rules.
Additionally, many law exams involve essays where students must present well-argued opinions, critically evaluate legal precedents, and suggest possible
solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not
just about applying laws; it is also about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to
reason ethically and consider the consequences of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing
problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and practical discipline. In many ways,
it is the foundation upon which fields like engineering, economics, computer science, and even social sciences are built. Thus, mathematics exams serve to test
not only a student’s computational ability but also their understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams
in mathematics are designed to test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of
mathematics exams. Whether it's calculating the area of a geometrical shape, solving algebraic equations, or analyzing a statistical dataset, the primary
objective is to see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics, exams often require
students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for
students who plan to pursue careers in fields that rely heavily on mathematics, such as finance, physics,
1.2 We have stressed the need for an operating system to make efficient use
of the computing hardware. When is it appropriate for the operating
system to forsake this principle and to “waste” resources? Why is such
a system not really wasteful?
Answer:
Single-user systems should maximize use of the system for the user. A
GUI might “waste” CPU cycles, but it optimizes the user’s interaction
with the system.
1.3 What is the main difficulty that a programmer must overcome in writing
an operating system for a real-time environment?
Answer:
The main difficulty is keeping the operating system within the fixed time
constraints of a real-time system. If the system does not complete a task
in a certain time frame, it may cause a breakdown of the entire system it
is running. Therefore when writing an operating system for a real-time
system, the writer must be sure that his scheduling schemes don’t allow
, response time to exceed the time constraint.
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based
scenarios that require them to apply statutes, case law, and legal principles to specific facts. These exams demand a
thorough understanding of legal terminology and an ability to analyze facts within a legal framework. The focus is on how
well students understand the law and its application, rather than simply recalling legal rules. Additionally, many law
exams involve essays where students must present well-argued opinions, critically evaluate legal precedents, and suggest
possible solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they
will face in practice. Legal practice is not just about applying laws; it is also about understanding the broader social and
ethical implications of decisions. Law exams often test a student's ability to reason ethically and consider the consequences
of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing problem-solving
and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and practical discipline.
In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even social
sciences are built. Thus, mathematics exams serve to test not only a student’s computational ability but also their
understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are
designed to test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at
the heart of mathematics exams. Whether it's calculating the area of a geometrical shape, solving algebraic equations, or
analyzing a statistical dataset, the primary objective is to see how well students can use mathematical tools to approach and
resolve problems. For higher-level mathematics, exams often require students to demonstrate the ability to prove theorems
or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for students who plan to
pursue careers in fields that rely heavily on mathematics, such as finance, physics,
2 Chapter 1 Introduction
1.4 Keeping in mind the various definitions of operating system, consider
whether the operating system should include applications such as Web
browsers and mail programs. Argue both that it should and that it should
not, and support your answers.
Answer:
An argument in favor of including popular applications with the
operating system is that if the application is embedded within the
operating system, it is likely to be better able to take advantage of
features in the kernel and therefore have performance advantages
over an application that runs outside of the kernel. Arguments against
embedding applications within the operating system typically dominate
however: (1) the applications are applications - and not part of an
operating system, (2) any performance benefits of running within the
kernel are offset by security vulnerabilities, (3) it leads to a bloated
operating system.
1.5 How does the distinction between kernel mode and user mode function
as a rudimentary form of protection (security) system?
Answer:
The distinction between kernel mode and user mode provides a rudi-
mentary form of protection in the following manner. Certain instructions
could be executed only when the CPU is in kernel mode. Similarly, hard-
ware devices could be accessed only when the program is executing in
kernel mode. Control over when interrupts could be enabled or disabled
is also possible only when the CPU is in kernel mode. Consequently, the
CPU has very limited capability when executing in user mode, thereby
enforcing protection of critical resources.
1.6 Which of the following instructions should be privileged?
a. Set value of timer.
b. Read the clock.
c. Clear memory.
d. Issue a trap instruction.
e. Turn off interrupts.
f. Modify entries in device-status table.
g. Switch from user to kernel mode.
h. Access I/O device.
Answer:
The following operations need to be privileged: Set value of timer, clear
, memory, turn off interrupts, modify entries in device-status table, access
I/O device. The rest can be performed in user mode.
1.7 Some early computers protected the operating system by placing it in
a memory partition that could not be modified by either the user job
or the operating system itself. Describe two difficulties that you think
could arise with such a scheme.
Answer:
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios
that require them to apply statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of
legal terminology and an ability to analyze facts within a legal framework. The focus is on how well students understand the law and
its application, rather than simply recalling legal rules. Additionally, many law exams involve essays where students must present
well-argued opinions, critically evaluate legal precedents, and suggest possible solutions to legal issues.Moreover, law exams prepare
students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not just about applying laws; it is also
about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to reason
ethically and consider the consequences of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while
also testing problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and
practical discipline. In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even
social sciences are built. Thus, mathematics exams serve to test not only a student’s computational ability but also their understanding
of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are designed to test a student’s
fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of mathematics exams. Whether
it's calculating the area of a geometrical shape, solving algebraic equations, or analyzing a statistical dataset, the primary objective is to
see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics, exams often require
students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical
thinking is essential for students who plan to pursue careers in fields that rely heavily on mathematics, such as finance, physics,
Practice Exercises 3
The data required by the operating system (passwords, access controls,
accounting information, and so on) would have to be stored in or passed
through unprotected memory and thus be accessible to unauthorized
users.
1.8 Some CPUs provide for more than two modes of operation. What are
two possible uses of these multiple modes?
Answer:
Although most systems only distinguish between user and kernel
modes, some CPUs have supported multiple modes. Multiple modes
could be used to provide a finer-grained security policy. For example,
rather than distinguishing between just user and kernel mode, you
could distinguish between different types of user mode. Perhaps users
belonging to the same group could execute each other’s code. The
machine would go into a specified mode when one of these users was
running code. When the machine was in this mode, a member of the
group could run code belonging to anyone else in the group.
Another possibility would be to provide different distinctions within
kernel code. For example, a specific mode could allow USB device drivers
to run. This would mean that USB devices could be serviced without
having to switch to kernel mode, thereby essentially allowing USB device
drivers to run in a quasi-user/kernel mode.
1.9 Timers could be used to compute the current time. Provide a short
description of how this could be accomplished.
Answer:
A program could use the following approach to compute the current
time using timer interrupts. The program could set a timer for some
time in the future and go to sleep. When it is awakened by the interrupt,
it could update its local state, which it is using to keep track of the
OF
OPERATING SYSTEM
BY
Abraham Silberschatz,
Peter Baer Galvin & Greg Gagne
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios that require them to apply
statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of legal terminology and an ability to analyze facts within a legal framework. The focus is on how
well students understand the law and its application, rather than simply recalling legal rules. Additionally, many law exams involve essays where students must present well-argued opinions, critically
evaluate legal precedents, and suggest possible solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not
just about applying laws; it is also about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to reason ethically and consider the consequences
of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is
both an abstract and practical discipline. In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even social sciences are built. Thus, mathematics exams
serve to test not only a student’s computational ability but also their understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are designed to
test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of mathematics exams. Whether it's calculating the area of a geometrical shape,
solving algebraic equations, or analyzing a statistical dataset, the primary objective is to see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics,
exams often require students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for students who plan to pursue
careers in fields that rely heavily on mathematics, such as finance, physics,
, C P TER
Introduction
Practice Exercises
1.1 What are the three main purposes of an operating system?
Answer:
The three main puropses are:
• To provide an environment for a computer user to execute programs
on computer hardware in a convenient and efficient manner.
• To allocate the separate resources of the computer as needed to
solve the problem given. The allocation process should be as fair
and efficient as possible.
• As a control program it serves two major functions: (1) supervision
of the execution of user programs to prevent errors and improper use
of the computer, and (2) management of the operation and control
of I/O devices.
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios that require them to
apply statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of legal terminology and an ability to analyze
facts within a legal framework. The focus is on how well students understand the law and its application, rather than simply recalling legal rules.
Additionally, many law exams involve essays where students must present well-argued opinions, critically evaluate legal precedents, and suggest possible
solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not
just about applying laws; it is also about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to
reason ethically and consider the consequences of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing
problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and practical discipline. In many ways,
it is the foundation upon which fields like engineering, economics, computer science, and even social sciences are built. Thus, mathematics exams serve to test
not only a student’s computational ability but also their understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams
in mathematics are designed to test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of
mathematics exams. Whether it's calculating the area of a geometrical shape, solving algebraic equations, or analyzing a statistical dataset, the primary
objective is to see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics, exams often require
students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for
students who plan to pursue careers in fields that rely heavily on mathematics, such as finance, physics,
1.2 We have stressed the need for an operating system to make efficient use
of the computing hardware. When is it appropriate for the operating
system to forsake this principle and to “waste” resources? Why is such
a system not really wasteful?
Answer:
Single-user systems should maximize use of the system for the user. A
GUI might “waste” CPU cycles, but it optimizes the user’s interaction
with the system.
1.3 What is the main difficulty that a programmer must overcome in writing
an operating system for a real-time environment?
Answer:
The main difficulty is keeping the operating system within the fixed time
constraints of a real-time system. If the system does not complete a task
in a certain time frame, it may cause a breakdown of the entire system it
is running. Therefore when writing an operating system for a real-time
system, the writer must be sure that his scheduling schemes don’t allow
, response time to exceed the time constraint.
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based
scenarios that require them to apply statutes, case law, and legal principles to specific facts. These exams demand a
thorough understanding of legal terminology and an ability to analyze facts within a legal framework. The focus is on how
well students understand the law and its application, rather than simply recalling legal rules. Additionally, many law
exams involve essays where students must present well-argued opinions, critically evaluate legal precedents, and suggest
possible solutions to legal issues.Moreover, law exams prepare students for the ethical dilemmas and moral questions they
will face in practice. Legal practice is not just about applying laws; it is also about understanding the broader social and
ethical implications of decisions. Law exams often test a student's ability to reason ethically and consider the consequences
of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while also testing problem-solving
and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and practical discipline.
In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even social
sciences are built. Thus, mathematics exams serve to test not only a student’s computational ability but also their
understanding of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are
designed to test a student’s fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at
the heart of mathematics exams. Whether it's calculating the area of a geometrical shape, solving algebraic equations, or
analyzing a statistical dataset, the primary objective is to see how well students can use mathematical tools to approach and
resolve problems. For higher-level mathematics, exams often require students to demonstrate the ability to prove theorems
or present formal mathematical arguments. This kind of rigorous, logical thinking is essential for students who plan to
pursue careers in fields that rely heavily on mathematics, such as finance, physics,
2 Chapter 1 Introduction
1.4 Keeping in mind the various definitions of operating system, consider
whether the operating system should include applications such as Web
browsers and mail programs. Argue both that it should and that it should
not, and support your answers.
Answer:
An argument in favor of including popular applications with the
operating system is that if the application is embedded within the
operating system, it is likely to be better able to take advantage of
features in the kernel and therefore have performance advantages
over an application that runs outside of the kernel. Arguments against
embedding applications within the operating system typically dominate
however: (1) the applications are applications - and not part of an
operating system, (2) any performance benefits of running within the
kernel are offset by security vulnerabilities, (3) it leads to a bloated
operating system.
1.5 How does the distinction between kernel mode and user mode function
as a rudimentary form of protection (security) system?
Answer:
The distinction between kernel mode and user mode provides a rudi-
mentary form of protection in the following manner. Certain instructions
could be executed only when the CPU is in kernel mode. Similarly, hard-
ware devices could be accessed only when the program is executing in
kernel mode. Control over when interrupts could be enabled or disabled
is also possible only when the CPU is in kernel mode. Consequently, the
CPU has very limited capability when executing in user mode, thereby
enforcing protection of critical resources.
1.6 Which of the following instructions should be privileged?
a. Set value of timer.
b. Read the clock.
c. Clear memory.
d. Issue a trap instruction.
e. Turn off interrupts.
f. Modify entries in device-status table.
g. Switch from user to kernel mode.
h. Access I/O device.
Answer:
The following operations need to be privileged: Set value of timer, clear
, memory, turn off interrupts, modify entries in device-status table, access
I/O device. The rest can be performed in user mode.
1.7 Some early computers protected the operating system by placing it in
a memory partition that could not be modified by either the user job
or the operating system itself. Describe two difficulties that you think
could arise with such a scheme.
Answer:
demonstrate legal reasoning and use the law to solve issues.In law exams, students are often presented with problem-based scenarios
that require them to apply statutes, case law, and legal principles to specific facts. These exams demand a thorough understanding of
legal terminology and an ability to analyze facts within a legal framework. The focus is on how well students understand the law and
its application, rather than simply recalling legal rules. Additionally, many law exams involve essays where students must present
well-argued opinions, critically evaluate legal precedents, and suggest possible solutions to legal issues.Moreover, law exams prepare
students for the ethical dilemmas and moral questions they will face in practice. Legal practice is not just about applying laws; it is also
about understanding the broader social and ethical implications of decisions. Law exams often test a student's ability to reason
ethically and consider the consequences of legal decisions on society.5.3. The Role of Mathematics ExamsMathematics exams, while
also testing problem-solving and logical reasoning, have a more defined and technical structure. Mathematics is both an abstract and
practical discipline. In many ways, it is the foundation upon which fields like engineering, economics, computer science, and even
social sciences are built. Thus, mathematics exams serve to test not only a student’s computational ability but also their understanding
of mathematical concepts and their ability to apply them in real-world contexts.Exams in mathematics are designed to test a student’s
fluency with numbers, algorithms, equations, and mathematical proofs. Problem-solving is at the heart of mathematics exams. Whether
it's calculating the area of a geometrical shape, solving algebraic equations, or analyzing a statistical dataset, the primary objective is to
see how well students can use mathematical tools to approach and resolve problems. For higher-level mathematics, exams often require
students to demonstrate the ability to prove theorems or present formal mathematical arguments. This kind of rigorous, logical
thinking is essential for students who plan to pursue careers in fields that rely heavily on mathematics, such as finance, physics,
Practice Exercises 3
The data required by the operating system (passwords, access controls,
accounting information, and so on) would have to be stored in or passed
through unprotected memory and thus be accessible to unauthorized
users.
1.8 Some CPUs provide for more than two modes of operation. What are
two possible uses of these multiple modes?
Answer:
Although most systems only distinguish between user and kernel
modes, some CPUs have supported multiple modes. Multiple modes
could be used to provide a finer-grained security policy. For example,
rather than distinguishing between just user and kernel mode, you
could distinguish between different types of user mode. Perhaps users
belonging to the same group could execute each other’s code. The
machine would go into a specified mode when one of these users was
running code. When the machine was in this mode, a member of the
group could run code belonging to anyone else in the group.
Another possibility would be to provide different distinctions within
kernel code. For example, a specific mode could allow USB device drivers
to run. This would mean that USB devices could be serviced without
having to switch to kernel mode, thereby essentially allowing USB device
drivers to run in a quasi-user/kernel mode.
1.9 Timers could be used to compute the current time. Provide a short
description of how this could be accomplished.
Answer:
A program could use the following approach to compute the current
time using timer interrupts. The program could set a timer for some
time in the future and go to sleep. When it is awakened by the interrupt,
it could update its local state, which it is using to keep track of the
