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COS3721 Exam Questions And Answers
100% Verified And Updated.
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✔a) If the operating system
cannot modify the memory, then some important and critical data such as protection and/or
security data (e.g. passwords and access control information) necessary for the operating system
would have to be passed through or stored in unprotected memory slots and would be accessible
to unauthorised users.
b) The operating system could never be updated or patched, since it is not modifiable or
accessible by the user or the operating system itself.
Distinguish between the client-server and peer-to-peer models of Distributed systems. -
Answer✔The core benefits of Peer-to-Peer model (in opposition with the centralized model)
stem from the fact that each participating computer in the model can be both the client and
server.
In a Peer-to-peer model, services are distributed across a collection of peers, rather than having a
single, centralized server. Peer-to-peer provides fault tolerance and redundancy. Also, because
peers constantly migrate, they can provide a level of security over a server that always exists at a
known location on the Internet. Peer-to-peer systems can also potentially provide higher network
bandwidth because you can collectively use all the bandwidth of peers, rather than the single
bandwidth that is available to a single server.
In a multiprogramming and time-sharing environment, several users share the system
simultaneously. This situation can result in various security problems.
What are two such problems? - Answer✔Stealing or copying one's programs or data; using
system resources (CPU, memory, disk space, peripherals) without proper accounting.
Can we ensure the same degree of security in a time-shared machine as in a dedicated machine?
Explain your answer. - Answer✔Probably not, since a human, and the more complex can
inevitably break any protection scheme devised by humans the scheme, the more difficult it is to
feel confident of its correct implementation.
What is the purpose of interrupts? How does an interrupt differ from a trap? Can traps be
generated intentionally by a user program? If so, for what purpose? - Answer✔An interrupt is a
1|Page
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hardware-generated change of flow within the system. An interrupt handler is summoned to deal
with the cause of the interrupt; control is then returned to the interrupted context and instruction.
A trap is a software-generated interrupt. An interrupt can be used to signal the completion of an
I/O to obviate the need for device polling. A trap can be used to call operating system routines or
to catch arithmetic errors.
Describe some of the challenges of designing operating systems for mobile devices compared
with designing operating systems for traditional PCs. - Answer✔The greatest challenges in
designing mobile operating systems include:
Less storage capacity means the operating system must manage memory carefully.
The operating system must also manage power consumption carefully.
Less processing power plus fewer processors mean the operating system must carefully
apportion processors to applications.
Identify several advantages and several disadvantages of open-source operating systems. Include
the types of people who would find each aspect to be an advantage or a disadvantage. -
Answer✔Open source operating systems have the advantages of having many people working on
them, many people debugging them, ease of access and distribution, and rapid update cycles.
Further, for students and programmers, there is certainly an advantage to being able to view and
modify the source code. Typically open source operating systems are free for some forms of use,
usually just requiring payment for support services. Commercial operating system companies
usually do not like the competition that open source
operating systems bring because these features are difficult to compete against. Some open
source operating systems do not offer paid support programs. Some companies avoid open
source projects because they need paid support, so that they have some entity to hold accountable
if there is a problem or they need help fixing an issue. Finally, some complain that a lack of
discipline in the coding of open source operating systems means that backward compatibility is
lacking making upgrade
What role do device controllers and device drivers play in a computer system? - Answer✔A
device controller provides for an interface between the peripheral(s) that it controls and the
operating system. It collaborates with the device driver, by means of interrupt, special-purpose
registers and when necessary Direct Memory Access (DMA), to transfer data from/to the
peripheral(s) to/from the buffer storage.
A device driver on the other side understands the device controller and hence provides the rest of
the operating system with a uniform interface to de device.
Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU's
execution load.
How does the CPU interface with the device to coordinate the transfer? - Answer✔The CPU can
initiate a DMA operation by writing values into special registers that can be independently
accessed by the device. The device initiates the corresponding operation once it receives a
command from the CPU.
2|Page
COS3721 Exam Questions And Answers
100% Verified And Updated.
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✔a) If the operating system
cannot modify the memory, then some important and critical data such as protection and/or
security data (e.g. passwords and access control information) necessary for the operating system
would have to be passed through or stored in unprotected memory slots and would be accessible
to unauthorised users.
b) The operating system could never be updated or patched, since it is not modifiable or
accessible by the user or the operating system itself.
Distinguish between the client-server and peer-to-peer models of Distributed systems. -
Answer✔The core benefits of Peer-to-Peer model (in opposition with the centralized model)
stem from the fact that each participating computer in the model can be both the client and
server.
In a Peer-to-peer model, services are distributed across a collection of peers, rather than having a
single, centralized server. Peer-to-peer provides fault tolerance and redundancy. Also, because
peers constantly migrate, they can provide a level of security over a server that always exists at a
known location on the Internet. Peer-to-peer systems can also potentially provide higher network
bandwidth because you can collectively use all the bandwidth of peers, rather than the single
bandwidth that is available to a single server.
In a multiprogramming and time-sharing environment, several users share the system
simultaneously. This situation can result in various security problems.
What are two such problems? - Answer✔Stealing or copying one's programs or data; using
system resources (CPU, memory, disk space, peripherals) without proper accounting.
Can we ensure the same degree of security in a time-shared machine as in a dedicated machine?
Explain your answer. - Answer✔Probably not, since a human, and the more complex can
inevitably break any protection scheme devised by humans the scheme, the more difficult it is to
feel confident of its correct implementation.
What is the purpose of interrupts? How does an interrupt differ from a trap? Can traps be
generated intentionally by a user program? If so, for what purpose? - Answer✔An interrupt is a
1|Page
, ©FYNDLAY 2024/2025 ALL RIGHTS RESERVED.
hardware-generated change of flow within the system. An interrupt handler is summoned to deal
with the cause of the interrupt; control is then returned to the interrupted context and instruction.
A trap is a software-generated interrupt. An interrupt can be used to signal the completion of an
I/O to obviate the need for device polling. A trap can be used to call operating system routines or
to catch arithmetic errors.
Describe some of the challenges of designing operating systems for mobile devices compared
with designing operating systems for traditional PCs. - Answer✔The greatest challenges in
designing mobile operating systems include:
Less storage capacity means the operating system must manage memory carefully.
The operating system must also manage power consumption carefully.
Less processing power plus fewer processors mean the operating system must carefully
apportion processors to applications.
Identify several advantages and several disadvantages of open-source operating systems. Include
the types of people who would find each aspect to be an advantage or a disadvantage. -
Answer✔Open source operating systems have the advantages of having many people working on
them, many people debugging them, ease of access and distribution, and rapid update cycles.
Further, for students and programmers, there is certainly an advantage to being able to view and
modify the source code. Typically open source operating systems are free for some forms of use,
usually just requiring payment for support services. Commercial operating system companies
usually do not like the competition that open source
operating systems bring because these features are difficult to compete against. Some open
source operating systems do not offer paid support programs. Some companies avoid open
source projects because they need paid support, so that they have some entity to hold accountable
if there is a problem or they need help fixing an issue. Finally, some complain that a lack of
discipline in the coding of open source operating systems means that backward compatibility is
lacking making upgrade
What role do device controllers and device drivers play in a computer system? - Answer✔A
device controller provides for an interface between the peripheral(s) that it controls and the
operating system. It collaborates with the device driver, by means of interrupt, special-purpose
registers and when necessary Direct Memory Access (DMA), to transfer data from/to the
peripheral(s) to/from the buffer storage.
A device driver on the other side understands the device controller and hence provides the rest of
the operating system with a uniform interface to de device.
Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU's
execution load.
How does the CPU interface with the device to coordinate the transfer? - Answer✔The CPU can
initiate a DMA operation by writing values into special registers that can be independently
accessed by the device. The device initiates the corresponding operation once it receives a
command from the CPU.
2|Page
