What are the three main purposes of an operating system?
The three main purposes are to provide a convenient environment for computer users to execute programs on computer hardware.
Allocate individual resources of the computer as needed to perform the required tasks. The distribution process should be as fair and reasonable as possible.
As a control program, it has two main functions: (1) to supervise the execution of user programs and prevent errors and improper use of the computer; and (2) to manage the operation and control of I/O devices.
What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment?
A: The main disadvantage is keeping the operating system within the time constraints of a real-time system. If the system does not complete a task within a certain period of time, it may cause the whole system to crash. Therefore, when writing an operating system for a real-time system, the author must ensure that his scheduling scheme does not allow the response time to exceed the time limit.
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.
A: An argument in favor of including popular applications in the operating system is that if the application is embedded in the operating system, it may better take advantage of kernel features and therefore have a performance advantage over applications that run outside the kernel. However, the arguments against embedding applications in the operating system are usually dominant:
(1) applications are applications — not part of the operating system.
(2) any performance flaws running in the kernel are offset by security vulnerabilities.
(3) including applications results in a bloated operating system.
How does the distinction between kernel mode and user mode function as a rudimentary form of protection (security) system?
A: The distinction between kernel mode and user mode provides a basic form of protection in the following way. Some instructions can only be executed when the CPU is in kernel mode. Similarly, a hardware device can only be accessed when the program is in kernel mode, and interrupts can only be enabled or disabled when the CPU is in kernel mode. As a result, the CPU has very limited capabilities when executing in user mode, tightening the protection of critical resources.
Give two reasons why caches are useful. What problems do they solve?What problems do they cause? If a cache can be made as large as the device for which it is caching (for instance, a cache as large as a disk),why not make it that large and eliminate the device?
A: Caching is useful when two or more components need to exchange data and the components perform transfers at different speeds. Caching solves the transfer problem by providing an intermediate speed buffer between components. If the fast device data value changes, the data is also in the cache and the cache must be updated. This is especially a problem on multiprocessor systems, where multiple processes may be accessing data. Component can eliminate a cache of equal size, but only if:
(a) the cache and the component have equal state preservationCapability (that is, if a component retains data when power is removed, the cache must retain the data)
(b) the cache is affordable because faster storage tends to be more expensive.
Distinguish between the client–server and peer-to-peer models of distributed systems.
A: The client-server model strictly separates the roles of the client and the server. Under this model, a client requests a service provided by a server. The peer-to-peer model does not have such a strict role. In fact, all nodes in the system are considered peers, and thus can act as either clients or servers, or both. A node may request a service from another peer, or the node may actually provide such a service to other peers in the system. For example, let’s consider a shared cooking dish.The nodal system of the spectrum. Under the client-server model, all recipes are stored in the server. If the client wants to access the recipe, it must request the recipe from the specified server. With the peer-to-peer model, peer nodes can ask other peer nodes for a specified recipe. A node (or possibly a node) with the requested recipe may provide it to the requesting node. Note that each peer can be both a client (it can request recipes) and a server (it can provide recipes).
In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we ensure the same degree of security in a time-shared machine as in a dedicated machine? Explain your answer.
A:Two potential issues in multiprogramming and time-sharing environments include:
1.Data Leakage: Simultaneous access to the system by multiple users may increase the risk of data leakage. Without proper isolation measures, one user may access another user’s data, leading to information disclosure.
2.Denial of Service (DoS) Attacks: In a multi-user shared system, some users may execute malicious operations to exhaust system resources, thereby impacting the services of other users. In such cases, the system may suffer from denial of service (DoS) attacks.
Ensuring the same level of security as dedicated machines in time-sharing environments is challenging. Time-sharing systems need to serve multiple users simultaneously, allowing concurrent access to system resources. This shared resource characteristic increases the risk of attacks on the system. In contrast, dedicated machines typically grant access to only one user or a trusted group of users, enabling stricter security measures for enhanced security. While security measures such as access control, encryption, and auditing can be implemented to strengthen the security of time-sharing systems, the shared resource nature makes it impossible to guarantee the same level of security as dedicated machines.
Describe some distributed applications that would be appropriate for a peer-to-peer system
A:Some distributed applications suitable for peer-to-peer systems include:
- File sharing applications: Allow users to share and exchange files on a peer-to-peer network, such as BitTorrent.
- Blockchain applications: Utilize peer-to-peer networks to distribute and verify transaction data, such as Bitcoin and Ethereum.
- Real-time communication applications: Enable users to communicate directly in real-time on a peer-to-peer network, such as Skype and WhatsApp.
- Distributed computing applications: Utilize multiple nodes in a peer-to-peer network to collectively process computing tasks.
- Decentralized social networks: Allow users to create profiles, share content, and engage in social interactions on a peer-to-peer network, such as Diaspora and Mastodon.
- Content Delivery Networks (CDNs): Utilize peer-to-peer networks to distribute network content to improve access speed and stability, such as BitTorrent CDN.
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.
A:Advantages of open-source operating systems:
1.Transparency and security: Open-source operating systems allow users to inspect the source code, enhancing transparency and security. Developers and security-conscious users find this advantageous as they can quickly identify and fix vulnerabilities.
2.Customizability: Open-source operating systems provide extensive customization options. This flexibility attracts power users, developers, and organizations needing tailored solutions to meet specific requirements.
3.Community support: Open-source projects typically have vibrant communities of developers and users who provide ongoing support, assistance, and knowledge sharing. This collaborative environment is beneficial for individuals seeking help, troubleshooting, or new features.
4.Cost-effectiveness: Open-source operating systems are often available for free, eliminating licensing costs. This cost-effectiveness is particularly advantageous for budget-conscious individuals, small businesses, educational institutions, and organizations operating in developing countries.
5.Innovation and rapid development: The openness of the development process fosters innovation and rapid iteration. Developers can freely experiment, iterate, and integrate new features, enabling continuous improvement and staying ahead.
Disadvantages of open-source operating systems:
1.Complexity and learning curve: Open-source operating systems can be highly complex, with a steep learning curve for beginners. Individuals accustomed to more user-friendly interfaces may find configuration and management challenging.
2.Limited compatibility with proprietary software: Some proprietary software may be incompatible with open-source operating systems, potentially leading to compatibility issues. Users relying on specific proprietary applications or hardware may encounter difficulties or need to seek alternative solutions.
3.Fragmentation and lack of standardization: The diverse ecosystem of open-source operating systems can lead to fragmentation and lack of standardization. This may result in compatibility issues between different distributions or versions, posing challenges for users seeking environment consistency.
4.Limited vendor support: Unlike proprietary operating systems, open-source alternatives may lack dedicated vendor support. While community support may be strong, it may not be sufficient for enterprise-level requirements or urgent issues, requiring additional support and maintenance resources.
5.Security risks: While the transparency of open-source software enhances security in many cases, it may also expose vulnerabilities to malicious users. Without proper management and timely updates, open-source operating systems may become targets for attacks, posing risks to users and organizations.
