操作系统 (OS)是一种软件，它充当计算机硬件组件和用户之间的接口。每个计算机系统都必须至少有一个操作系统才能运行其他程序。浏览器、MS Office、记事本游戏等应用程序需要一些环境来运行和执行其任务。
以下是常见操作系统的市场份额：
| OS Name | Share |
| Windows | 40.34 |
| Android | 37.95 |
| iOS | 15.44 |
| Mac OS | 4.34 |
| Linux | 0.95 |
| Chrome OS | 0.14 |
| Windows Phone OS | 0.06 |
操作系统功能
一些典型的操作系统功能可能包括管理内存、文件、进程、I/O 系统和设备、安全等。
在操作系统中，软件执行每个功能：
- 进程管理：进程管理帮助操作系统创建和删除进程。它还提供了进程之间的同步和通信机制。
- 内存管理：内存管理模块执行为需要此资源的程序分配和取消分配内存空间的任务。
- 文件管理：它管理所有与文件相关的活动，例如组织存储、检索、命名、共享和文件保护。
- 设备管理：设备管理跟踪所有设备。该模块也负责此任务，称为 I/O 控制器。它还执行设备的分配和解除分配任务。
- I/O 系统管理： 任何操作系统的主要目标之一是向用户隐藏硬件设备的特性。
- 辅助存储管理：系统具有多个存储级别，包括主存储、辅助存储和缓存存储。指令和数据必须存储在主存储器或高速缓存中，以便运行程序可以引用它。
- 安全：安全模块保护计算机系统的数据和信息免受恶意软件威胁和授权访问。
- 命令解释：该模块解释由和代理系统资源给出的命令以处理该命令。
- 网络： 分布式系统是一组不共享内存、硬件设备或时钟的处理器。处理器通过网络相互通信。
- 工作会计：跟踪各种工作和用户使用的时间和资源。
- 通信管理：计算机系统不同用户的编译器、解释器和其他软件资源的协调和分配。
操作系统优势
- 允许您通过创建抽象来隐藏硬件细节
- 易于使用 GUI
- 提供用户可以执行程序/应用程序的环境
- 操作系统必须保证计算机系统使用方便
- 操作系统充当应用程序和硬件组件之间的中介
- 它以易于使用的格式提供计算机系统资源
- 充当系统所有硬件和软件之间的中介
操作系统的缺点
- 如果操作系统出现任何问题，您可能会丢失系统中存储的所有内容
- 操作系统的软件对于小型组织来说是相当昂贵的，这增加了他们的负担。
- 它永远不会完全安全，因为威胁随时可能发生
OS代写：Operating Systems COMP3231代写案例
Question 1
A)
Consider a demand-paging system with a paging disk that has an average access and transfer time of 5 milliseconds for a single page. Addresses are translated through a page table in main memory, with an access time of 100 nanoseconds per memory access. Thus, each memory reference through the page table takes two accesses. The system has a 48-entry TLB to speed up memory accesses.
Assume that 99% of memory accesses result in a TLB hit, and of the remaining 1%, 5 percent (or 0.05% of the total) cause page faults. What is the effective memory access time?
B)
Some versions of UNIX store the first part of each file in the same disk block as the inode. Discuss why this might be advantageous in practice.
Question 2
A)
Suppose that the head of a moving-head disk with 192 tracks, numbered 0 to 191, is currently serving a request at track 80 and has just finished a request at track 62. The queue of requests is kept in the FIFO order: 119, 58, 114, 28, 111, 55, 103, 30, 75. What is the total number of tracks traversed by head movements needed to satisfy these requests for the following disk-scheduling algorithms?
i) FCFS.
ii) SSTF.
iii) Elevator (SCAN).
iv) Modified Elevator (C-SCAN).
B)
User-level threads packages generally implement cooperative scheduling. What is cooperative scheduling, and why is it the common method used to schedule user-level threads?
Question 4
Answer this question in a separate book
Explain how a 32-bit virtual address is translated into a physical address on a system using a two-level
page table and 4kb pages. Your explanation, where it refers to parts of an address, must specifically state
which bits of the address you are talking about. (Ignore any TLB). State any assumptions you make!
Question 3
Answer this question in a separate book Explain how a 32-bit virtual address is translated into a physical address on a system using a two-level page table and 4kb pages. Your explanation, where it refers to parts of an address, must specifically state which bits of the address you are talking about. (Ignore any TLB).
Question 5
Answer this question in a separate book
A)
Describe the difference between external and internal fragmentation. Indicate which of the two are most likely to be an issues on a) a simple memory memory mangement machine using base limit registers and static partitioning, and b) a similar machine using dynamic partitioning.
B) Describe the difference between a normal test-and-set spinlock and a read-before-test-and-set spin- lock. Why would the latter be advantageous over the former on multiprocessor systems.
