sample_Midterm_2

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Instructions Note : This is a sample exam – do not submit it! The instructions below will be provided during the actual Midterm exam and are here to help you practice! During the exam, you are ALLOWED to use the textbook, the lectures notes, any notes taken by you, the sample exams, a calculator, Web search engines, Google, etc. During the exam, you are DISALLOWED to talk to/ask any person (except for the instructor), either in-person or online, about any part of the exam. Type the answers inside this very questionnaire file (in the text boxes under the ques- tions) and submit the file by attaching it on Blackboard at Exams → Midterm . Exam duration: 03:40 PM – 04:55 PM. Exam Location: at the West End Building (WEB), 1st floor, computers M126 – M165. Any Questions? I will approach you when I finish answering questions your class- mates asked earlier. Tip: Use the slide numbers + links listed under questions to look up answers and hints. Tip: You can always give a short explanation if you are unsure about an answer to get partial credit. Tip: You can submit the exam ∞ times until it is due. The last attempt is the one to be graded. Sections & Points in the Midterm : Section # of Questions Points per Question Topic 1: Overview of operating systems – Short Answer 2 10 Topic 2: Functions & Services of an OS – Short Answer 2 10 Topic 3: I/O and Interrupts – Short Answer 2 10 Topic 4: Processes – Short Answer 2 10 Topic 5: Threads – Short Answer 2 10 Extra Credit – Short Answer 5 2 # of Questions Points Total (without Extra Credit) 10 100 Total (with Extra Credit) 15 110 Updated: 02/04/2024, 03:40 1 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Topic 1: Overview of operating systems – Short Answer Instructions: Respond to each of the following question by typing a (textual) answer into the boxes provided under each question. The response to each question should be at least 2 sentences in length (unless otherwise noted,) and must be written using your own words. 1. Operating systems can be divided into types, such as real-time OS, batch OS, etc. Suppose you landed a computer engineer job, and your boss assigned you to make decisions on a new operating system that your company will soon create. Specifically, your task is to decide what type the operating system will be. What type would you recommend to your boss if you know that the device that runs this operating system must alert a soldier in a battlefield as fast as possible when an enemy soldier is approaching ? Explain your answer. (Slides: Topic 1, slides 14 – 16. Link (copy and paste in a new browser tab/window:) ) (10 points) 2. (a) In 1-3 sentences, explain briefly what a Main Memory device is (i.e., what is its purpose?) (b) Is Main Memory an input device, output device, or storage device? Explain your answer in at least one sentence. (Slides: Topic 1, slides 18 – 24. Link (copy and paste in a new browser tab/window:) ) (10 points) Updated: 02/04/2024, 03:40 2 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Topic 3: I/O and Interrupts – Short Answer Instructions: Respond to each of the following question by typing a (textual) answer into the boxes provided under each question. The response to each question should be at least 2 sentences in length (unless otherwise noted,) and must be written using your own words. 5. Slides 26 through 30 discuss 5 categories of I/O devices. One of these categories is Block and Character devices. Describe the main difference between Block and Character devices. (Slides: Topic 3, slides 26 – 30. Link (copy and paste in a new browser tab/window:) ) (10 points) 6. The slides for Topic 3 starting at slide 13 introduce various methods in which an operating system can handle I/O events. State one advantage that Interrupt-driven I/O has over Polling I/O , and explain what aspect in the architecture/mechanics of Interrupt-driven I/O leads to the advantage you mentioned in the previous part. (Slides: Topic 3, slides 13 – 20. Link (copy and paste in a new browser tab/window:) ) (10 points) Updated: 02/04/2024, 03:40 4 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Topic 4: Processes – Short Answer Instructions: Respond to each of the following question by typing a (textual) answer into the boxes provided under each question. The response to each question should be at least 2 sentences in length (unless otherwise noted,) and must be written using your own words. 7. (a) What is a zombie program? (b) Does a zombie exist forever? What happens to it after some time? (Slides: Topic 4, slides 25 – 26. Link (copy and paste in a new browser tab/window:) ) (10 points) 8. Explain the difference between the fork() system call and the exec() system call. (Slides: Topic 4, slides 19 – 20. Link (copy and paste in a new browser tab/window:) ) (10 points) Updated: 02/04/2024, 03:40 5 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Extra Credit Instructions: Respond to each of the following question by typing a (textual) answer into the boxes provided under each question. The response to each question should be at least 2 sentences in length (unless otherwise noted,) and must be written using your own words. Topic 1: Overview of operating systems 11. A short scenario is given below this paragraph. Does this scenario describe (1) a security issue , (2) a protection issue , or (3) no issue at all (neither a security nor a protection issue)? Explain your answer. Scenario : Two processes are running on the computer: Process A and Process B. Process A miscalculates the size of an array that it allocated and mistakenly accesses and overwrites data at a location beyond the array’s size. This location was allocated by Process B. (2 points) Topic 2: Functions & Services of an OS 12. Starting with slide 22 of Topic 2, we describe what system calls are and why they are critical to keeping the OS functioning properly. A further slide also mentions several examples of system calls in Linux and Windows. (a) Describe what the send() Linux system call does in at least 2 sentences. ( Hint : Find the manual page on the send() system call.) (b) Slide 25 mentions 6 general categories to which each system call of an operating system belongs. State to which category the send() Linux system call belongs, and explain why in at least one sentence. (2 points) Updated: 02/04/2024, 03:40 7 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm CUNY Brooklyn College Topic 3: I/O and Interrupts 13. The operating system provides several I/O-related services to processes and users. In at least one sentence, explain one benefit that the service of I/O Buffering will grant to the process or user that requests this service. (2 points) Topic 4: Processes 14. (a) Explain what the section data of a process in memory stores/keeps. (b) In which one memory section are dynamically-allocated objects stored? (2 points) Topic 5: Threads 15. Threads that belong to the same process share many resources that the process is providing to them. On the other hand, some resources are individual to each thread. Is the program counter register a resource that all the threads share between one another or a per-thread resource? Explain your answer. (2 points) – End of Sample Midterm Exam – Updated: 02/04/2024, 03:40 8 of 11 Return to Top of Syllabus ↰

Spring 2024 CISC 3320 MW3 Sample Midterm Solutions Brooklyn College Sample Midterm Exam Solutions Topic 1: Overview of operating systems – Short Answer 1. Operating systems can be divided into types, such as real-time OS, batch OS, etc. Suppose you landed a computer engineer job, and your boss assigned you to make decisions on a new operating system that your company will soon create. Specifically, your task is to decide what type the operating system will be. What type would you recommend to your boss if you know that the device that runs this operating system must alert a soldier in a battlefield as fast as possible when an enemy soldier is approaching ? Explain your answer. (Slides: Topic 1, slides 14 – 16. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: Devices that work in military conditions must respond within a given amount of time since the soldiers’ lives depend on them. As such the operating system must be a real-time operating system. 2. (a) In 1-3 sentences, explain briefly what a Main Memory device is (i.e., what is its purpose?) (b) Is Main Memory an input device, output device, or storage device? Explain your answer in at least one sentence. (Slides: Topic 1, slides 18 – 24. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: (a) Main Memory, also frequently referred to as RAM, is a short-term ,volatile data storage device. This is where programs are being loaded (copied to) to start running as processes. (b) Since the purpose of Main Memory is to store data, it is a storage device. Topic 2: Functions & Services of an OS – Short Answer 3. Data structures are ubiquitously employed by operating systems to help the OSes organize data correctly and efficiently. We mentioned some data structure types in Topic 2. Mention one data structure that is mentioned anywhere in Topic 5: Threads , and explain what its purpose or use is in the context of this chapter using your own words . (Slides: Topic 2, slides 13 – 21. Link (copy and paste in a new browser tab/window:) Updated: 02/04/2024, 03:40 1

Spring 2024 CISC 3320 MW3 Sample Midterm Solutions Brooklyn College ) (10 points) Correct answer: (Example:) A thread’s stack is a data structure that each thread maintains. In the stack, a thread will store the data of a function call and various local variables that are declared within every function call. Since a function could be called inside another function, it turns out that recording this information is similar to “stacking” details one upon the other, until we exit a function, which is why a stack is being used. 4. Booting is a synonym for launching an operating system on a device and occurs in a few stages. Suppose that the bootstrap program finished copying the instructions of the operating system to memory and the OS started running . Describe the im- mediate next step in the booting process (that is, describe what will occur next on) in one or more sentences. (Slides: Topic 2, slides 42 – 43. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: Once the kernel is copied to memory so that the operating system starts running, the operating system will mount the root file system by finding where the root directory is stored on disk and establishing access to the root directory. Topic 3: I/O and Interrupts – Short Answer 5. Slides 26 through 30 discuss 5 categories of I/O devices. One of these categories is Block and Character devices. Describe the main difference between Block and Character devices. (Slides: Topic 3, slides 26 – 30. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: A block device is one that lets the operating system access data block-by-block. A block is some multiple of 512 bytes, so the OS cannot access less than 512 bytes in a shot. A character device is one that lets the operating system access data character-by-character. 6. The slides for Topic 3 starting at slide 13 introduce various methods in which an operating system can handle I/O events. State one advantage that Interrupt-driven I/O has over Polling I/O , and explain what aspect in the architecture/mechanics of Interrupt-driven I/O leads to the advantage you mentioned in the previous part. Updated: 02/04/2024, 03:40 2

Spring 2024 CISC 3320 MW3 Sample Midterm Solutions Brooklyn College If the computer where the program is destined to run has 3 CPUs, and the portion of the program that is supposed to manifest multi-threading is 61% , what would be the maximum possible overall speedup of the whole program? Fully show your computation! (as on the example on slide 25.) Hint : Use Amdahl’s Law. (Slides: Topic 5, slides 24 – 25. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: [The explanation in these square brackets is for you. You can include it in your answer on the exam if you want or not, but you must include the calculation that follows after closing the square brackets: Using Amdahl’s Law, which is Speedup = 1 (1 − p ) + p n , you can compute the maximum possible speedup of the program (which, by the way, happens when you create exactly 3 threads [same as the number of CPUs, not less and not more] to run that section that should manifest multi-threading.) The quantity p is the portion of the program to manifest multi-threading; however, you should first convert 61% to a fraction between 0 and 1, which is 0.61. The quantity n is the number of CPUs, which is just 3.] When you plug p = 0.61 and n = 3 into the equation, you find that the speedup is: Speedup = 1 (1 − p ) + p n = 1 (1 − 0 . 61) + 0 . 61 3 = 1 0 . 39 + 0 . 2033 = 1 0 . 5933 = 1 . 6855 . 10. Mention exactly one advantage and exactly one disadvantage in implementing/apply- ing the One-To-One threading model . (Slides: Topic 5, slides 15 – 18. Link (copy and paste in a new browser tab/window:) ) (10 points) Correct answer: Advantage: It is easier to code (implement) this model. [Alter- native answer: if one thread blocks, such as due to waiting for i/o, other threads can continue working normally, without the need to wait as well.] Disadvantage: The operating system will spend a lot of extra time doing context switches between the kernel threads (since we have as many kernel threads as user threads – which can be a lot.) Updated: 02/04/2024, 03:40 4

Spring 2024 CISC 3320 MW3 Sample Midterm Solutions Brooklyn College Extra Credit Topic 1: Overview of operating systems 11. A short scenario is given below this paragraph. Does this scenario describe (1) a security issue , (2) a protection issue , or (3) no issue at all (neither a security nor a protection issue)? Explain your answer. Scenario : Two processes are running on the computer: Process A and Process B. Process A miscalculates the size of an array that it allocated and mistakenly accesses and overwrites data at a location beyond the array’s size. This location was allocated by Process B. (Slides: Topic 1, slides 28 – 31. Link (copy and paste in a new browser tab/window:) ) (2 points) Correct answer: Process A is rightfully running on the computer, and uninten- tionally changes data that belongs to Process B. As such, this scenario a protection issue . Topic 2: Functions & Services of an OS 12. Starting with slide 22 of Topic 2, we describe what system calls are and why they are critical to keeping the OS functioning properly. A further slide also mentions several examples of system calls in Linux and Windows. (a) Describe what the send() Linux system call does in at least 2 sentences. ( Hint : Find the manual page on the send() system call.) (b) Slide 25 mentions 6 general categories to which each system call of an operating system belongs. State to which category the send() Linux system call belongs, and explain why in at least one sentence. (Slides: Topic 2, slides 22 – 26. Link (copy and paste in a new browser tab/window:) ) (2 points) Correct answer: (a) The send() system call lets a process send a message to another process via a socket connection that was established between the two processes. We can use the send() system call only when the socket device is considered “connected”. (b) Because send() can be used to control the communication between processes, it is part of the category of Process Communication. Updated: 02/04/2024, 03:40 5