Operating Systems

Name: Mathijs
Student number: 12345678

Questions

  1. We start with the queue R, S, T in order. The elements in the queue are ordered according to first-in, first-out (FIFO). Next, we remove the first element from the queue, which is R the element that arrived first. Now the queue is S, T. Then, we add the fourth element X to the queue. The queue is now ordered as S, T , X. Then we remove the first element, so T, X. Finaly, we add the elements Y and Z to the queue. Thus, the queue ends up as T, X, Y, Z.
  2. The user interface is the part of the operating system that allows for communication between the users of the computer and the operating system. The user interface acts as an intermediary between the user and the kernel, which is the internal part of the operating system. An older user interface called a shell is a program that allows the user to give commands to the operating system through a keyboard and monitor. Newer computer systems use a graphical user interface (GUI), where the programs and files are projected visually on the monitor. The user can read files and execute programmes using input devices, such as keyboard, mouse, and touch screens. The book: Operating system from Brookshear, Computer Science: An Overview.
  3. The kernel is the core part of the operating system. The kernel provides the infrastructure that the other applications require. Its main responsibilities are distributing computer resources to the processes, device drivers, file management, and memory management. The file manager keeps track of the files stored in mass storage, accessibility to the files, and storage space for new files and file extensions. In contrast, the memory manager allocates main memory to running programs. Another kernel component is called the scheduler that creates a process table whose entries are the programs that need to be executed, and the table contains information on which process is ready or waiting, and which processes have priority. The execution of these processes is managed by the dispatcher another component of the kernel. Finaly, device drivers enable the operating system to communicate with peripheral devices such as printers, monitors, and speakers, by translating requests from the computer to technical instructions that the peripheral device can understand. The book: Operating system from Brookshear, Computer Science: An Overview.
  4. The path X/Y/Z implies a tree/hierarchical directory structure. This can be seen from the fact that the starting directory has a subdirectory Y , which itself has a subdirectory Z. Additionally, the relative path shows that the directories do not have access to files in other directories.
  5. A process with a waiting status requires some external event for its progress to proceed, such as input from the user or output from another process. In contrast, a process with a ready status can continue without waiting for some external event to occur.
  6. The CPU points to a space in main memory that stores the first process that will be executed when the computer is turned on. We want the operating system to be the first process to be executed by the CPU, however, the operating system cannot be stored in main memory since main memory is volatile, which means that the memory is lost when the computer is turned off. Therefore, the operating system is stored in mass memory. Main memory has a few non-volatile memory cells called the read- only memory (ROM). On this memory a program called the boot loader is stored and this program is the first program that is executed by the CPU when the computer is turned on. This program transfers the operating system from mass memory to main memory; this procedure is called booting. Then, the operating system takes control over the computer. Thus, without the boot loader the operating system would not be transferred to main memory, and the computer would not operate. If the operating system is stored on the ROM, then the computer could function without the boot loader. However, storing the operating system on the ROM would be inefficient since this would require a lot of non-volatile memory in the main memory.
  7. The read only memory (ROM) is non-volatile memory. Firmware is software that provides low level instructions to the computer and is not readily changeable. The firmware is usually stored on the ROM, and an example of firmware is the boot loader. Since the ROM is read only, it follows that the firmware cannot be changed. However, nowadays, firmware is stored on flash memory, which is non-volatile memory that is reprogrammable. Thus, the firmware can be updated. On the other hand, the operating system is stored in mass memory and is updated frequently to keep up with new device drivers and to maintain security.
  8. With a 4-digit code and 10 possible symbols 0 to 9, there are 10^4=10000 possible 4- digit permutations or codes. If checking each 4-digit code takes 1 second, then it will take at most 10^4 * 1 seconds = 10^4 * (1/60^2) hours = 25/9 hours = 2.78 hours. However, if the code is 0000, then the first attempt is correct, and it would only take 1 second.
  9. With a 6-digit code and 62 possible symbols 0 to 9 and 26 lowercase and uppercase letters, then there are 62^6=56800235580 possible 6-digit permutations or codes. If checking each 6-digit code takes 1 second, then it will take at most 62^6 * 1 seconds= 62^6 * (1/60^2) hours = 62^6 * (1/60^2) * (1/24) days = 62^6 * (1/60^2) * (1/24) * (1/365) years = 1801.12 years. However, if the code is 000000, then the first attempt is correct, and it would only take 1 second.
  10. The intruder knows the most common passwords and will attempt these passwords first. Then, the intruder will attempt the most common passwords and replace letters with numbers such as E and 3. Since the intruder knows the most common replacement, it will code the program to try these common replacements. Furthermore, the substitutions are systematic not random, making them easily predictable.
  11. The password is encrypted; this means that the password is scrambled and can only be decrypted using the key. The company of the webpage does not have access to this key, so cannot read your password. Therefore, the company cannot give your password back.
  12. Two factor authentication requires the username, password, and an additional format of information. An example could be a 1 time use code that can only be used for a short amount of time and that is send from an application of your phone that also might require face recognition. Since the intruder would need your username, password, phone, and face it would be costly for the intruder to steal your phone.

References

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