Assignment 1 Solution

1. What components make up the operating system kernel? [5]
   1. booting and initialisation routines
   2. device drivers
   3. interrupt handlers
   4. file, memory, process and network managers (in monolithic kernels)
   5. message passing (in microkernel systems)
2. Rank the following in terms of speed, fastest to slowest: I/O devices, processor, main memory, registers, secondary storage, users. [3]
   • processor, registers, main memory, secondary storage, I/O devices, users
3. What names are given to operating systems that have the following? [5]
   1. multi-user or time-sharing: more than one user
   2. batch processing: more than one job submitted at a time
   3. multiprogramming: more than one program in memory at a time
   4. multitasking: more than one process sharing the processor
   5. multiprocessing: more than one processor
4. What is the difference between a system call and an interrupt? [4]
   1. a hardware interrupt is generated by hardware such as a disk or I/O peripheral
   2. a system call is a "software interrupt" generated by application software to control hardware
5. List three reasons a system administrator would need to create a file using a command language.
   What are two names for these files? [5]
   1. user account creation and configuration, software installation, system monitoring and logging, file cleanup, backup, etc.
   2. batch files or shell scripts 
6. What type of user interface is used to control the computer by typing a line of text at a prompt?
   What do DOS and UNIX use to make sense of what the user typed? [3]
   1. command-line or command-based user interface
   2. Both use a search path to look for the program to execute the command
   3. DOS uses internal commands via command.com and external commands in a directory like c:\windows\command
   4. UNIX uses a shell program
7. What are the purposes of command switches? [2]
   • provide command options such as names of files to be used in processing
8. What is a search path? [2]
   • a list of folders that the command-line interface searches for a program to execute a command typed by the user
9. How could you use UNIX system calls to start a new program? [2]
   • You could use fork() and/or exec(), depending on whether you wanted to end the current program and/or start an independently running program
10. What factors are considered when scheduling a job using job control language? [5]
    • the priority/importance of the job
    • how much CPU time, I/O time, memory and other resources the job will take or has taken in the past
    • the time when the job was scheduled and any deadline(s) for when it must/should be completed
11. Briefly explain the use of the process stack. [2]
    • The stack is used to store subroutine arguments and return addresses.
    • When a subroutine is called, the arguments and return address is stored at the top of the stack.
    • When returning from the subroutine, the return address is removed from the top of the stack and read.
12. Give two similarities and two differences between a process and a thread.[4]
    • Processes and threads both have program counters and stacks to keep track of instructions and variables.
    • Threads are smaller and more efficient because they share process resources such as the program text.
13. What properties of processes determine which process should use the CPU next? [5]
    • whether the process is owned by a user or the operating system
    • the priority assigned by a user, administrator or the operating system
    • whether the process is batch, interactive or real time
    • resources (CPU time, I/O time, memory) the process has already used or is likely to use (e.g. based on previous use of a program)
    • whether the process is I/O or CPU bound
    • how long the process has been waiting to use the CPU
14. List three types of code files which can be present in memory on a computer running Windows. [3]
    1. Executable file (.exe, .com) or batch file (.bat) (system program or user application)
    2. Library file (.dll)
    3. Device drivers (.sys, .drv)