Chapter 3: Operating Systems

Question 1

What are the functions of operating systems?

Answer 1

• Oversee the operations of a computer
• Store and retrieve files
• Schedule programs for execution
• Coordinate the execution of programs

Question 2

Types of execution of programs

• Jobs
• Batch processing
• Interactive processing
• Real time processing

Answer 2

• Jobs = a program to be executed with its inputs and outputs
• Batch processing = execution of a batch of jobs without any interaction of a user
• Interactive processing = support of interaction between programs and user during execution
• Real time processing = execution of tasks in accordance with deadlines in external real world environment.

Question 3

Multiple users and multiple programs

• Multiprogramming
• Time-sharing
• Multitasking

Answer 3

• Multiprogramming - multiple programs can be executed “at the same time” (originally during batch processing) on a processor.
• Time-sharing = a computer provides service to multiple users “at the same time” (time slices)
• Multitasking = multiple programs can be executed “at the same time” by a single user

Question 4

Operating system components

• User Interface:
• Kernel:

Answer 4

• User Interface:
  Texted based (Shell)
  Graphical User Interface (GUI)
  Window manager

- Kernel:
File Manager
Memory Manager
Device Drivers
Scheduler 
Dispatcher

Question 5

What includes in a File Manager

Answer 5

A file is a named separate group of data

Question 6

What includes a Memory Manager?

Answer 6

• Allocates/deallocates main memory to processes
• Paging: rotates programs and data back and forth between main memory and mass storage
• Virtual memory is when the computer works as if it has more main memory (using paging) than the actual physical main memory.

Question 7

What is included in boot strapping?

Answer 7

• Bootstrapping is the start up process of a computer
• Boot loader is a program stored in ROM, which is run by the CPU when the power is turned on.
• The boot loader transfer the operating system from mass storage to main memory, and then transfers the control (JUMP-instruction) to the operating system

Question 8

What is included in processes?

Answer 8

• Process: the activity of executing a program
• Process state: current status of the activity
  
  • Value of the program counter
  • Value of all the general purpose registers
  • data in associated parts of main memory

Question 9

What is included in process administration?

• Scheduler:

process table:

Dispatcher:

interrupt signal:

Answer 9

• Scheduler: Keeps track of all processes by maintaining a process table (stored in main memory) (Task Manager)
• A process table entry contains process information such as memory area, priority, and whether the process is ready or waiting.
• Dispatcher: controls the allocation of time slices (for execution) to the process in the process table
• At the end of a time slice the CPU receives an interrupt signal and starts executing a program called an interrupt handler

Question 10

Everything on semaphores

• Critical region:
• Mutual Exclusion:
• Semaphore:

Answer 10

• Critical region: a group of instructions that should be executed by only one process at a time
• Mutual Exclusion: The requirement the only one process at a time is allowed to execute a critical region
• Semaphore: A flag that controls a critical region to obtain mutual exclusion
• Test-and-set: a machine instruction that both tests and sets a flag (in the same no interruptible instruction)

Question 11

Everything on deadlock

Answer 11

• Processes block each other from continuing
• Conditions required for deadlock
  
  • competition of non-sharable resources
  • resources requested on a partial basis
  • allocated resources cannot be forcibly retrieved

Question 12

• Spooling

Answer 12

holding data for output at a later more convenient time (ex. printer)

Question 13

Attacks from the outside

• Problems:
• Counter Measures

Answer 13

- Problems: 
  Insecure login (passwords etc)
  Sniffing software - records activities and reports to potential intruders

• Counter Measures
  Auditing software - records and analyzes activities to detect destructive behavior

Question 14

Attacks from within

• Problems:
• Counter Measures

Answer 14

- Problems:
  unruly processes (which try to do destructive activities)

• Counter measures:
  control process activities via privileged mode and privileged instrcutions