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450 > Midterm > Flashcards

Midterm Flashcards

1
Q

What is the kernel

A

The core of the OS. The one program running at all times on the computer

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2
Q

Process

A

A program in execution; instance of a program being executed by OS

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3
Q

3 components of a process

A
  • (code)Executable program
  • (data) Associated data needed by the program
  • (context) The execution context of the process which contains all information the OS needs to manage the process (ID, state, CPU registers, stack)
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4
Q

What is and where is PCB?

A

Process Control Block is included in the context, along with the stack
It is snapshot that contains all necessary and sufficient data to restart a process where it left off (ID, state, CPU registers)
- concrete representation of a process

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5
Q

Where in OS is PCB?

A

It is one entry in the OS’s process table (array of linked list)

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6
Q

What is in user address space of process?

A

Program code
Data

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7
Q

What is in context of process

A

PCB
Stack

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8
Q

What are 3 main components of PCB?

A

Identification
CPU State info (registers, PC, stack pointer)
Control info (Schedule and state info, links to other processes, memory limits, open files)

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9
Q

5 states of process and what they mean

A

New: process is being created
Ready: The process is waiting to be assigned to a processor
Running: Instructions are being executed
Waiting: The process is waiting for some event to occur
Terminated: The process has finished execution

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10
Q

New to ready process

A

admitted

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11
Q

Ready to running process

A

scheduler dispatch

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12
Q

Running to ready process

A

Interrupt

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13
Q

Running to waiting process

A

I/O or event wait

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14
Q

Waiting to Ready process

A

I/O or event completion

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15
Q

Running to terminated process

A

exit

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16
Q

What is batch system?

A

A computer system that processes jobs in groups, or batches, without direct user interaction

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17
Q

4 ways a process can be created

A

System boot
User requests to run application
Existing process spawns a child process
Batch system takes next job in line

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18
Q

3 ways process is terminated

A

Regular completion, with or without error code
Fatal error (uncatchable of uncaught)
Killed by another process via the kernel

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19
Q

Return value of fork to parent and child

A

positive value to parent
0 to child

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20
Q

what does execvp do

A

replace the existing program

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21
Q

Fork example 1

A

process 13

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22
Q

2 events that lead to process pause/dispatch

A
  • I/O Wait - OS triggered
  • Preemptive timeout - hardware interrupt triggered
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23
Q

What 5 things happen when a current process calls create()

A
  • PCB is allocated and initialized
  • The parent field of the new process will be set to self (running process)
  • new process P is added to the children list of the currently running process
  • The new process P is put in ready list
  • The scheduler may choose to dispatch to new process or continue the parent
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24
Q

What is and happens during a process context switch

A

When cpu switches to another process, the system must save the state of the old process and load the saved state for the new process

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25
Q

Is context switching useful work?

A

No

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26
Q

Is there a difference between a new process and the other processes? can you tell this is a new one?

A

if OS has a toll how long a process has been run for, but otherwise they are very similar

27
Q

Process Context Switching 7 steps

A
  • Save cpu context, including PC and registers
  • Update process state and other fields of PCB
  • Move the PCB to appropriate queue
  • Select another process for execution: made by CPU scheduling algorithm
  • Update the PCB of selected process (switch to running)
  • Update memory management structures
  • Restore CPU context to the values contained in the new PCB
28
Q

What events trigger OS to switch processes? 3

A

Interrupts
Exceptions
System Calls

29
Q

Interrupts event

A

External, asynchronous events, independent of the currently executing process instructions

30
Q

Exceptions events

A

Traps, internal synchronous (but involuntary) events caused by instructions: OS may terminate or recover process

31
Q

System Call events

A

Traps, voluntary synchronous events calling a specific OS service.

32
Q

Job queue

A

Set of all jobs in the system

33
Q

Ready Queue

A

Set of all processes residing in main memory, ready and waiting to execute

34
Q

Device Queue

A

Set of processes waiting for I/O device

35
Q

Long term scheduler

A

The decision to add a program to the pool of processes to be executed (job scheduling)

36
Q

Medium term scheduling

A

The decision to add to the number of processes that are partially or fully in main memory (swapping)

37
Q

Short term scheduling

A

CPU Scheduling, the decision as to which available processes in memory are to be executed by the processor (dispatching)

38
Q

Draw scheduler pic

A

process 31

39
Q

Long term scheduler controls

A

the degree of multiprogramming

40
Q

Which scheduler is invoked more frequently?

A

Short term scheduler

41
Q

io bound process vs cpu bound process

A

io bound spends more time doing io than computations, many short cpu bursts, and vice versa

42
Q

examples of io bound and cpu bound

A

chat applications, interactions // photo editors, gaming

43
Q

What does Long term scheduler have to do

A

Needs to make careful decisions, decides what comes and stays on system at current time, decides when process terminates

44
Q

What happens if io scheduled first, what if cpu scheduled first?

A
  • little cpu utilization, and u have many things to do, cpu not fully working
  • lost interactivity, io tasks waiting intensively for cpu tasks to finish, even though they only need a little cpu
45
Q

swapping

A

memory management technique that temporarily swaps processes from main memory to secondary memory and vice versa, helps increase degree of multi-programming and increase main memory utilization

46
Q

Mechanisms for processes to communicate and synchronize their actions

A

Shared memory
Message passing

47
Q

Shared memory

A

By using the same address space and shared variables

48
Q

Message Passing

A

Processes communicate with each other without resorting to shared variables

49
Q

Message passing - direct communication

A

Processes know who they are talking to. They must name each other explicitly

50
Q

Message Passing - indirect communication

A

Processes dont know who they are talking to. Messages are directed and received from mailboxes

51
Q

Message passing - blocking

A

Synchronous, The sender blocks until the message is received, the receiver blocks until the message is available. Ex:

52
Q

Message Passing - Non-blocking

A

Asynchronous, sender send message and continues, receiver receives a valid message or null Ex: streaming service, drone sending signal

53
Q

What to do with multiple messages

A

Use Buffer, queue of messages attached to the link, implemented in zero, bounded, or unbounded

54
Q

Time sharing, each process is given a

A

Multiple processes running on one physical cpu. Virtual CPU

55
Q

Virtual CPU

A

A cpu that the process assumes is available only to itself

56
Q

Benefits of virtual cpu 3

A

Multi user support
Multi CPU transparency
Portability

57
Q

Two ways to organize PCBs

A

Array of Structures -> wasted memory
Array of pointers to dynamically allocated PCBs -> overhead of dynamic memory management

58
Q

Waiting list

A

Contains all processes blocked on a resource

59
Q

Ready List

A

Contains all processes that are in ready state and able to run on CPU

60
Q

A resource is allocated to a process if

A

the process has access to and is able to utilize the resource

61
Q

A resource is free if

A

the resource may be allocated to a requesting process

62
Q

Scheduler function

A

Determines which process should run next and starts the process

63
Q
A

450 (7 decks)

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