Os Intro And History

Front 1

What is an Operating System?

Back 1

An operating system (OS) is software,consisting of programs and data, that runs on computers and manages computer hardware
resources and provides common services for efficient execution of various application software.

Front 2

What resources the OS manages?

Back 2

Central Processing Unit (CPU)
Memory
Storage
Input/Output Devices

Front 3

What are the objectives when the OS manages the computer system resources?

Back 3

Efficiency and Fairness

Front 4

OS provides a set of common services which are

Back 4

System calls (interface to programmer)
User Interfaces (interface to user)

Front 5

abstraction layer

Back 5

provides a universal interface to the hardware
despite the possibility of supporting several
different hardware devices

Front 6

Kernel

Back 6

resource management
Processor, Memory, and I/O

Front 7

Moore’s Law

Back 7

# of transistors on a
single chip doubles
every 18 months

Front 8

Charles Babbage

Back 8

Difference Engine
Designed to automate the computation of mathematical
tables using difference method

Front 9

Exception

Back 9

An unscheduled event that disrupts program
execution (internally generated)

Front 10

Interrupt

Back 10

An unscheduled event that disrupts program
execution (externally generated)

Front 11

Process

Back 11

an instance of a program executing on a
CPU
§ Different from a program

Front 12

Process Management 5

Back 12

Creating and deleting processes
Suspending and resuming processes
Providing mechanisms for communication
Providing mechanisms for synchronization
scheduling processes

Front 13

5 Parts of a Computer System

Back 13

Processor(1: Control Path,2: Data Path)
3: Memory
4: Input
5: Output

Front 14

Who created the first electronic computer (around WWII) that had a general purpose and was operational?

Back 14

John Presper Eckert/John Mauchly (UPenn)

Front 15

First electronic general purpose computer

Used by the military to compute artillery firing tables & which data entered on punch cards

Back 15

ENIAC (Electronic Numerical Integrator and Calculator)

Front 16

Who developed the the idea of storing the program in memory along with the data (Stored program concept)?

Back 16

John von Neumann

Front 17

Functionality of a batch monitor

Back 17

Load program, run, print results

Front 18

Name of the first real commercial computer, 48 were built & that correctly predicted the outcome of the 1952 presidential election

Back 18

UNIVAC (Universal Automatic Computer) [Remington-Rand]

Front 19

Which company and in what year implemented the use of the microprocessor (computer on a single IC)?

Back 19

Two companies:

§ Intel Corporation (est. 1968)
§ Intel 4004 [1971]

Front 20

Which computers were the first ones to be called microcomputers (since they used microprocessors)?

Back 20

Altair 8800 (1975)

Apple I (1976)

Front 21

First personal computers that had:

- GUI

- LAN

Back 21

Xerox Alto in 1973 (non-commercial)

Apple II in 1977

Front 22

First packet switching network funded

Back 22

ARPANET (later became the Internet)

Front 23

Which university became the first node in 1969

Back 23

UCLA

Front 24

Cloud computing

Back 24

Most of the processing is done on a compute server in the network somewhere

Most of the storage is on a file server in the network somewhere

Front 25

Why allow cooperating processes/threads?

Back 25

§ Speedup – overlap I/O and Computation, take
advantage of parallelism for multiprocessor systems
§ Modularity – divide and conquer

Front 26

Why are cooperating processes important?

Back 26

Need to ensure correct operation with concurrent processes/threads
§ If process/thread scheduler can schedule threads in any way, programs must work under all circumstances
§ Processes/threads can be run truly concurrently or interleaved in any manner

Front 27

why can Cooperating processes affect each other’s execution?

Back 27

They share a logical address space or share data through files and messages

Front 28

Why can Concurrent access to shared data result in intermittent incorrect behavior?

Back 28

Because the outcome may be affected by concurrency or interleaving of the execution

Front 29

Independent processes

Back 29

Scheduling order does not affect operation

Front 30

Cooperating processes/threads

Back 30

Shared state between threads, scheduling order can affect operation without proper synchronization among processes/threads

Front 31

Race Condition

Back 31

When several processes access and manipulate the same data concurrently and the outcome of the execution depends on the order in which the access takes place

Front 32

What should happen to ensure correct operation in certain code sequences?

Back 32

They should be uninterruptable and/or should
not be executed at the same time in more than one process/thread (critical section)

Front 33

Why are race conditions bad?

Back 33

Race conditions lead to non–deterministic behavior

Front 34

How can race conditions be avoided?

Back 34

Ensure that only one of process
can manipulate shared data at a time

Front 35

Mutual Exclusion

Back 35

Ensuring that only one thread does a

particular thing at a time

Front 36

Critical Section

Back 36

Piece of code that only one thread can execute at once. Only one thread at a time will get into this section of code.

Front 37

What requirements should be satisfied by a solution to the critical section problem?

Back 37

Mutual Exclusion
Progress
Bounded waiting

Front 38

Bounded waiting (avoid starvation)

Back 38

There must exist a bound on the number of times other processes are allowed to enter their critical section after a process has made a request to enter its critical section and before it is allowed to

Front 39

Peterson’s Algorithm

Back 39

Use a turn variable to signal whose turn it is to enter the critical section as well as a flag per process that indicates whether a process wants to enter its critical section

Front 40

Locking mechanism to
ensure mutual exclusion

Back 40

Disabling Interrupts
/* disable interrupts */
/* critical section */
/* enable interrupts */

Front 41

Problems with disabling interrupts

Back 41

§ Does not guarantee mutual exclusion for multiprocessor systems (disabling interrupts across multiprocessors is expensive; message passing)
§ Limits the ability of the OS to provide timesharing
§ Could allow a process to monopolize the processor

Front 42

Lock Variables

Back 42

Use a variable to lock access to critical section

Need hardware support to guarantee an update to a lock variable cannot be interrupted
(needs to be an atomic operation )

Front 43

Problems with Lock variables approach

Back 43

•Busy waiting is employed
•Starvation is possible, because selection of next process to enter
critical section is arbitrary

Front 44

Problems with Busy Waiting

Back 44

• Very inefficient because waiting process consumes CPU cycles (depends on time to unlock, if short then busy wait is preferable to waiting with a context switch)
• Waiting process may take cycles away from
process that is holding the lock

Front 45

§ Priority Inversion for Strict Priority Scheduler

Back 45

• If busy–waiting thread has higher priority than
thread holding lock –––> no progress
§ the high priority process that busy waits never lets lower priority process finish its critical section

Front 46

Semaphores

Back 46

Integer that is accessed through two atomic operations

Front 47

Problems with semaphores

Back 47

§ A process will busy wait or spin waiting for the semaphore (this type of semaphore is also referred to as a spinlock)
§ Good when the wait time is short, context switch can be avoided
§ Bad when the wait time is long, waste CPU cycles constantly checking semaphore status

Front 48

Binary semaphore

Back 48

only two values (0, 1)

Front 49

Counting semaphore

Back 49

Used when there are a finite number of instances of some resource

Front 50

How can busy waiting be fixed?

Back 50

Changing implementation of
wait() to cause a process to block itself if the semaphore is not positive (• waiting process gets put on a waiting queue associated with the semaphore & • signal() is changed to wakeup the process at the head of the wait queue
for the semaphore)

Front 51

Process Scheduling

Back 51

Since processes are queued as they wait on a semaphore, method to determine the next process that can be employed

Front 52

Priority Inheritance

Back 52

Allow a process to inherit

the priority of a higher priority process that is
waiting until this process complete is use of a
resource

Front 53

Priority Inversion

Back 53

A lower priority process M, is able to affect the
performance of process H

Front 54

Deadlock

Back 54

A set of processes is in a deadlocked state when every process in the set is waiting for an event that can be caused only by another process in the set

Front 55

What four necessary conditions that must hold simultaneously for a deadlock to occur

Back 55

Mutual Exclusion,Hold and Wait,No Preemption,Circular Wait

Front 56

Mutual Exclusion

Back 56

a resource must be non–sharable and therefore require mutual exclusion

Front 57

Hold and Wait

Back 57

a process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes

Front 58

No Preemption

Back 58

resources cannot be preempted

Front 59

Circular Wait

Back 59

a set of waiting processes must exist such that P0 is waiting for a resource held by P1, P1 is waiting for a resource held by P2, Pn–1 is waiting for a resource held by Pn, and Pn is waiting for a resource held by P0

Front 60

Safe state

Back 60

deadlock impossible (no cycles)

Front 61

Unsafe state

Back 61

deadlock possible (cycles)

Front 62

Preemption

Back 62

temporarily interrupting a task being carried out by a computer system(interrupt)

Front 63

Bankers Algorithm

Back 63

when a new process enters a system, it must declare the maximum number of instances of each resource type that it may ever claim; clearly, that number may not exceed the total number of resources in the system. Also, when a process gets all its requested resources it must return them in a finite amount of time.

Front 64

How does Interrupt Request Line work?

Back 64

§ Sensed after executing every instruction
§ If IRL pin is active, CPU saves state and jumps to an interrupt handler

Front 65

Interrupt that can be disabled

Back 65

Maskable Interrupt

Front 66

Interrupt that cannot be disabled

Back 66

Non–Maskable Interrupt (NMI)

Front 67

What does interrupt controller do?

Back 67

Handles prioritizing and disabling interrupts

Front 68

What does the Interrupt ID from the interrupt
controller determine?

Back 68

The interrupt handler that is invoked

Front 69

What do multiple interrupt causes?

Back 69

It may share a single interrupt ID and corresponding handler

Front 70

When does a process switch occur?

Back 70

• A process voluntarily yields the CPU by waiting for an event
• A timer interrupt indicates the process’s time quantum has expired

Front 71

Scheduling Algorithm Goals

Back 71

• Maximize CPU Utilization (match ready process with an idle CPU and minimize context switch overhead)
• Maximize Throughput (number of processes
completed over a certain time period) favoring short processes would increase the throughput

Front 72

What does a process consist of?

Back 72

Alternating State 1: CPU burst & State 2: I/O burst

Front 73

How would the scheduling algorithm will schedule individual CPU bursts of a process?

Back 73

• CPU bursts are the jobs to be scheduled
• The CPU burst indicates the length of the job (the process itself does not, We make the assumption that the CPU burst length is
known)

Front 74

In which case would the process scheduler will not interrupt a CPU burst?

Back 74

In the Non–preemptive case

Front 75

What the 3 Components of the Scheduling Model?

Back 75

α – Machine Environment (Single or Multiple)
β – Constraints (e.g., Job Release Time, Job Precedent Constraints)
γ – Objective (e.g., Minimize Average Completion Time, Minimize Maximum Completion Time)

Hint 75

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Front 76

Minimize the sum of completion times

Back 76

Non–preemptive single CPU

Hint 76

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Front 77

SPT Preemptive version

Back 77

•Only scheduling processes that are in the ready queue at the same time are considered
•In reality, processes become ready at different times release times
•A preemptive version of SPT scheduling can be
constructed to handle CPU bursts of processes arriving at different times, called Shortest Remaining Processing Time (SRPT) first scheduling

Front 78

CPU Burst Length Forecasting

Back 78

The next CPU burst length of a process must be
forecasted, potentially from previous burst lengths for that process
There are many forecast models that can be used
§ Auto–regressive
§ Moving average
§ Exponential average

Front 79

Priority Scheduling

Back 79

• CPU bursts could be scheduled by priority
• For SPT the size of the burst indicates the
priority

Front 80

What problem arises when using priority scheduling?

Back 80

Starvation –––>A CPU burst with low priority could be indefinitely postponed by higher priority
processes

Front 81

How can starvation be prevented? (2 ways)

Back 81

• Perform priority scheduling on processes in the ready queue, no newly arriving higher priority process can be scheduled before an already scheduled low priority process
• Implement an aging mechanism (the age of a process influences its priority)

Front 82

Which scheduling can be implemented with a particular time quantum to place an upper bound on response time?

Back 82

Round Robin
Upper bound on response time = (n–1)q

Front 83

What does the time quantum effects?

Back 83

The upper bound on response time and the CPU utilization

Front 84

Small upper bound on response
time but decreased CPU utilization (more context switching)

Back 84

Small time quantum

Front 85

large upper bound on response
time but increased CPU utilization (less context switching)

Back 85

Large time quantum

Front 86

How should the time quantum be adjusted?

Back 86

Time quantum should be adjusted to the number of processes in the ready queue (to maintain fixed upper bound on response time)

Front 87

Multi–level Feedback Queue
Scheduling

Back 87

§ Many real operating systems maintain multi–level queues
§ Each level has its own scheduling policy
§ Processes can be moved from one queue to another

Front 88

Asymmetric Multiprocessing

Back 88

One processor is designated as master and handles all scheduling

Front 89

Symmetric Multiprocessing (SMP)

Back 89

• Each processor schedules itself
• Common ready queue
• Most popular approach

Front 90

Processor Affinity

Back 90

Processes are scheduled on the processor that they are initially assigned to

Front 91

What is the importance of load balancing?

Back 91

To increase utilization of the multiple processors

Front 92

Describe load balancing

Back 92

Processes should be moved from highly loaded
processors to lightly loaded processors on
occasion
• tradeoff with the cost of moving a process
• at odds with processor affinity

Front 93

Distributed Applications

Back 93

Applications that communicate and coordinate their actions by exchanging

messages

Front 94

Client – Server

Back 94

Kind of distributed application in which:

§ Client starts communication with server
§ Server provides information requested by client
§ Centralized: Few servers, many clients

Front 95

Peer–to–peer

Back 95

Kind of distributed application in which:

•Unstructured
§ Peers cooperate
§ Decentralized: no server coordination

Front 96

Hybrid

Back 96

Kind of distributed application in which:
Start with a client–server, create P2P

Front 97

Divide and conquer approach

Back 97

Approach used to deal with the very hostile and complex internet environment (Different transmission mediums, Different devices, Faulty systems (Noise) & Malicious entities)

Front 98

Name the 5 network protocol layers

Back 98

Application
Transport
Network
Link
Physical

Hint 98

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Front 99

Physical Layer

Back 99

Layer that:

• Codifies bits into signals (symbols)
• Decodes signals into bits
• Adds error correction

Hint 99

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Front 100

Link Layer

Back 100

Layer that handles:
• Error Correction
• Medium Access Control
• Multiple Access Control, Collision Detection
• Physical Addressing (MAC Address)

Hint 100

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Front 101

Time division multiplexing

Back 101

• A single user is allowed to transmit at a time
• Access to the whole channel capacity
(Part of MAC)

Front 102

Frequency division multiplexing

Back 102

Each user is allocated part of the available

bandwidth
(Part of MAC)

Front 103

Network layer

Back 103

Layer that handles:
• Host to host protocol
• Host Addressing
• IP address
• Packet Routing
• IP Tables

Hint 103

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Front 104

Transport layer
(• Host to host protocol)

Back 104

Layer that handles:
• Multiplexing
• Ports
• Segmentation
• Reliability
• Congestion Avoidance
• Flow control

Hint 104

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Front 105

Application Layer
(End user protocol)

Back 105

Layer that handles:
• Defines the messages exchanged between the client and the server
• Specific to the application

Hint 105

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Front 106

Sockets (Port numbers are used to address applications )

Back 106

Abstract entity that represents a

connection between two transport layer devices
§ it can also be thought of as the interface between the
transport and application layers

Front 107

Well known port numbers

Back 107

HTTP – 80

Telnet – 23
SMTP – 25

Front 108

Berkeley Sockets Interface

Back 108

Standard Application Programming Interface (API) for

sending messages over a networkGeneric API, not specific to Internet or TCP/IP Implemented by many operating systems

Hint 108

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Front 109

Stream sockets (TCP)

Back 109

TCP/IP socket type that:
• reliable service
• socket is addressed by (source IP address, source port number, destination IP address, destination port number)

Front 110

Datagram sockets (UDP)

Back 110

TCP/IP socket type that:

§ best effort service
§ socket is addressed by (destination IP address, destination port
number)

Front 111

Given n processes, how many different schedules are possible?

Back 111

f(n)= n!

Front 112

Assume i consecutive fork() statements. Express # processes as function of i

Back 112

2^i processes

Front 113

Actions taken by kernel to context switch between 2 processes

Back 113

1) OS saves state of currently executing process(ie CPU registers including program counter)

2) OS selects next process to execute

3) OS restores state of next process to execute (ie CPU registers including program counter)

Front 114

Which of the following components of program state are shared across threads in multithreaded process?

Back 114

a) Heap memory

b) Global variables

Front 115

Multiprogramming

Back 115

A process yields the CPU when it waits for I/O or terminates.

Front 116

Multitasking

Back 116

A process yields the CPU in addition to the circumstances for multiprogramming when its time quantum expires

Front 117

Difference between multiprogramming and multitasking

Back 117

Multiprogramming in intended to always keep CPU busy. Multitasking is also intended to time share the CPU among all processes.

Front 118

Five major activities of an OS with regard to process management

Back 118

1) Creating/ delete processes

2) Suspending/resuming processes

3) Scheduling processes

4) Providing mechanisms for process communication

5) Providing mechanisms for process synchornization

Front 119

Purpose of interrupts

Back 119

Interrupt the processor to handle some event, such as completion of an I/O request

Front 120

Difference between interrupt and trap?

Back 120

Trap is internally generated. Interrupt is externally generated by a pin on the CPU

Front 121

Can exception be generated intentionally by a user program?

Back 121

Yes. A process will have an instruction for this purpose.

Front 122

What is a process?

Back 122

§ A job

§ Unit of computational work § Independent fetch/decode/execute cycle

§ An executing instance of a program

§ A single stream of execution in its own address space

§ Heavyweight process

Front 123

What is a program?

Back 123

A set of instructions a computer can interpret and execute

Front 124

What the the 5 process states?

Back 124

§ New

§ Ready

§ Running

§ Waiting

§ Terminated

Front 125

Elements of process control block

Back 125

§ Process state – state of the process
§ Process number
§ Program counter
§ CPU registers
§ Memory mgmt information
§ I/O informationfUni-programming

Front 126

Uni-programming

Back 126

One process at a time, no concurrency

Front 127

Multiprogramming

Back 127

The goal is to keep the CPU busy while processes are waiting for I/O (i.e., maximize CPU utilization)

Front 128

Multitasking

Back 128

The goal is to maintain interactivity § Time sharing à like Time Division Multiplexing in Communication

Front 129

Time Sharing

Back 129

With multitasking, we can share a CPU in a computer system

Front 130

What is process scheduling?

Back 130

§ A process can run for no longer than the scheduling time “quantum”

Front 131

What happens with quantum is too small?

Back 131

Process switching overhead becomes significant

Front 132

What happens with quantum is too large?

Back 132

Interactivity suffers

Front 133

What does the ready queue consists of?

Back 133

Processes that are in memory and are immediately ready to use the CPU

Front 134

Steps for process creation/termination?

Back 134

§ Create a new process – fork()

§ Execute a new program – exec() § Wait for a process to terminate – wait()

§ Terminate a process – exit()

Front 135

When does a process become a zombie?

Back 135

When a process terminates on UNIX systems

Front 136

What happens when a process becomes a zombie?

Back 136

§ All memory is deallocated

§ PCB remains so that the parent process can read the exit status

Front 137

What happens when a parent process calls wait() to read a child’s exit status?

Back 137

The child is laid to rest

Front 138

Whats an orphan process?

Back 138

one whose parent is terminated first. [Note: orphans are adopted by the init process that will lay them to rest ]

Front 139

What are the challenges of multicore programming?

Back 139

§ Dividing activities

§ Load balancing

§ Data splitting/dependency

§ Debugging

Front 140

What is a thread?

Back 140

§ A basic unit of CPU utilization (own PC, stack and registers)

§ Shares with other threads (code section, static data and heap sections, I/O resources )

§ lightweight process

Front 141

What are the benefits of threads?

Back 141

§ Less overhead to create compared to a process

§ Shares data with other threads in the same process

§ Multi-threading is the best way to parallelize a single program execution

Front 142

What manages user threads?

Back 142

thread library

Front 143

What manages kernel threads?

Back 143

the OS

Front 144

What is a Pthread?

Back 144

POSIX standard defining an API for thread creation and implementation

Front 145

Are threads and processes synonymous in which OS?

Back 145

Linux

Front 146

What is an issue with threads?

Back 146

If a thread calls fork() should all threads be duplicated or is the new process single threaded.

Front 147

When does process work independently?

Back 147

To perform some task

Front 148

When do processes can cooperate with other processes?

Back 148

To complete some task

Front 149

What do Cooperating processes need?

Back 149

A method to communicate

Front 150

Why do threads share memory by default?

Back 150

So it is easy for them to communicate for cooperation

Front 151

What are the two methods of inter-Process communication?

Back 151

§ Message passing

§ Shared memory

Front 152

What are the advantages of shared memory IPC?

Back 152

§low overhead means high speed

§ no OS interaction, once shared memory is initialized

Front 153

What are the disadvantages of shared memory IPC?

Back 153

complex implementation for inter-computer communication

Front 154

What is Shared Memory IPC?

Back 154

A portion of memory is set aside to be shared by multiple processes

Front 155

What is message passing IPC?

Back 155

§ Alternative to shared memory

§ Communication by passing messages § send() § receive()