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Computers and the Internet > Week 3 > Flashcards

Week 3 Flashcards

1
Q

What is a process scheduler (allocates CPU time)?

A

Allocates CPU time to various processes

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2
Q

What are the 4 Scheduling Algorithms?

A

First Come First Served (FCFS)

Round Robin (RR)

Shortest Process Next (SPN)

Multilevel Queueing

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3
Q

What is First Come First Served (FCFS)?

A

Processes get executed in order they arrive

Not interrupted until finishes or reaches a wait state

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4
Q

What are the Pros and Cons of FCFS?

A

Pros:

Simple and easy to implement

Reduced context switching

Intuitively fair

No starvation

Cons:

Convoy effect - Long waiting time, poor responsiveness

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5
Q

What is Round Robin (RR)?

A

allocates each task an equal share of the CPU time

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6
Q

What are the pros and cons of RR?

A

Pros:

Fair CPU Allocation

Responsiveness

No starvation

Cons:

Time quantum sensitivity

Context switch overhead

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7
Q

What is Shortest Process Next (SPN)?

A

Select the process with the shortest execution time

Non Preemptive - something cannot be taken away or interrupted

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8
Q

What are the pros and cons of SPN?

A

Pros:

Better average waiting time

Responsiveness

Cons:

Estimating process execution time

May lead to starvation

Longer processes wait longer

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9
Q

What is Multilevel Queueing?

A

a CPU scheduling algorithm

divides a ready queue into multiple smaller queues

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10
Q

What is Fixed-Priority Scheduling?

A

High priority queues are executed first

May lead to starvation

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11
Q

What is Time Slicing?

A

A time slice for each queue

Eg. 60% for interactive, 30% system, 10% batch

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12
Q

What are the pros and cons of Multilevel queueing?

A

Pros:

Supports different performance objectives

Cons:

Complex and difficult to calibrate

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13
Q

What is a multi core processor?

A

A multi-core processor has multiple processing units (cores) on a single CPU chip

Each core has its own L1 cache memory

There is a cache hierarchy

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14
Q

What is the common queue?

A

When a processor becomes available, it chooses a new process from a common queue

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15
Q

What are private queues?

A

When a processor becomes available, it chooses a new process from its private queue

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16
Q

What are the 2 methods for efficient Multi-Processor Scheduling?

A

Load Balancing

Processor Affinity

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17
Q

What is Load Balancing?

A

Evenly distribute processes among CPU cores

Common ready queues automatically enforce load balancing

18
Q

What is Processor Affinity?

A

Keep a process on the same CPU core(s)

Soft affinity: only move processes if there is a good reason

Private queues automatically enforce processor affinity

19
Q

What is The Linux Scheduler?

A

A multi-queue scheduler

Scheduling domain: a set of CPU cores than can be balanced against each other

Bottom-up Load balancing among domains

Processor affinity - only perform load balancing if there are severe imbalances

20
Q

What is monoprogramming (single, single)?

A

Running a single program at a time within a single address space

21
Q

What is multiprogramming?

A

allows multiple programs to run simultaneously on a single CPU

basic form of parallel processing

22
Q

What are the 3 Memory Management Tasks?

A

Relocation

Protection

Sharing

23
Q

What is Relocation(hint: new location in m)?

A

Moving a process to a new location in memory without disrupting its execution

24
Q

What is Protection?

A

User processes need to be protected from each other

System processes should be protected from user’s processes

25
Q

What is Sharing (processes may)?

A

Processes may sometimes need to share data

26
Q

What is (Fixed/Static) Partitioning?

A

Memory is divided into partitions of fixed boundaries (equal or unequal sizes)

1-1 mapping of partitions and processes

27
Q

What are the pros and cons of Fixed Partitioning?

A

Pros:

Easy to understand or implement

No external fragmentation

Cons:

Internal fragmentation

Limited by number and size of partitions

28
Q

What is Dynamic Partitioning?

A

Exact memory allocation - only what is needed

Partitions of variable length and number

1-1 mapping

Starts well then leads to external fragmentation

29
Q

What is External Fragmentation?

A

Space is wasted between partitions

30
Q

What is Compaction?

A

combining all the empty spaces together and processes

Fixes external fragmentation

31
Q

What are the pros and cons of Dynamic Partitioning?

A

Pros:

No internal fragmentation

More efficient than static partitioning

Cons:

External fragmentation

Overhead of compaction

32
Q

What is Simple Segmentation?

A

Process divided into segments

Segments loaded into memory

Segments do not need to be contiguous

33
Q

What are the pros and cons of Simple Segmentation?

A

Pros:

Sharing and Protection

Better handling of larger programs

No internal fragmentation

Cons:

External fragmentation (< dynamic)

34
Q

What is Virtual Memory Segmentation?

A

Segmentation + Virtual memory

Segments can be swapped between memory and disk storage

OS loads segments into memory as needed

35
Q

What is virtual memory?

A

Use of disk space to extend main memory; illusion of larger memory but much slower

36
Q

What are the pros and cons of Virtual Memory Segmentation?

A

Pros:

Can fit processes larger than memory

Cons:

More complex memory management

37
Q

What is Simple Paging?

A

Memory divided into equal fixed-size frames

Process is divided into same-size pages

38
Q

What are the pros and cons of Simple Paging?

A

Pros:

No external fragmentation

Simple memory allocation

Cons:

Small internal fragmentation

Page tables can become large

39
Q

What is Virtual Memory Paging?

A

Paging + Virtual memory

Pages loaded into frames as in simple paging, except that not all pages need to be loaded at same time

40
Q

What are the Pros and Cons of Virtual Memory Paging?

A

Pros:

Can fit processes larger than memory

Cons:

adds complexity (overhead)

41
Q

Protection & Sharing with Segmentation and Paging

A

Goals:
Protection: Each process can only access its own pages/segments
Sharing: Multiple processes can access the same page/segment
Implementation:
Each frame/segment has a number of protection bits specifying
read, write, execute permissions, which processes have these permissions
Protection/sharing is generally easier with segmentation than with paging since
Segment table is smaller than the page table
Segments are more natural units for protection/sharing

Computers and the Internet (10 decks)

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