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Computers and the Internet > Week 1 > Flashcards

Week 1 Flashcards

1
Q

What is an OS?

A

An OS is a software that manages computer resources and offers abstractions

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2
Q

What is the Kernel?

A

Central part of OS

Runs all time on the computer

Functionality depends on OS design

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3
Q

What is the Kernel Mode? (Or privileged mode)

A

Where the kernel runs

CPU has full access to system resources

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4
Q

What is User Mode?

A

It’s where applications run

CPU has restricted access to system resources

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5
Q

How does the OS switch between kernel and user mode

A

To switch to kernel mode the trap mode bit is triggered and set to 0, after the task has been performed in kernel mode the return mode bit is set to 1 which brings it back to OS

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6
Q

What is a Monolithic Structure?

A

Large kernel with most of OS services run in kernel mode

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7
Q

What are the pros and cons of a monolithic structure?

A

Pros:

Fast performance

Cons:

Stability and Security

Maintenance and Debugging

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8
Q

What is are the pros and cons of a Microkernel Structure?

A

Pros:

Stability and Security

Cons:

Poor Performance

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9
Q

What are the pros and cons of a Microkernel Structure?

A

Pros:

Stability and Security

Cons:

Poor Performance

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10
Q

What is a Layered Structure?

A

OS broken into hierarchy layers

Communication with above and below

Implemented into computer networks (TCP/IP)

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11
Q

What are the pros and cons of a Layered Structure?

A

Pros:

Easy to maintain debug and test

Security and Stability

Cons:

Poor performance

Design challenges

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12
Q

What is a Modular Structure?

A

Combines aspects of Monolithic and Microkernels

Start with small kernel

additional services are loaded on demand via modules

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13
Q

What are the pros and cons of a Modular Structure?

A

Pros:

Fast Performance

Flexibility and Extensibility

Cons:

Monolithic as more modules loaded

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14
Q

Fact

A

OS’s combine different structures

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15
Q

What is a file?

A

A file is a named collection of related data stored on non-volatile storage

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16
Q

What are magic numbers in files?

A

Sequence of bytes at beginning of file

17
Q

What are examples of meta data?:

A

Name

Identifier

Type

Location

Size

Timestamps

Permissions

18
Q

Where is Meta Data stored in linux?

A

In an Inode

19
Q

What are the 2 features of Linux Files?

A

Everything is a file

Files represented by tree-like inode pointer structures

20
Q

What are some examples of Linux file types?

A

Regular files

Special files (character of block)

Directories

Pipes

Links (soft or hard)

21
Q

What is a hard link?

A

Another name for an existing file

points directly to inode of file

If file is moved/deleted the link will still work

22
Q

what is a soft link?

A

A pointer to filename

If file is moved/deleted, the link will not work

23
Q

How is the storage space divided for files?

A

Filesystems divide storage space into fixed-size blocks

Typical block size is 4096 bytes (4KB)

24
Q

What can a file be broken down into?

A

into chunks that fit into blocks

25
Q

What are magnetic disks?

A

Use magnetic fields to store data

eg. HDD or floppy disks

26
Q

What are magnetic disks organised into?

A

Platters - Circular disks

Read/Write Heads

For reading and writing the head senses/ changes the magnetism of a sector

At bit level: magnetism in one direction represents a 1

magnetism in other direction represents a 0

27
Q

How are the platters of a Magnetic Disk organised?

A

Each platter is divided into circular tracks

Each track is divided into sectors - each sector has fixed size

Set of all tracks are immediately above one another make up a cylinder

28
Q

How does a magnetic disk work?

A

Read/ Written by moving the arms in and out of required cylinder

All heads/ arms move together

Platters rotate; rotation speed is related to data transfer rate

29
Q

What is a Solid State Disk?

A

No moving parts and instead stores data using flash memory

30
Q

What are the components in an SSD?

A

Controller (embedded processor)

Buffer memory (volatile memory)

Flash Memory - divided into pages that are grouped into blocks

31
Q

What are the read, write and erase speeds of an SSD?

A

Read - Fast

Write to empty drive - Fast

Erase - Slow

32
Q

How is an SSD read?

A
  1. Copying flash memory page into the buffer
  2. Reading data from the page in the buffer
33
Q

How is an SSD overwritten?

A
  1. Copying memory block into buffer
  2. Erasing block in the flash memory
  3. Modifying block in the buffer
  4. Writing block from the buffer to the flash memory
34
Q

What are the Pros and Cons of SSDs compared to magnetic?:

A

Pros:

SSDs are faster

SSDs more reliable

SSDs are more power efficient

Cons:

SSDs more expensive

SSDs deteriorate with every write

35
Q

What is a wear levelling?

A

A process that is designed to extend the life of solid state devices

36
Q

What is dynamic wear levelling?

A

New data written to least-recently-used block

Avoid wearing out certain blocks by writing to the same ones again and again

problem: “cold” data is not moved

37
Q

What is Static-wear-levelling?

A

Same as dynamic besides:

Periodically moves existing data to least-recently-used block

Therefore we avoid wearing out certain blocks while blocks with cold data is never moved

38
Q

What is the benefit of wear levelling?

A

A block will fail once it reaches a critical amount of writes

Thanks to wear-levelling, we spread the writes evenly among the blocks

Computers and the Internet (10 decks)

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