10. DS contrasted with Centralised ones

Question 1

Machine =

Answer 1

Computing (processor) + Storage Resources (memory)

Question 2

Resource usage is controlled by?

Answer 2

OS

This aims to make the most efficient use possible of the resources

Question 3

OS assigns each process …? then controls how a process is granted access to…?

Answer 3

A unique identity. Address Space

OS controls a processes access to computing and storage resources.

Question 4

What is the role of the OS in a sequential, isolated process?

Answer 4

ensure no other process tampers with its data and only that process has access

Question 5

How is sequential, isolated processing bounded and limiting?

Answer 5

If a function is more computationally demanding that an single machine can cope with
If we wish to run functions concurrently (different processes) or in parallel (different processors)
If the functions are proprietary services helped in remote machines we cant hold local copies of

Question 6

Whats the main advantage of non-sequential, non-isolated processing?

Answer 6

Can switch between processes for example if one is idle and waiting for something.

Question 7

What is multiprocessing?

Answer 7

OS multitasks- allowing more than one process to be underway by controlling how it makes use of its resources.
It does this by implementing a scheduling policy which grants each active process a time source to its resources.
A group of processes is active concurrently.

Question 8

What is multiprocessing by forking?

Answer 8

A process asks the OS to make a copy of itself. This copy gets an independent copy of the parent address space. Parent can continue or wait for child to execute.

Question 9

Where is multiprocessing by forking common?

Answer 9

Client-server type Distributed Computing

Question 10

Pros and cons of multiprocessing by forking?

Answer 10

Can be expensive because of forking.
Modern OSs have strategies that make it affordable.
Safe as address spaces are distinct
Best practice is required to avoid zombie processes and unintended sharing of references to files

Question 11

What is multiprocessing by threading?

Answer 11

A process asks the OS to make a copy of itself. It assigns the same address space as the parent to the child. Parent and child may been to interact and share variables. Makes threading less expensive and less safe.

Question 12

What allows concurrent computation?

Answer 12

Multithreading

Question 13

What enables parallel computation?

Answer 13

Multiple processors

Question 14

What is a centralised system?

Answer 14

The OS ensures each process has a single address space, exclusive to it.

Question 15

What is a (seemingly) concurrent system?

Answer 15

The OS schedules the execution of n copies of a process to run in the same processor in an interleaved fashion (time slicing), typically sharing an address space

Question 16

What is a parallel system?

Answer 16

The n copies of a process each run on a different processors bound by an interconnect (i.e. a bus) or engineered as chip multi-processors. They could share a single address space

Question 17

What is a distributed system?

What about Distributed ++?

Answer 17

The n (not necessarily identical) processes each run on different machines that cannot share a single address space so must communicate.

Distributed ++: complexity reaches a point in which applications are not written against OS services. Instead they are written against middleware API