Unit 1

Question 1

SAQ 1 - A

Which of the following system configurations are capable of being concurrent, parallel, or neither?

One processor, three activities

Answer 1

Concurrent, but not parallel – the activities can share one processor in a pseudoparallel fashion.

Question 2

SAQ 1 - B

Which of the following system configurations are capable of being concurrent, parallel, or neither?

Three processors, two activities

Answer 2

Parallel and therefore concurrent – each activity can progress simultaneously on one processor, with one idle.

Question 3

SAQ 1 - C

Which of the following system configurations are capable of being concurrent, parallel, or neither?

Three processors, five activities

Answer 3

A mixture of parallel and pseudo-parallel activity is possible here – some processes must share one or more processors.

Question 4

SAQ 1 - D

Which of the following system configurations are capable of being concurrent, parallel, or neither?

Two processors, one activity

Answer 4

No concurrency or parallelism is possible as there is only one activity – this can run on one of the processors while the other remains idle. If the activity could be split up into two or more subactivities then some concurrency and even parallelism would be possible.

Question 5

SAQ 2

Does the internet qualify as a distributed system according to the definition above (See page 20)?

Answer 5

The internet certainly satisfies the first two requirements above. Its components are computer systems – either individual computers, like PCs and web servers, or computer networks, depending on how detailed a view you take. These components are connected by computer networking and communicate using internet protocols such as TCP/IP. It is harder to say if the internet is a coherent, transparent system providing a range of functions – to naive users it may well be transparent, especially on a fast connection. At any rate, the internet is generally agreed to be a distributed system, so it must be the case!

Question 6

SAQ 3

Summarise the main benefits and costs of concurrent systems.

Answer 6

The benefits are:

• More efficient use of hardware
• Increased responsiveness to the user
• Increased speed of computation (for parallel systems)
• Better modelling of systems that interact with a concurrent real world

The costs are:

• Increased complexity of both hardware and software
• New ways for systems to fail (such as deadlock), as compared to sequential systems.

Question 7

SAQ 4

Summarise the main benefits and costs of distributed systems.

Answer 7

The benefits include

• Sharing of resources, which may be hardware, software or data.
• Scalability
• Fault-tolerance
• Interoperability – the ability of systems to work across a variety of different environments or platforms.
• Load-Balancing - if properly designed, can balance the local processing
• Centralised processing and communication activities of a system to suit the needs of the users.

The costs are:

• Introduction of new ways for the system to fail. The network connections may fail or become unreliable.
• Ensuring security may also be more difficult when there are more points of access as compared to a centralised system.
• It may also be more complex to maintain possibly different types of software on a number of hosts and to ensure that they show interoperability.

Question 8

SAQ 5

Summarise the main benefits and costs of mobile systems.

Answer 8

Pros:

• Are available from a wider variety of locations. Example: Allows linking of a laptop to local computing environment and using the local resources
• For Wireless Mobile systems, there is the benefit of avoiding the cost and disruption of fixed wiring installation

Cons:

• Increased security risk in allowing mobile users to link to a system whether wirelessly or not
• Mobile components such as laptops are more easily stolen or lost than fixed components
• Wireless communication such as radio signals are more vulnerable to interception
• Wireless communication are often lower in bandwidth than wired systems