Concurrent and Distributed Systems

Question 1

What is a concurrent system?

Answer 1

A concurrent can (appear to) do several things at once.

Question 2

What is a distributed system?

Answer 2

A distributed system consists of a number of connected component parts (usually computer systems themselves) that are located in distinct places.

Question 3

(3 answers)

What are the motivations for concurrent and distributed systems?

Answer 3

• Convenient when modelling aspects of the real world
• Ensure efficient use or sharing of resources
• Enable improvement in the service to users

Question 4

(3 answers)

What are the benefits of concurrent systems?

Answer 4

• More responsive to the user
• More efficient use of hardware resources
• Increased speed of computation (when tasks are running in parallel)
• Better modelling of the real world

Question 5

(2 answers)

What are the drawbacks of concurrent systems?

Answer 5

• Hardware and software must be more complex
• More ways for the system to fail (e.g. deadlocks)

Question 6

(10 answers)

What are the benefits of distributed systems?

Answer 6

• Distributed systems must also be concurrent, so all the benefits of concurrent systems apply
• Enables sharing of a wide variety of resources
• Sharing may reduce the overall hardware cost of a system
• Sharing may increase the efficiency of a system by locating data and processing power close to where they are most needed
• More fault-tolerant as there are multiple possible routes for messages to travel
• Better scalability - hosts can be added or removed as required
• Interoperability
• Load balancing

Question 7

(8 answers)

What are the drawbacks to distributed systems?

Answer 7

• Hardware and software must be more complex
• Introduces new ways for the system to fail (e.g. network connection issues)
• Increased security risks due to multiple points of access
• Maintaining software on many hosts could be problematic
• If communications links fail or become faulty, some components may become unreachable
• Slow communications links may cause bottlenecks and difficulties in coordinating the system
• Distributed systems are often heterogeneous
• Impossible to completely synchronise the system so all components share the same clock time

Question 8

What is the difference between sequential, parallel and pseudo-parallel systems?

Answer 8

• Sequential systems can only execute one task at a time
• Parallel systems allow several activities to be executing at the same time
• Pseudo-parallel systems share the resource of a single processor between multiple activities, to give the impression of parallel execution - each activity runs for a short amount of time