UNIT 1 Flashcards
1-1a Can this system configuration be concurrent, parallel, or neither? : One processor, three activities
Concurrent, but not parallel
– the activities can share one processor in a pseudoparallel fashion
1-1b Can this system configuration be concurrent, parallel, or neither? : Three processors, two activities
Parallel and therefore concurrent
– each activity can progress simultaneously on one processor, with one idle.
1-1c Can this system configuration be concurrent, parallel, or neither? : Three processors, five activities
A mixture of parallel and pseudo-parallel activity is possible here
– some processes must share one or more processors
1-1d Can this system configuration be concurrent, parallel, or neither? : Two processors, one activity
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.
1-2 How is a distributed system generally defined, and does the internet qualify as a distributed system?
-
1) Contains a number of distinct computer systems at different locations
- Yes, Internet components are computer systems like PCs and web servers, or computer networks.
2) Distinct components can communicate with one another using a variety of communication technologies over some sort of network..
- Yes. Internet components are connected by computer networking and communicate using internet protocols such as TCP/IP.
3) Should appear to its users as a single coherent system providing a range of functions.
- Yes, for naive users, but it is harder to say if the internet is really a coherent, transparent system providing a range of functions. However, the internet is generally agreed to be a distributed system.
1-3a Summarise the main benefits of concurrent systems.
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
1-4a Summarise the main benefits of distributed systems.
The benefits include:
- sharing of resources, which may be hardware, software or data.
- advantages in scalability, fault-tolerance, and interoperability,
- can balance the local processing, centralised processing and communication activities of a system to suit the needs of the users.
1-5a Summarise the main benefits of mobile systems.
The benefits are:
- users can communicate and access the other parts of a distributed system from a wider variety of locations.
- eg, linking a laptop computer to a local computing environment allows users to use their personal computing facilities and any data stored there as well as using local facilities such as printers, scanners or file servers.
- For mobile systems that are wireless there are additional benefits of avoiding the cost and disruption of fixed wiring installation.
1-6 Draw a diagram to show how each of the following categories of computer system is distinct from, includes, or overlaps with the others.
Sequential
Concurrent
Distributed
Mobile
Here, ‘mobile’ means a system with at least some mobile components (like a mobile phone system which includes fixed hardware as well as the mobile handsets).
- the sets for sequential and concurrent systems have no overlap.
- all distributed systems are (potentially) concurrent,
- mobile systems may be distributed or could be independent (like a PDA). Independent mobile systems are likely to be concurrent nowadays, depending on their hardware and software design.
- The diagram is shown in Unit 1, Figure 11
1-3b Summarise the main costs of concurrent systems.
The costs are:
- increased complexity of both hardware and software,
- new ways for systems to fail (such as deadlock), as compared to sequential systems.
1-4b Summarise the main costs of distributed systems.
The costs are:
- new ways for the system to fail – the network connections may fail or become unreliable.
- security may be more difficult when there are more points of access,
- more complex to maintain and ensure interoperability., with possibly different types of software on a number of hosts
1-5b Summarise the main costs of mobile systems.
The costs are mainly, but not entirely, related to wireless mobile systems.
- 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 communications such as radio signals are more vulnerable to interception and often are lower in bandwidth than wired systems.
- These drawbacks can be overcome, for example by encryption or by better hardware, but these have their own associated costs.
