Unit 1 From simple to complex Flashcards
Assuming that a personal computer has just one CPU, provide examples of concurrency and distribution in the everyday scenario of starting a personal computer, its startup programs, browsing the internet, using Word, printing a document, and e-mail, ppossibly downloading a large file all at the same time?
(Part 2) Concurrent activities include, downloading the large file while editing a document with Word; and printing a document while using an email program. Although these are all concurrent only are apparently concurrent rather than real as there is only on CPU.
Aspects of distribution include interactions over the internet with other systems - so sending or receiving email and possibly many intermediate computers that forward the mail data. Distrbuted systems are always potentially concurrent (and this is real concurrency) as the email server is running at the same time as the PC
Would a distributed approach to a supermarket IT system be employed for modelling reasons or for efficiency reasons?
(Part 3) It is likely to be for a blend of both.
Locating computer ssytems in each store and warehouse as well as the head office ensures that the structure of the system matches the geographical structure of the company - making it more straightforward to adapt the IT systems as new stores open.
There are efficiencies in placing as much processing as possible locally limiting data communication needed so that the bulk can happpen with head office at quieter times (like overnight.)
What are the main benefits and costs of concurrent systems?
(Part 6) The benefits are more efficient use of hardware, increased responsiveness to the user, increased speed of computation (for parallel systems) and better modelling of systems that interact with a concurrent real world.
The costs are increased complexity of both hardware and software, and new ways for systems to fail (such as deadlock), as compared to sequential systems.
What are the main benefits and costs of distributed systems?
(Part 6) The benefits include sharing of resources (hardware/software/data/etc.) and advantages in calability, fault-tolerance, interoperability and if properly designed can balance the local processing, centralised processing and communciation activities of a system to suit the needs of the users.
The costs are the 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 point of access in comparison 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.
Wireless systems are not synonymous with mobile systems, what are examples of a wireless system that is not mobile and of a wireless system that is mobile?
Fixed wireless links are often used to connect computer systems in one building to another building some distance away, possibly using a microwave or satellite dish on the roof of each building (an example of a non-mobile wireless system).
A mobile phone system has wireless components (the phones) as well as fixed components (the cell towers and other infrastructure)
Can a mobile system be “not wireless”?
(Part 6) A laptop computer can be moved around and can connect to a local network either through a wire or wirelessly. In either case it is still a mobile part of the system, so a wired laptop is an example of a mobile, non-wireless system.
What are the main benefits and costs of mobile systems?
(Part 6) The benefits are that users can communicate and access the other parts of a distributed system from a wider variety of locations. For mobile systems that are wireless there are additional benefits of avoiding the cost and disruption of fixed wiring installation.
The costs are mainly related to wireless mobile systems - there may be an increased security risk in allowing mobile users to link to a system (wirelessly or not) and mobile components can be lost or stolen more easily than fixed ones. Wireless communications are more vulnerable to interception and often are lower bandwidth than wired systems.
