CP5 Computing June 2005

1.	The Internet contains a large number of web pages. Describe two ways that users of the Internet are able to move to specific web pages.	[2]
	Enter the URL of the web page in the address box of the browser. Click on a hyperlink to that web page.

2(a)	Data can be transmitted through a wide area network using packet switching or circuit switching.
	(i) Explain in detail how circuit switching works.	[2]
	A number of switches are turned on ... ...to create a circuit down which data can be transmitted.
	(ii) Explain in detail how packet switching works.	[3]
	Data to be transmitted is split into packets. Each packet contains an address on the network where the data is to be sent. Routers send the packets of data down the network to their destination where they are re-assembled.
	(iii) State one reason why packet switching may be preferred.	[1]
	A more reliable system because a fault in the network may still allow data to be transmitted.
(b)	Data collisions can occur in some networks.
	(i) Explain the term data collision and explain how the network detects a data collision.	[2]
	If two computers send data down the same bus at the same time, a data collision occurs. Collisions are detected by the hardware that is sending the data.
	(ii) Briefly explain how the network deals with a data collision.	[1]
	A check is made to see if a bus is clear before data is transmitted.

3. (a)	Two functions of a multi-user operating system are to manage the processor and manage memory.
	(i) Explain in detail how the operating system uses time slicing to allocate processor time to tasks.	[2]
	Small amounts of processing time are allocated by the operating system to each task in turn. Tasks are selected using a system of priorities. The higher priority tasks receive more time slices of processing.
	(ii) Explain in detail the term partitioning when used to allocate main memory	[2]
	A partition is an area of memory allocated to a task. No other task can use that area of memory. Each task is allocated memory when it is loaded and workspace when it is being processed.
(b)	The operating system has to deal with interrupts.
	(i) What is a computer interrupt?	[1]
	A signal sent to the CPU from a device that needs some attention.
	(ii) The operating system is carrying out a task when an interrupt is generated. Explain in detail the sequence of events following the interrupt.	[3]
	The processor stops the task it is currently doing, and saves the values of all the registers. The operating system then runs an interrupt service routine to deal with the problem. When finished, the processor loads back the saved register values and carries on with its original task.

4. (a)	Random access files use a hashing algorithm and an overflow area.
	(i) Assuming the overflow area is not required explain how a record is located using a hashing algorithm.	[2]
	A hashing algorithm is a calculation performed on the key field of a record... ...which results in the address of a block where the record is stored.
	(ii) Assuming the overflow area is required, explain how a record is located.	[2]
	The hashing algorithm results in the address of a block. When that block is accessed, the records are serially checked for the record required. If it is not found there, then the corresponding overflow area is checked to find the record.
(b)	Explain the term indexed sequential file.	[2]
	The file is sequential - stored in sorted order of a key field. The file also has an index which allows the computer to find the address of a single record by looking up its key.
(c)	Explain how the indexes are used to access a record in a multilevel index sequential file with a three level index.	[3]
	Index 1 is searched for the required key. This index results in the identity of Index 2. Index 2 is searched for the key, and this results in the identity of Index 3. Index 3 is searched which results in the address of the record required.

5. (a)	A government office stores information about members of the public on a computerised system. Certain government employees are allowed to view and amend this information and several employees may access the same record simultaneously.
	(i) Why should the system prevent two employees updating the same record simultaneously.	[1]
	If employee A edits the record at the same time as employee B, and A saves the edited record before B, the changes B made will overwrite the changes A made which will then be lost.
	(ii) Explain how the system prevents two employees updating the same record simultaneously.	[1]
	The record will be locked when employee A opens it for editing. This will prevent employee B from editing the record. When A saves the changes, the record is then unlocked.
(b)	Members of the public may be concerned about government employees accessing and amending their confidential information.
	(i) Describe two methods of ensuring that only authorised employees can access the information.	[2]
	A system of passwords will allow only authorised employees to access the data. Different security levels may be allocated to employees. Only those with a given security level may be allowed to access the data. A firewall system may be set up to prevent unauthorised access from other networks.
	(ii) Describe in detail how an employee who had misused this confidential information could be identified.	[2]
	A log may be kept of when users logged in to use the network, and the times they logged out. When data is accessed or changed, the time and date is recorded in the database.

6.	A dental surgery stores patients' dental records and patients' appointments on a personal computer's hard disc.
(a)	Describe two procedures that could be implemented to minimise data loss in the event of hard disc failure.	[2]
	Regular backups of the data should be made onto another medium. The backup should be stored in a different place to the original data. Hard copy of the data could be printed.
(b)	Other than hard disc failure, describe an event that could result in the loss of data.	[1]
	A virus may be introduced to the computer which deletes the data on the hard disc.

7.	A supermarket has a large computer at head office. Each store has a computer that is connected to the head office computer. Some data are stored and processed locally at each store and other data are stored and processed at head office.
(a)	What is the name given to this type of system, where data are stored and processed at more than one location?	[1]
	Distributed system.
(b)	State one advantage of processing data in this way.	[1]
	Improved performance of the system because one computer is not overloaded with processing.

8. (a)	Some devices use analogue signals; other devices use digital signals.
	(i) Explain the term analogue signal.	[1]
	Values can lie within a continuous range of numbers.
	(ii) Explain the term digital signal.	[1]
	Values can only be a distinct set of numbers.
(b)	Different data transmission methods are available. State the name of each method described below.
	(i) Data is transmitted in both directions at the same time.	[1]
	Duplex.
	(ii) Data is transmitted on one direction only.	[1]
	Simplex.

9.	Why do the computers used in the production of animated films need to be so powerful?	[2]
	The amount of data in a picture is large. Animations consist of many pictures so the volume of data needed to be processed is very large. If the computer were not powerful, the processing of the data would take a very long time.

10 (a)	What are foreign keys and how are they used in a relational database?	[2]
	A key field of another table. They are used to provide links (relationships) between entities (tables).
(b)	A holiday car rental company rents cars to customers. It is important to keep a record of all rentals. Design a three-table database in third normal form to handle the information required for this application. Each table should only include relevant information. You should clearly indicate the table names and any primary or foreign keys that you use.	[8]
	CARS(Car_ID, Car Make, Car Model, Car Registration) CUSTOMERS(Customer_ID, Customer Name, Customer Address) RENTALS(Rental_ID,Customer_ID, Car_ID, Rental Date) Underlined fields are key fields. Italic fields are foreign fields.

11. (a)	Databases often use query languages and data dictionaries.
	(i) what is a query language?	[1]
	A language that allows search criteria to be specified for queries in a database.
	(ii) what is the purpose of a data dictionary?	[1]
	To store details about the data such as the field names and types in each table.
(b)	Explain what is meant by data being in first normal form.	[1]
	There are no repeating groups of records.

12.	In the following question, additional credit (up to 3 marks) will be given if your answer demonstrates skill in written communication. A company that manufactures a range of steel products, for example small precision screws, has automated its production lines and installed robotic machinery. Describe the effect that automating the production process is likely to have had on: the quality of the steel products manufactured the cost benefits for the company the health and safety of the workforce employment within the company.	[9+3]
	An automated production process will mean more consistent quality of products. The production process can operate without interruption for 24 hours a day every day. This will mean increased production and will generate more money for the company. The company will have to pay for the cost and installation of the robotic machinery but will save money because they will not need to pay wages to the workers that have been replaced. The robotic machinery will replace employees with dangerous jobs or where there is a health risk such as paint fumes. The robots are able to operate under these conditions and this will mean a better environment for the workforce. There may be some redundancies because the robots will replace workers on the production lines. However, new jobs will also be created such as robot maintenance or programmers. There may be better to retrain some of the workforce rather than make them redundant.