CP5 Computing June 2009

[1](i)	Briefly describe the difference between serial transmission and parallel transmission.	[1]
	serial - one bit of data is sent at a time down a single path parallel - many bits of data are sent at the same time down several paths
(ii)	Give one advantage of using parallel transmission.	[1]
	faster data transmission
(iii)	Explain the term multiplexing in a computer system.	[1]
	a number of signals are combined together and then sent.

[2]	Asteroid is a company that sells electrical items via their web site. The customer selects the items they want to purchase and are shown the quantity of items currently in stock. They proceed to a new web page to pay for the items. The quantity of items left in stock is then updated in the stock file and a copy of every transaction is stored in a separate file called a transaction log.
(a)	Explain how other customers can be prevented from purchasing the same stock item when the customer is paying for the items.	[1]
	the record for that stock item is locked so no purchase can be made.
(b)	Briefly describe the processing carried out on the stock file when a transaction is completed.	[1]
	the stock file is searched for the item being bought. The quantity of items in stock field is decreased by the number of items bought, and then saved back.
(c)	If the stock file becomes corrupted the company would not know how many items were left in stock. Explain in detail how the transaction log could be used to restore the corrupted stock file.	[2]
	the most recent backup of the stock file is used, ... ...and all the transactions in the transaction log since the time of the backup are processed again.

[3]	Two network administrators are discussing the merits of different types of network topologies and communication methods. One prefers a ring network using token passing while the other prefers a bus network with collision detection.
(a)	Explain in detail the main features of token passing on a ring network and give one reason why the first administrator may prefer this method of network communication.	[4]
	a transmitting computer attaches data to a token that passes round the network... ...the token has the address of the receiving computer and is passed round the ring from one computer to another... ...until the receiving computer receives the token and loads the data. Greater reliability - less chance of data failing to get to the destination due to data collisions
(b)	Describe what is meant by the term data collision on a bus network and describe how a data collision is detected. Briefly explain how the network deals with data collisions. Give one reason why the second administrator may prefer this type of network topology.	[4]
	if two computers transmit data down the same path at the same time a data collision occurs. transmitting computer will listen on the network to see if another computer transmits data at the same time. if a collision occurs, the transmitting computers will each wait a random amount of time before sending the data again. cabling costs are less.

[4](i)	Random access files use a hashing algorithm and an overflow area.
(a)	State the purpose of a hashing algorithm.	[1]
	a calculation on the key field of a record, that results in the address of the block where the record is stored.
(b)	State the purpose of an overflow area.	[1]
	when storing a new record, if the hashing algorithm results in a block that is full, the record is stored in an overflow area.
(c)	Explain how a record is located if it is in the overflow area.	[2]
	the hashing algorithm results in the hash address of the block where the record should be stored. The computer searches this block. If it does not find the record, there will be a pointer to an overflow area where the record is stored.
(ii)	Indexed sequential files use indexes to locate records.
(a)	Describe the contents of an index.	[2]
	the index will consist of key fields ..and addresses.
(b)	Explain how a three level index system is used to access a record in a multilevel index sequential file.	[3]
	a search through the first level index for the range in which the record's key field falls will result in the address of the second level index... a search through the second level index for the range in which the key field falls will result in the address of a third level index... ...a search through the third level index will result in the actual address where the record is stored.

[5]	A wide area network uses packet switching. Explain in detail how packet switching works and give one example of data that would be contained in a packet.	[4]
	data to be transmitted is split into a number of discrete packets of data each packet is sent separately down the network being passed on from one computer to another - each packet may take a different route through the network. packets are re-assembled at the destination computer data in the packet may be the source address, destination address, reassembly information.

[6]	A multi-user operating system uses interrupts, time slices and partitioning.
(a)	State what is meant by the term interrupt and give examples of two conditions or events that could generate an interrupt.	[3]
	an interrupt is a signal to the CPU requesting attention. a malfunctioning hardware device may send an interrupt a software error (eg division by zero) may generate an interrupt.
(b)	Describe the term time slice and briefly describe how the operating system uses time slices to allocate processor time.	[2]
	a time slice is a small amount of processing time the operating system will allocate time slices to each user in turn. It will also allocate a priority to each user. The users with the highest priority will be processed first.
(c)	Describe the term partitioning and briefly describe how the operating system uses partitioning to allocate main memory.	[2]
	the memory is divided into discrete partitions... ... each of which is allocated to a different task. The task may only use its allocated partition of memory.

[7](i)	Briefly describe the term distributed processing.	[1]
	processing is shared between a number of different computers.
(ii)	Describe one advantage of using this type of processing.	[1]
	processing is completed faster.

[8]	A garage has installed an expert system to help the mechanics identify faults on cars.
(a)	Describe two parts of an expert system.	[2]
	a database of car faults an inference engine - a set of rules for making deductions about what the car fault might be.
(b)	Outline a typical interaction that a mechanic would have with the expert system when trying to identify a fault.	[2]
	input the symptoms the car is showing output the possible faults and the ways of fixing them.

[9](a)	Explain the difference between a primary key and a foreign key in a relational database, and explain the purpose of a foreign key.	[3]
	primary key - uniquely identifies each record in a table foreign key - primary key field of another table ...provides a relational link between records in different tables.
(b)	Explain what is meant by the terms data redundancy and data inconsistency in a database.	[2]
	data redundancy - the same data is stored more than once in a database. data inconsistency - there may be differences in two copies of the same data.
(c)(i)	Every September a college enrols many students on one or more courses. Each course has one teacher who may also be a teacher for other courses. The college need to know which courses a student is studying, and all the students studying any given course. It also needs to know which courses a teacher teaches. Design a four-table database in third normal form to handle the information required for this application. Where appropriate you should include primary and foreign keys and other additional relevant fields in each table. You should also use meaningful table names and clearly indicate any primary or foreign keys that you use.	[10]
	STUDENTS(StudentID, StudentName, Address, DOB) COURSES(CourseID, CourseName, CourseDate, TeacherID) TEACHERS(TeacherID, TeacherName) STUDENT_COURSES(StudentID, CourseID) Primary keys are underlined Foreign keys NB: STUDENT_COURSES table has a compound primary key field consisting of two fields.
(ii)	Each student achieves one overall grade for each course. The teachers would like to store this grade in the database. Amend your database design to store this grade. You only need to show amended table(s).	[1]
	STUDENT_COURSES(StudentID, CourseID, Grade)

[10]	Sensitive personal data stored in an electronic format is frequently transferred between different departments of large organisations.
(a)	Briefly describe why it would be sensible to encrypt this data.	[1]
	If the data got into unauthorised hands, then it would be meaningless if it was encrypted.
(b)	Explain how encrypted data can be read by the appropriate person.	[1]
	The appropriate person is the only person who has a 'key' which can be used to decrypt the data.

[11]	In the following question, additional credit (up to 3 marks) will be given if your answer demonstrates skill in written communication.
	Car manufacturers have been using computer controlled robots to help build motor cars for many years. Describe in detail the effect that using computer controlled robots to help build motor cars has had on the quality of the cars produced. Describe the cost benefits for the car manufacturers. The introduction of the computer controlled robots has had a significant effect on the health and safety of the workforce and employment within car manufacturing companies. Describe in detail the effects on the workforce and on employment.	[8+3]
	The quality of cars built by robots will have improved because robots are able to work to very precise specifications. The consistency of quality will also be better as robots can repeat exactly the same movements every time. Despite the initial cost of purchasing and installing the robots, money will be saved because robots can work 24/7 without needing to be paid a wage like a human worker. The workforce do not need to work in hazardous environments. The robots can operate in rooms filled with paint spray, where humans would suffer from the fumes. Lifting heavy car parts would not be a problem for robots, but may cause back problems or muscle injuries to humans. The types of job in the car manufacturing industry have changed. Many of the human workers have been replaced by robots,... ... but new jobs have been created, such as computer operators/programmers, and robot maintenance. Many workers would have been re-trained for the new jobs.