CP5 Computing June 2006

[1](a)	A printer can be connected to a computer using a cable that allows sixteen bits to be transmitted at the same time. What name is given to this type of transmission?	[1]
	parallel transmission
(b)	A mouse can be connected to a computer using a cable that allows only one bit to be transmitted at a time. What name is given to this type of transmission?	[1]
	serial transmission
(c)	Explain why a modem is required for a computer to communicate using the traditional telephone network. Explain the role of the modem.	[2]
	the telephone network uses analogue signals, computers use digital signals.. ..and a modem converts digital signals to analogue and back again.

[2](a)	In order to prevent unauthorised access to a multi-user computer system, guidelines are provided on passwords. Apart from regularly changing passwords, describe two other guidelines that users should adopt to maintain security on a multi-user computer system.	[2]
	Do not use obvious passwords such as people's names, dates of birth, pet's names etc.. Make sure the password contains a mix of upper case letters, lower case letters and digits.
(b)	Encryption is used to protect data from unauthorised users. Explain how the encrypted data can be read by an unauthorised person.	[2]
	the unauthorised person would need to know the 'key' to enable encryption... ...so he would have to hack into files where the key is stored, or get the key from an authorised person by bribery, blackmail, threats, bullying, torture or being very devious.

[3](a)	Two different types of network topologies are bus and ring.
(i)	Describe what is meant by the term data collision on a bus network and describe how a collision is detected. Briefly explain how the network deals with data collisions.	[3]
	A collision occurs when two computers send data down a bus at the same time. The network operating system detects collisions. Each computer waits a random length of time before transmitting the data again.
(ii)	Explain in detail the main features of token passing on a ring network.	[3]
	a token of data is passed from one computer to another round a network... ...the token contains data including destination computers, as well as the data being sent... ...and the receiving computer loads the token when it passes.
(b)	A wide area network uses packet switching.
(i)	Explain in detail how packet switching works.	[3]
	Data to be transmitted is split into a number of packets... ...each packet of data is transmitted through a variety of routes to the destination computer ...where it is re-assembled.
(ii)	Apart from source and destination address, give two other examples of the kind of information that would be contained in a packet.	[2]
	checksum data to make sure the received data is complete and not corrupted. information to enable the data to be re-assembled. the actual data to be transmitted. [any two]

[4]	Customers can book airline seats using the Internet. After selecting seats on one page of the website, they then move to a new page to enter their payment details.
(i)	Explain how the system stops other customers booking the same flight seats while the original customer is entering their payment details.	[1]
	the record for that particular booking is locked so other customers cannot edit it.
(ii)	Describe what the system may do to prevent a customer taking too long to enter these details.	[1]
	After a set amount of time the record editing session may be terminated and the record released to other customers.
(iii)	This system is an example of real time transaction processing. A booking file contains a record for each seat on that flight and the record is updated as soon as the seat is booked. Describe measures that should be in place to recover the booking file if it became corrupted.	[2]
	transaction log should be kept. Every transaction (booking) should have the details recorded in the log as it is made. regular backups of the booking file should be made.

[5](a)	Explain the term indexed sequential file and describe the contents of the index. Give one advantage of using an indexed sequential file over a standard sequential file.	[4]
	an indexed sequential file has records sorted in order of a primary key field... ...and it has an index that allows the computer to access a single record. ...the index contains the keys and the record addresses. The records can be processed sequentially (if all records are to be processed) or using random access (if a single record is to be processed).
(b)	Explain the term multilevel indexed sequential file and give one advantage of using a multilevel indexed sequential file rather than a random access file.	[3]
	An index may have key ranges and corresponding addresses of other indexes... A number of indexes may be accessed in turn before the record address is found. There is no need to use overflow areas.
(c)	Explain in detail how a hashing algorithm allows direct access to a record in a random access file.	[3]
	A calculation is performed on the key field... ...which results in a hash address of the record to be accessed... ...and the computer can access the record directly from the resulting hash address.
(d)	A simple hashing algorithm is one which converts a four digit input number as follows: The four digits are added together, the result is divided by 11, and the remainder of the division is used as the output from the algorithm. Calculate the output, if the input is 4275.	[1]
	4 + 2 + 7 + 5 = 18 18 / 11 = 1 remainder 7 The output is 7.

[6](a)	Briefly explain how a multi-tasking operating system manages computer memory using partitioning. Describe one consequence of the operating system failing to manage memory partitioning correctly.	[2]
	Memory (RAM) is divided into a number of partitions. When an application is run a partition is allocated to it by the operating system. If an application accesses a partition allocated to another application, then it may not run successfully and the computer may crash.
(b)	A scheduler is the part of the operating system that decides the order in which tasks are executed by the CPU.
(i)	A task can be in one of three states. In each of the following cases, name the state.
(I)	The task is waiting to be executed.	[1]
	Ready
(II)	The CPU is executing the task.	[1]
	Running
(III)	The task is waiting for a device that is in use.	[1]
	Blocked
(ii)	One method of scheduling is to take each task in turn and run that task until it has used up the allocated time slice or an interrupt occurs.
(I)	Briefly explain the term time slice and the role of interrupts in this method of scheduling.	[2]
	a time slice is a small amount of processing time that is allocated to an application. an interrupt is a signal to the CPU from a device that needs attention. Current processing is temporarily halted to allow the interrupt service routine to be run to solve the problem.
(II)	Explain how the operating system could use time slices to increase the priority of a task.	[1]
	the operating system could allocate more time slices to a job with a high priority.

[7]	A health authority has installed an expert system in local surgeries. Doctors use the system to help with the diagnosis of patients' illnesses.
(a)	Describe two benefits for the doctor and one benefit for the patient of using an expert system.	[3]
	the doctor does not have to learn and remember so much information about illnesses. the doctor does not have to be worried about making an incorrect diagnosis. the patient is assured of a reliable diagnosis using up-to-date knowledge.
(b)	Describe two parts of an expert system.	[2]
	a database of knowledge. an inference engine that uses the knowledge to make deductions about the possible diagnosis.
(c)	Describe a typical interaction that the doctor would have with the expert system when trying to reach a diagnosis.	[2]
	the doctor inputs answers to a number of questions about the patient's symptoms. the system outputs a number of possible diagnoses with possible percentage likelihoods.

[8](a)	Relational databases use primary keys and foreign keys.
(i)	Why are primary keys important?	[1]
	A primary key field uniquely identifies each record. No two records will have the same primary key field data.
(ii)	What are foreign keys and why are they used?	[2]
	key fields of other tables. Foreign fields provide the links (relationships) between the tables.
(b)	Pupils in Year 12 at a secondary school have the option of studying several subjects. It is important that the school knows: Which subjects each pupil is studying. The names of all the pupils studying a given subject. Design a three-table database for pupils, subjects and pupils studying subjects in third normal form to handle the information required for this application. You should clearly indicate the table names and any primary or foreign keys that you use.	[7]
	PUPILS(PupilID, PupilName, PupilForm) SUBJECTS(SubjectID, SubjectName) PUPILS STUDYING SUBJECTS(PupilID, SubjectID) or PUPILS STUDYING SUBJECTS(StudyID,PupilID,SubjectID) Underlined fields are primary key fields Italic fields are foreign fields.
(c)	The grade achieved by each pupil for each subject also needs to be stored. Alter your database design to accommodate this extra information (You should only show the table(s) that you change)	[1]
	PUPILS_STUDYING_SUBJECTS(PupilID, SubjectID, Grade) or PUPILS_STUDYING_SUBJECTS(StudyID,PupilID,SubjectID, Grade)

[9]	In the following question, additional credit (up to 3 marks) will be gained if your answer demonstrates skill in written communication. Powerful computers are used to model weather patterns and help make accurate weather forecasts. Atmospheric measurements are taken daily including temperature and pressure. Describe any difficulties of gathering the input required for weather forecasting and explain why analogue to digital converters would be required in this system. Explain in detail why powerful computers are essential to produce weather forecasts and why it is very difficult to produce accurate forecasts.	[7+3]
	In order to make effective forecasts, weather data needs to be collected from all areas including oceans, mountains and other inhospitable places. The data also needs to be collected 24 hours a day, every day. Some measurements such as temperature and atmospheric pressure are measured using analogue sensors, and, since computers are digital, the data needs to be converted before the computer can process it. This is done by analogue to digital converters. The data needs to be analysed by computer, comparing current data with past weather patterns, to produce weather forecasts. There are vast amounts of data coming in daily from sensors all round the world, and only the most powerful computers can deal with so much data and process it in a short length of time. It is important that the data is analysed quickly because weather forecasts need to be prepared as soon as possible. Powerful mainframes with many processors are suitable for this. The weather depends on the interplay of so many different factors, that the model is extremely complex and so weather is not easy to predict.