CP5 Paper Computing 2007

[1](a)

A buffer is used when data is entered via a keyboard into the computer.

(i)

Explain the role of this buffer.

[1]

the buffer is an area of memory where data input from the keyboard is collected. When the buffer is full, the data is sent to the CPU.

(ii)

Why is the buffer required?

[1]

input from a keyboard is slow compared to the speed of the processor.

(b)

Explain double buffering and give an advantage over single buffering.

[2]

two buffers are used - one is emptied as the other is filled.
speeds up the process of data transfer

[2]

A football club allows seats to be booked over the telephone. Telephone calls are handled by several sales assistants. As each seat is booked a sales assistant types the details into a computerised real-time transaction processing system. A record in the booking file is updated to indicate that the seat has been booked and a copy of the booking is stored in a transaction log.

(i)

Describe how the system prevents a seat being booked twice.

[2]

when a seat booking is made, the record is opened and locked so it cannot be edited by another assistant
when the booking has been made, the record is immediately updated, saved and unlocked.

(ii)

Following a system failure, the booking file is damaged and the booking data lost. Explain how this transaction log could be used to restore the booking file.

[1]

a backup of the data from before the time of the system failure is loaded, and all transactions from the time of the backup are repeated.

(iii)

Other than name, address and telephone number, give two other fields you would expect to find in a transaction log record.

[1]

fixture date,
seat number

[3](a)

Explain why networks require protocols.

[1]

without a protocol one computer on the network would not be able to interpret data it received from another computer.

(b)

Describe in detail:

(i)

token passing (within a ring network)

[3]

the sending computer attaches a message to a token,
...which also contains the address of the computer to which data is to be sent
the token is passed around the network, each computer passing it on to the next
..until the receiving computer detaches the message from the token

(ii)

data collisions and their detection (within a bus network).

[3]

data collisions occur when two computers try to send data at the same time
stations on the network listen out for data collisions
if they occur, the computers wait a random amount of time before sending the data again

(c)

Name the device that is required to link two dissimilar computer networks.

[1]

a gateway

[4]

Operating systems use interrupts to manage tasks.

(i)

A task can be in one of three states: ready, running or blocked. Briefly describe each of these states.

[3]

ready - a task is waiting to be executed
running - the task is being executed by the CPU
blocked - the task is put on hold while using a device and cannot be executed until finished

(ii)

What is a computer interrupt?

[1]

a signal generated by a device that requires attention

(iii)

Give two examples of computer interrupts.

[2]

a printer that has run out of paper may generate an interrupt
<CTRL><ALT><DEL> to reboot a computer
an interrupt to indicate the end of a time slice of processing time

(iv)

The operating system is processing an interrupt when another interrupt with a higher priority is generated. Explain in detail the sequence of events following the second higher priority interrupt.

[3]

the processing of the interrupt halts and the environment is saved.
the higher priority interrupt is serviced and when finished...
...the servicing of the original interrupt is completed

[5](a)

The following diagram is a simplified example of a multi-level index for an indexed sequential file with three levels of indexes.

Explain in detail how each of the indexes is used to locate the record with a key value of 4183.

[3]

Main Index
Range of Key Values	Index number
0000-2499	01
2500-4999	02
5000-7499	03
7500-9999	04

Index 02
Range of Key Values	Index number
2500-2999	021
3000-3499	022
3500-3999	023
4000-4499	024
4500-4999	025

Index 024
Range of Key Values	Index number
4000-4099	block 169
4100-4199	block 170
4200-4299	block 171
4300-4399	block 172
4400-4499	block 173

the Main Index is accessed. The ranges of key values are serially checked for the range containing the key 4183. The Index number 02 is found....
...so Index 02 is accessed. A serial search of the ranges finds that the range containing the key 4183 is 4000-4499. The corresponding Index number is 024...
..so Index 024 is accessed. A serial search of the ranges tells the computer that the record 4183 is in the range 4100-4199 so can be found in block 170.

(b)

Random access files use a hashing algorithm and an overflow area.

Explain in detail how a record is located using a hashing algorithm when the record is stored in the overflow area.

[4]

the hashing algorithm is performed on the key field value...
resulting in a hash address - the block of data where the record should be stored.
a serial search of records in that block fails to find the record, so the address of the overflow area is accessed...
and a serial search of the overflow area should find the record.

[6](a)

The table below shows some data stored in an un-normalised database for products and their suppliers.

Product Description	Product Cost	Quantity In Stock	Supplier Name	Supplier Contact	Tel Num
Garden Bench	£100	9	Wood Benches Direct	Mr Brown	033 345 876
Large Garden Shed	£250	5	Forest Supplies	Ms Lloyd	088 231 786
Patio Seating Set	£500	12	Garden Furniture Company	Mrs Jones	065 231 874
Large Umbrella	£50	17	Garden Furniture Comany	Mrs Jones	065 231 874
Small Garden Shed	£150	3	Forest Supplies	Ms Lloyd	088 231 786
Outdoor Heater	£300	14	Garden Furniture Company	Mrs Jones	065 231 874
.................	........		....................	.........

Explain what is meant by the term data inconsistency, giving one example from the above table.

[2]

data stored in more than one place may not be identical.
Eg. In the above table, 'Garden Furniture Company' is stored three places...however, one of them is mis-spelled 'Garden Furniture Comany'

(b)

Explain what is meant by data being in first normal form.

[1]

a database is in first normal form if there are no repeating groups. (Every field has only one item of data in it.)

[7]

A government is proposing to build a new motorway that will allow cars to be controlled by computer systems with minimal intervention from the driver. Each car will be fitted with appropriate sensors which will ensure that it can travel safely on the motorway.

(i)

Describe two uses of feed-back in this system.

[2]

a sensor will detect if the car is deviating from the lane and send a signal to correct the steering...repeatedly until the car is back in the lane
a sensor will detect when a car is getting too near another car and send a signal to the braking system...repeatedly until the car is a safe distance back.

(ii)

Describe two safety features that should be included in this type of system.

[2]

a second computer in the car that can take over immediately if the main computer breaks down.
at least two sensors for each task in case of a sensor failure

[8](a)

Data can be transmitted using simplex and full duplex.

(i)

Explain what is meant by the term simplex.

[1]

data can only be sent in one direction

(ii)

Explain what is meant by the term full duplex.

[1]

data can be sent in both directions at the same time

(b)

Explain the role of a multiplexor in a computer system.

[1]

allows more than one data signal to travel at the same time

(c)

Using an example, describe the term distributed system.

[2]

several computers may be linked together

[9](a)

In addition to a microphone, explain what hardware is required to input speech into a computer.

[1]

an analogue-to-digital converter

(b)

Explain why this hardware is required.

[1]

speech produces an analogue signal, but computers can only process digital data

[10](a)

Explain the roles of primary keys and foreign keys in a relational database.

[2]

a primary key is a field that uniquely identifies each record.
a foreign key is a field of a table that is the primary key of another table. Foreign keys provide links between tables of data.

(b)(i)

A surgery has several doctors and many patients. Each patient can make one or more appointments with a doctor.

The surgery receptionist records which patient has made an appointment with which doctor and the time and date of the appointment.

Design a three-table database in third normal form to handle the information required for this application. Each table should include only relevant information.

You should clearly indicate the table names and any primary or foreign keys that you use.

[8]

DOCTORS(DoctorId, DoctorName, DoctorTelephone)
PATIENTS(PatientId, PatientName, PatientAddress)
APPOINTMENTS(PatientId, DoctorId, Date, Time)
(a combined key field)

Underlined fields are key fields, overlined fields are foreign fields.

(ii)

Doctors sometimes visit patients away from the surgery. The surgery receptionist records which doctor is to visit which patient and the address, date and time of the visit.

Add an extra table to your database design, to accommodate this extra information.

[2]

VISITS(DoctorId, PatientId, Date, Time)
(a combined key field)

The Patient's address is to be found in the PATIENTS table.

[11]

In the following question, additional credit (up to 3 marks) will be given if your answer demonstrates skill in written communication.

A car manufacturer has thousands of dealerships throughout the world. Mechanics in each dealership repair and service the manufacturer's cars. The manufacturer decides to install a new computer system in all the dealerships' workshops.

The system will allow access to:

an expert system to diagnose car faults
the Internet and the manufacturer's intranet

Describe how the mechanics could make use of the expert system, the Internet and the manufacturer's intranet.

Describe any advantages for the mechanics, the customers and the manufacturer of installing such a system.

Describe any drawbacks of installing such a system.

[9+3]

The mechanics could use the expert system to input car faults and output a diagnosis of the fault, together with an advised method of repair.

The expert system is able to store vast amounts of information about different cars - far more than a mechanic can remember. There is also less chance of the computer being mistaken about a diagnosis, which means that customers will get a more reliable service. The accumulated knowledge of an expert system is not diminished by a mechanic leaving or retiring. As new makes and models of cars are developed, information can be added to the expert system.

The mechanics could use the Internet to find out specific information about cars, or order car parts directly from the manufacturers. The manufacturer would be able to advertise on a website and reach prospective customers all over the world.

Customers could use the Internet from their homes to book cars in for repair or service, and the mechanics could use email for booking confirmations.

Mechanics could access the manufacturer's intranet to get news and information about latest developments, new cars, common faults etc.

One of the drawbacks of the expert system may be the initial cost of equipment and installation.