Computer Science Questions and Answers.

1 (a) Using diagrams, or otherwise, describe the following network topologies.

(i) Bus network [1]

(ii) Ring network [1]

(iii) Star network [1]

(b) State an advantage of each of the networks in (a). [3]

Answer

2 Describe how an EPOS (electronic point of sale) system operates in a large store with many EPOS terminals. Your answer should include reference to

· the input of any necessary data,

· the output to the customer,

· The stock control and ordering. [8]

Answer:

3 An algorithm has been produced which inputs two numerical values and outputs the larger one.

Select three pairs of numbers that could be used as test data. Explain what each pair of numbers is intended to test. [6]

Answer:

4 (a) Describe one difference between read-only memory (ROM) and random access memory (RAM) in the memory of a computer. [2]

(b) State one use for each of ROM and RAM in the primary memory of a computer. Make clear why the type of memory is appropriate for that use. [4]

5 An information system is to be installed in a bus station. There will be a number of terminals for use by passengers who will be able to make enquiries about times of buses and the stops that they will make on the journey. The terminals will be in the open air. The terminals will be networked with a server in the main office.

(a) State a peripheral hardware configuration for this system, giving reasons for your answers. [8]

(b) It is decided to use a menu-based software interface.

(i) Explain what is meant by a menu-based software interface. [2]

(ii) State two reasons why this is a sensible choice of interface. [2]

Answer:

6 A file of different types of musical instruments sold in a music shop is to be stored on a computer system. The file is to be stored as a linked list in alphabetical order of the name of the instrument.

(a) Using a diagram, show how such a list would store the instruments lute, fiddle, guitar, and zither. [4]

(b) Describe an algorithm to find the details of a lute. [4]

Answer:

7 State four factors that should be considered as part of a feasibility study, explaining the importance of each. [8]

Answer:

8 Communications across a network can be done by using circuit switching or packet switching.

(a) Explain the difference between circuit switching and packet switching. [2]

(b) Give one advantage of using

(i) circuit switching

(ii) packet switching

when sending data across a network. [2]

The remaining questions refer to the following information.

A telephone company stores details of its customer accounts on a computer file. The file is used to allow the company to calculate and send out bills to its customers at regular times of the year. The file is also used to allow an immediate response to a customer who calls in to make an enquiry about their account.

9 Explain why indexed sequential access to the data would be sensible in this example. [4]

10 Customer records are stored using an 8 digit customer number as key.

Describe an indexing system which could be used to produce such indexed sequential access to the file. [3]

11 Backups and archives are taken from the customer file.

By describing systems that could be implemented by the company for taking backup files and archive files, explain the differences between them. [4]

12 When a customer makes a payment, the file is amended by entering the account number and the amount that has been paid in.

(a) Describe two validation tests that can be carried out on the amount of money paid in. [4]

(b) State what is meant by a check digit, and explain how it could be used to validate the account number. [4]

13 The operators who enter the data into the files sit at keyboards to do their work.

Discuss

(i) the potential health hazards of this type of work,[7]

(ii) the ways that management can help to overcome the effects of the health hazards.

14 A Management Information System (MIS) is used by the company. With reference to possible reports produced from the data in the customer accounts file, distinguish between the two types of report which the MIS will produce. [6]

Answer:

1. (a) Distinguish between operating system software and applications software. [2]

(b) State three utility programs associated with the use of a hard drive. Explain the purpose of each of the programs. [6]

Answer:

1 (a) - OS controls operation of system/hardware

- Applications software allows the system to do something useful (2)

(b) - File handling

- Copy/move/delete

- Anti virus software

- To protect files from attack by virus

- Defragmentation

- To keep files sensibly arranged on the hard drive

- Format

- To divide surface of drive into smaller areas to aid storage

(1 per -, max 6) (6)

2 (a) State what is meant by each of the following modes of use.

(i) Batch processing.

(ii) Real-time processing.

(iii) On-line processing.

(iv) Off-line processing. [4]

(b) A computer game involves driving a racing car around a track. State which two of the above modes of use would be appropriate, justifying your answers. [4]

(c) State two advantages and one disadvantage of having a network of computers, rather than a series of stand alone machines, in a school classroom. [3]

Answer:

2 (a) (i) Jobs collected together for processing at a later time

(ii) Output produced quickly enough to affect the next input

(iii) User has direct contact with processor

(iv) User cannot communicate directly with processor (4)

(b) - Real time

- E.g. turning the wheel must turn the car immediately

- On line

- Otherwise system cannot be real time (4)

(c) - Sharing of software and data files

- Sharing of hardware, e.g. printers

- Communication

- Security of files more of a problem

(1 per -, max 3) (3)

3 (a) Describe each of the following types of program error, giving an example in each case.

(i) Syntax error.

(ii) Logic error.

(iii) Arithmetic error. [6]

(b) Describe two methods used to assist in finding program errors. [4]

Answer:

3 (a) (i) Incorrect use of language, e.g. PLINT instead of PRINT

(ii) A mistake in the structure of the solution, e.g. a jump goes to the wrong line

(iii) Inappropriate arithmetic is used, e.g. division by 0 is attempted (6)

(b) - Translator diagnostics

- Produced when wrong programming used

- Gives position and explanation of error

- Cross-referencing

- Used when program modularized

- To check use of variables

- Trace routines

- Follow value of variable

- To give clue as to where error occurs

- Variable dump

- Prints values of all variables

- At given point in program

(1 per -, max 2 per type, max 4) (4)

4 (a) Explain what is meant by a LIFO data structure. [2]

(b) Draw a simple diagram to show how a stack can be stored in an array. [2]

Answer:

4 (a) - Data enters at one end (of a stack)

- Leaves at the same end

- Hence 'last in, first out'

(1 per -, max 2) (2)

(b)

5 A company employs approximately 2000 workers whose details are stored in a personnel file in a computer system.

Each worker's record has a unique 7 digit identification number.

_ The first digit is from 0 to 5 and refers to the department in which the person works.

_ The second digit is a 0 or a 1 and refers to the sex of the employee.

_ The next two digits refer to the year that the employee joined the company.

_ The last three digits are used to make the identification number unique.

The file is accessed randomly by using a hash table.

(a) Devise a suitable hashing algorithm which limits the degree of redundancy to allow access to the hash table. [2]

(b) State two identification numbers that will cause a collision using your hashing algorithm. [1]

(c) Describe two methods to overcome the problem of collision in part (b). [4]

Answer:

5 (a) - Uses all 7 digits

- Creates >2000 results

- Highlight the danger of multiplying by zero (2)

(b) Any two 7 digit numbers that cause a clash (1)

(c) - Search serially from hash value

- Until vacant location found

- Mention of circular reference

- If the memory locations become full, use a bucket

- Use bucket to place duplicates in

- In serial form

- Pointer to bucket from hashed location

- Use hashed location as start of linked list

- Ensure end of list with null value of pointer

(1 per -, max 2 methods, max 4) (4)

6 (a) Describe the purpose of the

(i) control unit

(ii) memory unit

(iii) arithmetic logic unit in a computer. [6]

(b) Explain the difference between main memory and secondary storage. [2]

Answer:

6 (a) (i) To manage the execution of instructions

By running a clock

To decode instructions

(ii) To store OS

To store those parts of applications programs currently running

To store data currently in use

(iii) Part of processor where data is processed/manipulated All I/O must pass through here

(1 per -, max 2, 2, 2, max 6) (6)

(b) - Main memory transitory, secondary storage is (semi-)permanent

- Processor can only use data/instructions that are in main memory

- Main memory in processor, secondary storage not

(1 per - max 2) (2)

7 (a) Explain the difference between

(i) serial and parallel,

(ii) simplex and duplex modes of data transmission. [4]

(b) When data is transmitted it is subject to corruption. Explain how a parity check could be used to determine whether corruption has taken place. [4]

4 The remaining questions refer to the following information.

A college stores its student files on paper, which is kept in filing cabinets. The decision is taken to computerize these student files.

A systems analyst is employed to supervise the process.

Answer:

7 (a) - Serial is the transmission of data one bit at a time/through one wire

- Parallel is the transmission of data more than one bit at a time/many wires

- Simplex is the transmission of data in one direction only

- Duplex is the transmission of data in both directions simultaneously (4)

(b) - Extra bit on each data-byte that

- Does not transmit data

- Makes number of ones in a byte be always even or always odd

- Error in the transmission of a bit will make the even/odd wrong

- Problem of two errors in one byte not being found

- Parity block

(1 per -, max 4)