set 3 (random)

Question 1

Describe what happens, in relation to the storage or retrieval of a record in the file when the calculated hash value is a duplicate of a previously calculated hash value for a different record key

Answer 1

• If a collision occurs when the record key doesn’t match the stored record key this means that the determined storage location has already been used for another record.
• If the record is to be stored, it searches the file linearly to the next available storage space (closed hash) or searches the overflow area linearly to find the next available storage space (open hash)
• If the record is to be found, it searches the overflow area linearly (open hash) until the matching record key is found or searches linearly from where you are (closed hash) until the matching record key is found.
• If not found record is not in file

Question 2

State, with a reason, where it would be appropriate to use circuit switching

Answer 2

• Circuit switching is used where a dedicated path needs to be sustained throughout the call where the whole bandwidth is required // when real time communication is used
• A typical application is standard voice communication, video streaming or private data networks

Question 3

What are the benefit of circuit switching

Answer 3

• Whole bandwidth available
• Data transmitted with a fixed data rate
• no waiting time at switches
• suitable for long continuous communication
• data arrives in same order as it was send, so easier method of data transfer

Question 4

What are the drawbacks of circuit switching

Answer 4

• A dedicated connection makes it impossible to transmit other data even if the channel is free
• Not very flexible
• The time required to establish the physical link between the two stations can be too long
• No alternative route in case of failure

Question 5

Outline the characteristics of massively parallel computers.

Answer 5

• A large number of computer processors / separate computers connected together
• simultaneously performing a set of coordinated computations // collaborative processing
• Communicate using a message interface / by sending messages.

Question 6

Explain how a new element can be added to the queue if it is implemented using two stacks.

Answer 6

• (Two stacks are required) so that the second stack can reverse the order of the first stack.
• Stack 1 operates as the queue with the newest elements at the bottom. Stack 2 is empty.
• To add an element, pop all the elements from stack 1 and push onto stack 2.
• Push the new element onto either stack. Pop all the elements of stack 2 back onto stack 1.

Question 7

Describe what is meant by recursion.

Answer 7

• A process using a function or procedure defined in terms of itself / calls itself.
• A recursive process must have a base case (which is a way to return without making a recursive call) // terminating solution // concept of unwinding described
• There must (also) be a general case where the recursive call takes place.

Question 8

Define encapsulation

Answer 8

putting properties and methods inside a class // ensures sensitive data is hidden from users by hiding values of a structured data object inside a class.

Question 9

Define OOP

Answer 9

a programming
methodology that uses self-contained objects, which
contain programming statements (methods) and data, and which communicate with each other.

Question 10

Define Polymorphism

Answer 10

allows the same method to take on different behaviours depending on which class is instantiated // methods can be redefined for derived classes.

Question 11

Describe the purpose of quantum cryptography

Answer 11

• To produce a virtually unbreakable encryption system using the laws of quantum mechanics
• It can detect eavesdropping because the properties of photons change to protect security of data transmitted over fibre optic cables
• To enable the use of longer keys

Question 12

What is meant by the term Enumerated data type

Answer 12

A user defined non composite data type with an ordered list of possible values

Question 13

What is meant by the term pointer data type

Answer 13

A user defined non composite data type used to reference a memory location

Question 14

Define what an Instance is

Answer 14

an occurrence of an object // a specific object based on the class // an instantiation of a class

Question 15

Define inheritance

Answer 15

the capability of defining a new class of objects that has all the attributes and methods from a parent class.

Question 16

Define getter and setter

Answer 16

Getter – method that is used to return the value of a property.

Setter – method that is used to update the value of a property.

Question 17

Explain the need for scheduling in process management.

Answer 17

• Process scheduling allows more than one program/task to appear to be executed at the same time / enables multitasking / multiprogramming.
• To allow high priority jobs to be completed first.

To keep the CPU busy all the time to ensure that all processes execute efficiently and to have reduced wait times for all processes / to ensure all processes have fair access to the CPU / prevent starvation of some processes.

Question 18

Describe shortest job first and a benefit for it

Answer 18

Process are executed in ascending order of the amount of CPU time required // Short processes are executed first and followed by longer processes.

• Leads to an increased throughput (because more processes can be executed in a smaller amount of time).

Question 19

Describe round robin and a benefit for it

Answer 19

Each process is served by the CPU for a fixed time/time slice (so all processes are given the same priority).

Starvation doesn’t occur (because for each round robin cycle, every process is given a fixed time/time slice to execute).

Question 20

Describe round robin and a benefit for it

Answer 20

No complex logic, each process request is queued as it is received and executed one by one.

Starvation doesn’t occur (because every process will eventually get a chance to run) // less processor overhead.

Question 21

State the purpose of a flip flop

Answer 21

To store a binary digit / a single bit

Question 22

Describe what is meant by a virtual machine.

Answer 22

• The emulation of a computer system - hardware and software
• Using a host computer system
• Using guest operating system for emulation

Question 23

What are benefits of a VM

Answer 23

• Multiple guest operating systems / VMs can be used on the same computer.
• Different instruction set architectures can be emulated on a single computer.
• A virtual machine can crash without affecting the host machine.
• There are security benefits // Trying a piece of suspicious software and if it is / has a virus, it will only infect the virtual machine.
• Cost savings due to not needing to purchase extra hardware.
• Can run legacy applications that are currently incompatible.

Question 24

what are the drawbacks of a VM

Answer 24

• A virtual machine is less efficient / has poorer performance than real machines because of extra load on the host computer
• Performance of the guest system cannot be adequately measured.
• A virtual machine may be affected by any weaknesses of the host machine.
• Costly and/or complex to maintain / implement / manage.
• Cannot emulate some hardware.

Question 25

Define properties

Answer 25

• The data items / attributes
• The data types // characteristics
• defined in a class

Question 26

Define Methods

Answer 26

The procedures/ functions in a class implementing the behaviours that act on the properties / attributes Inheritance

Question 27

State the reasons for including exception handling routines when writing a program.

Answer 27

• To trap (some) runtime errors To prevent a program halting unexpectedly
• To produce meaningful error messages for these errors
• Example divide by zero // end of file // file not found

Question 28

Compare sequential and serial methods of file organisation.

Answer 28

• In both serial and sequential file records are stored one after the other and need to be accessed one after the other
• Serial file are stored in chronological order
• Sequential files are stored with ordered records and stored in the order of the key field
• In serial file, new record are added in the next available space
• In sequential files, new records are inserted in the correct position