computer science 13,14,15,16,17,18

Question 1

describe the purpose of a user defined data type 2

Answer 1

1. to create a new data type from existing data types
2. to extend the flexibility of the programming language

Question 2

explain how an interpreter executes a program without producing a complete translated version of it 4

Answer 2

1. an interpreter examines the source code 1 line at a time
2. and checks each statement for errors
3. if no error is found, the statement is executed
4. if an error is found, it’s reported and the interpreter haults

Question 3

explain why the reverse polish notation (RPN) is used to carry out the evaluation of expressions 2

Answer 3

1. RPN provides an unambiguous method of representing an expression
2. reading from left to write

Question 4

identify with reasons, a data structure that could be used to evaluate an expression in RPN 2

Answer 4

structure: stack
- the operands are popped from the stack in the reverse order to how they were pushed

Question 5

give 2 benefits and 2 drawbacks of packet switching 4

Answer 5

benefit 1: accuracy - it ensures accurate delivery of the message

benefit 2: completeness: missing packets can be easily detected and a re-send request is sent so the message arrives complete

drawback 1: network problems may introduce errors in the packets

drawback 2: it requires complex protocols for delivery

Question 6

explain he reason why binary numbers are stored in normalised form 3

Answer 6

1. to store the maximum range of numbers in the minimum number of bits
2. it enables very large numbers to be stored with accuracy
3. it avoids the possibility of many numbers having multiple representations

Question 7

compare sequential and serial methods of file organisation 4

Answer 7

1. in both , records are stored one after the other and need to be accessed one after the other
2. serial files are stored in chronological order

3.sequential files are stored with ordered records

4. in serial, new records are added in the next available space
5. in sequential, new records are inserted in the correct position

Question 8

state the most suitable method of file access when a record is referenced by a unique address on a disk-type storage medium 1

Answer 8

direct acess

Question 9

state the most suitable method of file access when a bank stores its data records in ascending order of account number 1

Answer 9

sequential access

Question 10

explain how packet switching is used to transfer messages across the internet 5

Answer 10

1. a large message is divided up into a group of smaller chunks of the same size called ‘packets’
2. the packet has a header and payload
3. the header contains a source IP address, destination IP address and sequence number
4. each packet is dispatched independantly
5. the packets may arrive out of order

Question 11

outline the function of a router in packet switching 3

Answer 11

1. the router examines the packet’s header
2. a router has access to a routing table
3. containing information about e-gateways

Question 12

a record is a user-defined composite data type

explain what is meant by a user-defined composite data type and include an example of another user-defined composite data type 3

Answer 12

a composite data type refers to other/many types, user-defined data types created by the programmers to suit specific needs. an example, in python, you can create user-defined data types using classes

Question 13

describe what is meant by RISC and CISC processors ( 2 points for each)

Answer 13

RISC- it uses simple instructions and fixed length instructions

CISC- it uses many instruction formats and uses variable length instructions

Question 14

identify 2 differences between RISC and CISC processors 2

Answer 14

RISC has fewer instructions while CISC has more instructions

RISC has many registers while CISC has fewer registers

Question 15

outline the functions of the Transport and Internet layers of the TCP/IP protocol suite 5

Answer 15

Transport layer:
- it regulates the network connections
- data is broken up into packets which are then sent to the internet layer

internet layer:
- it identifies the intended network and host
-it moves traffic across local segments
-encapsulates IP packets into frames for transmission

Question 16

state what is meant by enumerated data type

Answer 16

a non-composite user-defined data type defined by a given list of all possible values

Question 17

what is meant by the term pointer data type

Answer 17

a non composite data type that uses memory address of where the data is stored

Question 18

describe the process of pipelining during the fetch execute cycle in RISC processors 4

Answer 18

• instructions are subdivided into tasks
  -each subtask is completed during one clock cycle
  -No 2 instructions can be executed during the same stage at the same clock cycle
  -the second instruction begins in the second clock cycle while the first instruction has moved on to it’s second subtask

Question 19

explain why a protocol is used in communication between computers 2

Answer 19

• both parties need to agree the protocol being used to ensure successful communication, eg. parity checking, without agreeing this protocol, it would be impossible to do a parity checking

Question 20

describe the purpose of IMAP protocol

Answer 20

it’s a pull protocol used when receiving emails from an email server

Question 21

describe how records are organised and accessed in a sequential file 3

Answer 21

1. records are stored one after the other and are accessed one after the other
2. the files are stored in particular order.
   3.new records are added based on the key field

Question 22

state 2 examples where it would be appropriate to use packet switching 2

Answer 22

1. commonly used on data networks such as the internet to send large data files that don’t need to be to be live streamed
2. used for emails text messages, documents

Question 23

describe the use of pipelining in RISC 2

Answer 23

1. pipelining allows several instructions to be processed simultaneously
   2.each instruction is completed during one clock cycle

Question 24

explain the use of graphs to aid AI 3

Answer 24

• graphs provide structures for relationships
• graphs may be analysed
• Artificial Neural Networks can be represented using graphs

Question 25

describe the purpose of SSL and TLS PROTOCOLS 2

Answer 25

- they provide encryption - they enable two parties to identify and authenticate each other

Question 26

explain how SSL/TLS protocols are used when a client-server communication is initiated 4

Answer 26

an SSL/TLS connection is initiated by an application which becomes the client every new session begins with a handshake and the encryption algorithms are agreed

Question 27

state the reason for having multiple hidden layers in an artificial neural network

Answer 27

it enables deep learning to take place

Question 28

explain how artificial neural networks enable machine learning 4

Answer 28

1- artificial neural networks are intended to replicate the way human brains work 2- the data are input at the input layer and are passed into the system 3- decisions can be made without being specifically programmed 4-the output layer provides the results

Question 29

state 2 uses of stack

Answer 29

procedure calls interrupt handling

Question 30

describe 2 benefits and 1 limitation of using a virtual machine for this purpose 6

Answer 30

benefit 1 : new system can be tried on different virtual hardware without need to purchase the hardware benefit 2 : easier to recover if software emulating the new computer causes system crash as VM provides protection to other software limitation : a virtual machine may not be as efficient so processing time is increased

Question 31

what is meant by deep learning

Answer 31

it uses Artificial neural networks that contain a high number of hidden layers

Question 32

what is meant by virtual memory

Answer 32

secondary storage that is used to extend the RAM virtual memory is created temporarily

Question 33

state one difference between paging and segmentation in the way memory is divided

Answer 33

paging allows the memory to be divided into fixed blocks and segmentation divides the memory into variable sized blocks

Question 34

outline the reasons for deep learning 2

Answer 34

-deep learning makes good use of unstructured data -it provides a more accurate outcome with higher number of hidden layers

Question 35

state when an underflow occurs in binary floating-point system

Answer 35

when following a logical operation and the results are too small to be represented in the available system

Question 36

outline the purpose of syntax analysis

Answer 36

it checks that the code matches the grammar of the language syntax errors are reported

Question 37

describe what is meant by a virtual machine state 2 benefits and 2 drawbacks

Answer 37

virtual machine: the emulation of a computer system using a host computer system benefit 1: multiple guest operating systems can be used on the same computer benefit2: cost savings due to not needing to purchase extra hardware drawback1: virtual machines are not efficient drawback2: complex to maintain

Question 38

state 2 differences between symmetric and asymmetric encryption 2

Answer 38

-symmetric uses a single key while asymmetric uses a pair of keys -symmetric single key is used by all, only 1 of the keys for asymmetric is available to everyone

Question 39

explain the process by which an organisation may aquire its digital certificate 4

Answer 39

-the organisation requests a certificate from the CA -the organisation may send their public key -the CA verifies the organisations identity -the CA generates a digital certificate including the organisation's public key and other info

Question 40

describe supervised learning and unsupervised learning in machine learning 4

Answer 40

supervised learning: allows data to be collected and uses labelled input data unsupervised learning: only requires input data to be given and uses any data

Question 41

explain the need for scheduling in process management 3

Answer 41

- to allow the high priority jobs to be completed first -to keep the cpu busy all the time -to ensure that all the processes execute efficiently

Question 42

describe these scheduling routines and identify a benefit for each one shortest job first, round robin, first come first served 6

Answer 42

shortest job first: short processes are executed first and followed by longer processes which leads to an increased throughput because many processes are executed in less time round robin: each process is served by the cpu for a fixed time so starvation doesn't occur first come first served: each process requested is queued as it is recieved and executed one by one and starvation doesn't occur