A Level Computer Science 9618 Paper 32, May/June 2024

When the number of bits in the mantissa is raised, the precision / accuracy of the number represented increases // when the number of bits in the mantissa is lowered, the precision / accuracy of the number represented reduces.

When the number of bits in the exponent is reduced, the range of numbers that can be represented is reduced // when the number of bits in the exponent is increased, the range of possible numbers that can be represented increases.

When the range increases the accuracy decreases // When the range decreases the accuracy increases.

number converted to binary e.g. 54.8125 = 00110110.1101 // Fractions method 1/2 + 1/4 + 1/16 + 1/32 + 1/128 + 1/256 + 1/1024 = 877/1024 // 32 + 16 + 4 + 2 + 0.5 + 0.25 + 0.0625 / (1/2 + 1/4 + 1/16)

exponent = 6 // Moving binary point the correct number of places

correct answer: Mantissa 0 1 1 0 1 1 0 1 1 0 1 0, Exponent 0 1 1 0

Protocols provide a standard set of rules that enables successful data transfer between devices.

Allows communication between devices on different platforms.

Makes communications independent of software and hardware.

Sending - SMTP

Receiving – POP3 // IMAP // Post Office Protocol 3

BitTorrent allows the sharing of files between thousands of users who are connected together over the internet.

It allows more users to share files with each other than would be the case with a peer-to-peer network.

Users share files directly with each other // the users' computers are acting as peers

… no web server / central device is used // all users are of equal status.

A data type that is defined without referencing another data type.

It can be a primitive data type found in a programming language or a user-defined data type.

Example – enumerated data type / pointer data type / allow a correct example of an enumerated or pointer data type declaration.

Type statement fully correct

DEFINE EvenNumbers

Correct list of values in brackets

: <set identifier> from Type statement used

Sheila's computer uses an algorithm to generate a matching pair of keys private and public

Sheila's computer sends Fred's computer Sheila's public key // Fred's computer acquires Sheila's public key

Fred's computer encrypts the document/plain text using Sheila's public key to create cipher text

Fred's computer sends the cipher text to Sheila's computer The cipher text can only be decrypted using Sheila's private key // Sheila's computer uses Sheila's private key to decrypt the cipher text.

7 2 – 8 +

9 5 - /

First ring (stacks 1, 2, 3: [6], [9, 6], [15])

Second ring (stack 4: [6, 15])

Third ring (stacks 5, 6, 7, 8: [3, 6, 15], [9, 15], [7, 9, 15], [2, 15])

Fourth ring (stack 9: [30])

(a – c + b)

* (d + b)

/c

working, all five columns P, Q, R, S and T

first four rows of column Z

second four rows of column Z

Two marks for all six correct terms only (Z = Ā.B̄.C + Ā.B.C̄ + Ā.B.C + A.B̄.C + A.B.C̄ + A.B.C) // One mark for any three correct terms

Two marks if all correct / One mark if only one error present

Correct loop for group of 4 (columns 11 and 10)

Correct loop for group of 4 (wraparound columns 00 and 10)

B + C̄

Direct access allows a record to be found in a file without other records being read.

Records are found by using the key field of the target record // the location of the record is found using a hashing algorithm.

In sequential files, an index of all key fields is kept

The index is searched for the address of the file location where the target record is stored.

A hashing algorithm is used on the key field of the record

… to calculate the address of the memory location where the target record is expected to be stored.

Method to find a record if it is not at the expected location e.g. linear probing, search overflow area etc.

WHILE Found = FALSE AND NotInList = FALSE // Count <= EndOfList

IF ToFind = Widgets[Count] // Widgets[Count] = ToFind THEN

Count ← Count + 1

IF Found = FALSE AND Count > EndOfList THEN

Linear search sequentially checks each element of the array / list.

… until the matching element is found, or the end of the array / list is reached.

Binary search finds the mid-point of an array/list and determines which side contains the item to be found

… it discards the half of the array/list not containing the search item // … it finds the position of a target value within an array / list by repeatedly halving the target search field.

The binary search requires the elements to be sorted // The linear search does not require the elements to be sorted.

The binary search will usually do many fewer comparisons of records/iterations against the target than a linear search before it finds its target.

Linear search starts at the beginning of the array/list and binary search starts in the middle of the array/list.

Big O for binary search is O (Log₂ n)

Big O for linear search is O (n)

Big O notation is used to indicate the time / space complexity of an algorithm

COMPATIBILTY e.g. Applications that aren’t compatible with the host computer can be run on the virtual machine // It is possible to emulate old software on a new system by running a compatible guest operating system as a virtual machine // Software can be tried on different OS on the same hardware.

PROTECTION e.g. The guest operating system has no effect on anything outside the virtual machine other virtual machines or the host computer//Virtual machines are useful for testing as they will not crash the host computer if something goes wrong // Easier to recover if software causes a system crash as virtual machine software protects the host system.

COST e.g. No need to buy extra computers / hardware as multiple virtual machines can be implemented on the same hardware.

PERFORMANCE e.g. The performance of the guest operating system will not be as good on a virtual machine as it would be on its own compatible machine because of the extra code / using more RAM/memory space // The performance of the VM is dependent on the capabilities of the host computer // Response times cannot be accurately measured using a virtual machine.

COMPLEXITY e.g. Building an in-house virtual machine can be expensive, time consuming and complex to maintain / set-up.

HARDWARE/SOFTWARE ISSUES e.g. Some hardware/software can’t be emulated with a virtual machine // Some of the host machine’s hardware can’t be directly accessed by the virtual machine.

The host operating system is the normal operating system for the host computer / machine.

It has control of all the resources of the host computer / machine. // It can access the physical resources of the host computer / machine.

It provides a user interface to operate the virtual machine software.

It also runs the virtual machine software.

The guest operating system runs within the virtual machine.

… it controls the virtual hardware/software during the emulation. // It accesses the actual hardware through the virtual machine and host operating system.

It provides a virtual user interface for the emulated hardware/software.

The guest operating system runs under the control of the host operating system.

(25) client(jane).

(26) activity(surfing).

(27) choice(jane, surfing).

(28) done(jane, sailing).

(List =) frankie, erik, henry

client(C)

activity(A)

done(C, A)

all correct Boolean operators and punctuation (allow , for AND). There must be the correct number of terms and no additional lines of code

Reinforcement learning is a machine learning technique based on feedback / rewards / punishment.

… in which an agent learns to behave in an environment by performing the actions and seeing the results of the actions.

… for each good action, the agent gets positive feedback / reward and each bad action receives negative feedback / punishment.

The agent learns automatically using feedback without any labelled data / specific instructions.

Adjust node weightings to achieve the correct outcome. // Using feedback to improve its performance at accomplishing similar tasks.