AQA A LEVEL (7517/2) COMPUTER SCIENCE PAPER 2 QUESTION PAPER+ MARK SCHEME

AQA A LEVEL (7517/2) COMPUTER SCIENCE PAPER 2 QUESTION PAPER+ ANSWERS Baud Rate - answersThe maximum possible number of signal changes that can occur in a wire per second. Bit Rate - answersThe number of bits that can be sent down a wire per second. Integer - answersA whole number that can be positive, negative or zero. Examples: -3, 0, 7, 2013588. Natural (Number) - answersA whole number that is either positive or zero. Examples: 0, 1, 2, 100, 67238. Rational (Number) - answersAny number that can be represented as the fraction 'a/b' where 'a' and 'b' are both integers. Examples: -0.2, 4/5, 1, 1/3. Irrational (Number) - answersAny number that cannot be represented as a fraction. Examples: square root of 2, PI. Real (Number) - answersAny number that can either be rational or irrational. Boolean - answersA value that is either true or false. String - answersA series of characters. Array - answersA variable that can store multiple values of the same data type. Example: Storing the high-scores of a game as integers. Record - answersA variable that can store multiple values that can have different data types. Example: Storing data about a book; a string for the title, an integer for the number of pages, etc. Variable - answersA metaphor for it is that is a box that can store a specific type of item (the data type) and has a name assigned to it (the identifier). Its value can be changed during run-time of the program. Constant - answersA metaphor for it is that is a box that can store a specific type of item (the data type) and has a name assigned to it (the identifier). Its value cannot be changed during run-time of the program. Subroutine - answersThis can be broken down into procedures and functions. Procedure - answersA block of code that performs a specific task that does not return a value. Parameters can be passed into it. Function - answersA block of code that performs a specific task that returns a value. Parameters can be passed into it. Selection - answersThis is when an if statement or select case is used to, for example, check the value of a variable. Iteration - answersThis is when, within the program, there is a loop. Definite Iteration - answersThe number of times that the program will loop is already specified. Example: For loop. Indefinite Iteration - answersThe number of times the program will loop is unknown. Example: Do loop. Nested (structures) - answersThis is when either iterative or selective statements are put inside of each other. Meaningful Identifiers - answersSubroutines, variables and objects should have sensible names. Real Division - answersFinds the value (usually as a decimal) of one number divided by another. Integer Division - answersFinds the integer part of one number divided by another. Integer Remainder - answersFinds the remainder of one number divided by another. Truncation - answersChops the decimal part off a number. Floor - answersRounds a number down to the nearest integer. Ceiling - answersRounds a number up to the nearest integer. AND - answersLogical Operation: Returns true only when both values are true. OR - answersLogical Operation: Returns true as long as at least one of the values are true. XOR - answersLogical Operation: Returns true only when exactly one of the two values is true and not both. NOT - answersLogical Operation: Returns true if the value is false and returns false if the value is true. Exception Handling - answersWhen a try catch is used in the program to deal with any errors that may occur. ByVal - answersWhen a variable is passed into a subroutine as a copy so its value will not be changed. ByRef - answersWhen a variable is passed into a subroutine as a reference so its value can be changed. Local (Variable) - answersA variable that is defined, for example, within a subroutine and cannot be viewed or modified from outside of the block of code is was declared in. Global (Variable) - answersA variable that is declared, usually at the start of the program, and can be accessed and modified from anywhere at all in the program. Recursion - answersA subroutine's definition contains a self-call meaning a function or procedure calls itself as a way of performing iteration. Object-Oriented (Programming) - answersA type of programming paradigm when multiple objects are created and handled to run the program. Example: In a game you might have an object for the player and then multiple objects for the enemies. Procedural (Programming) - answersA type of programming paradigm when you break down a project, usually using a decomposition diagram, into individual tasks which can each be performed by a procedure. Functional (Programming) - answersA type of programming paradigm that is mainly used for calculations. No variables are declared, only functions are used with parameters and return statements. (Object) Instantiation - answersWhen an object is first created using the 'new' keyword. (Object) Constructor - answersA procedure that is called once when an object is created, parameters can be passed into this procedure. (Object) Destructor - answersA procedure that is called once when an object is destroyed, parameters cannot be passed into this procedure. Methods - answersThe subroutines that make up an object. Attributes - answersNon-local variables that make up the object. Public - answersThe scope of a variable when it can be accessed from anywhere within the program or by any linked outside program. Friend - answersThe scope of a variable when it can be accessed from anywhere within the program but not from outside. Private - answersThe scope of a variable when it can only be accessed from within the block of code it was defined in. Protected - answersThe scope of a variable when it can only be accessed within the class it was defined in or by any classes that inherit it. Encapsulation - answersThe exposure of methods and attributes of an object while how they work is hidden. The user should only know how to use the object and not how it works. Example: A vector object, the user should know how to use it to find the magnitude of a vector but not how the object actually finds the magnitude of a vector. Inheritance - answersWhen one object inherits attributes and methods of another base object. Example: You might have a base vehicle object with properties such as the number of wheels and a steering wheel and maybe methods such as drive(). You might make a specific type of vehicle that does these things above but a few extra that other vehicles don't, in this case this vehicle would inherit the base vehicle object. Composition - answersWhen one object is made up of other objects by having them as its attributes. If the base object is destroyed, all the objects that make up the base object are also destroyed. Aggregation - answersWhen one object is made up of other objects by having them as its attributes. If the base object is destroyed, the objects that make up the base object aren't always necessarily destroyed. Polymorphism - answersWhen there are different subroutines with the same identifier that will perform different tasks based on their input. Example: The add() function, when two integers are passed in, might add the two numbers together but, if two strings are input, it might concatenate them. Static - answersA data type that will remain the same size. Example: An array of fixed length 5. Dynamic - answersA data type that has a size that can vary. Example: A stack that changes size as you push and pop items to it. Queue - answersAn abstract data structure that is first in first out, the first item put into it will be the first item to be processed. Enqueue - answersThe method of a queue which adds a new item to the end of the queue. Dequeue - answersThe method of a queue which removes an item from the first position of the queue and shifts all the other elements forward by one. Stack - answersAn abstract first in last out data structure. The first item that is added is the last item that will be processed. Push - answersThe method of a stack that adds a new item to the top. Pop - answersThe method of a stack that removes the item that is at the top of the stack. Peek - answersThe method of a queue, stack, list, etc. It is used to look at the item that will be dealt with next without removing it. Graph - answersA mathematical structure that models the relationship between pairs of objects. Nodes,Vertices - answersThe points in a graph where the items are located at. Connections,Edges - answersThe lines on a graph that connect the nodes together. Adjacency Matrix - answersA way of representing which nodes are connected to each other by a structure where 1 represents a connection and 0 represents no connection. This should be used when you do not have many nodes but have lots of connections. Adjacency List - answersA table where on the left there is a list of all the nodes and on the right there is a list of the nodes that the corresponding node is connected to. This should be used when you have a lot of nodes but not many connections. Weighted (Graph) - answersA graph that has values on the connections representing how much it 'costs' to travel. Example: A road map might be this type of graph as there will be distances on the roads. Directed (Graph) - answersA graph that has connections that only allow you to travel in a single direction. Example: A road map might be this type of graph is there is a one way street. Tree - answersAn abstract data structure that is very similar to a graph as it has nodes and edges. It is visualised as having a hierarchical structure with there being a single root node with all the other nodes being parents to it. This type of graph cannot contain any loops or cycles. Example: An OS might use it for its file structure. Binary Tree - answersA tree where each node cannot have anymore than two children. Pre-Order (Tree Traversal) - answersA type of tree traversal where you process the node first, then you check left node then the right node. Use: Copying the tree. In-Order (Tree Traversal) - answersA type of tree traversal where you check the left node, then process the node then the right node. Use: Read the data in order. Post-Order (Tree Traversal) - answersA type of tree traversal where you check the left and right children nodes, then you process the node. Use: Deleting the tree. Hash Table - answersA data structure usually made up of a table or array. The location of a piece of data within this structure is calculated using the data. Example: If you are storing data about students you might use their names to find a location. Thick (client) - answersA computer that has all of its applications installed on its hard-drive. Thin (client) - answersA computer that uses applications stored on the cloud and typically has one piece of software (usually a browser) to access the applications. JSON - answersWhat language is this? { "name":"adam", "age":"17, "subjects":[ "Computer Science", "Further Maths" ] } XML - answersWhat language is this? <note> <to>Someone</to> <from>Adam</from> <heading>Reminder</heading> <body>Don't forget about this weekend</body> </note> CRUD - answersAn acronym that describes what every database should be able to do. REST - answersThe HTTP that performs the CRUD functions. Client - answersA system that accesses a server. Server - answersA computer that is configured to provide a service to the clients. RAID Array - answersAn array of hard-drives that all contain the same data. It can be used for a file server for many users to access. Port - answersAn addressable location on a network that links to a specific application or process. 80 - answersThe port reserved for HTTP. 25 - answersThe port reserved for SMTP. Socket - answersAn IP address followed by a port (IP : PORT). Port Forwarding - answersA way of configuring your router to direct requests with a specific port to the correct application or process. DHCP (Dynamic Host Configuration Protocol) - answersThe protocol that is used by your ISP to assign your router with a new IP if your IP is dynamic. Routable (IP) - answersA type of IP address that can accessed from anywhere on the internet Nonroutable (IP) - answersA type of IP address that is usually located within a sub-net that cannot be accessed from the internet. IPv4 - answersAn IP address that is represented using four octets. IPv6 - answersAn IP address that is represented using hexadecimal. DNS - answersA type of server that takes a request as a domain and returns the corresponding IP that allows you to start to 'wrap' your message using the TCP/IP protocols. Firewall - answersA piece of software that can block specific ports, IP addresses and protocols and can search packets for specific strings of bits. Dynamic (IP) - answersAn IP address that changes when you restart your router. Static (IP) - answersAn IP address that stays the same when you restart your router. MAC Address - answersA code that is assigned to a piece of hardware that does not change and is used to uniquely identify that bit of hardware. Protocol - answersA set of rules used to allow two or more systems to communicate by making sure the data is readable by all of the systems. Fully Qualified Domain Name - answersA URL that contains the WWW server. Top Level (Domain) - answers'.com' is this type of domain Rounding (Error) - answersA type of error when you have to round a value up or down so the value fits into a given number of bits. Absolute (Error) - answersWhen you calculate a value, it is the difference between the calculated result and the expected result. Relative (Error) - answersThe absolute error divided by the intended value multiplied by 100 percent. Overflow - answersWhen a calculation results in a value that is too big to be stored in a given number of bits. Underflow - answersWhen a calculation results in a value that is too small as the number of bits lack the precision. 7 (bits) - answersThe number of bits used by ASCII. 8 (bits) - answersThe number of bits used by extended ASCII. Analogue - answersA signal that can take any range of values. Digital - answersA signal that can only take discrete values. Vector (Image) - answersA type of image that is made up of a set of instructions. Nyquist's Theorem - answersThe sample rate must be at least twice the highest frequency. (The) Operating System - answersIt hides the complexity of the hardware from the user. High level (language) - answersA user friendly language that needs to be compiled to machine code using either a compiler or an interpreter to run. Low level (language) - answersA type of programming language that is written in hexadecimal and requires an assembler to convert it to machine code for the program to run. Machine code - answersA type of programming language consisting of binary that does not need to be compiled to run. Compiler - answersA type of program translator that coverts all of a high level language into machine code. Interpreter - answersA type of program translator that converts a high level language, one line at a time, into machine code. Assembler - answersA type of program translator that converts assembly language into machine code. (The) stored program concept - answersInstructions in the form of machine code are stored in main memory and are fetched and executed one at a time. Fetch-Execute Cycle - answersMAR <- PC PC <- PC + 1 MBR <- MAR[addressed] CIR <- MBR DECODE EXECUTE Synchronous Data Transmission - answersWhere two systems have their clocks synchronised based on pre-determined protocols. Asynchronous Data Transmission - answersWhen two systems are not synchronised by their clocks so when data is sent between them, you include a start bit and an end bit. Hub - answersA piece of hardware that, when it receives packets of data, it sends it to all of the devices connected to it. Router - answersA piece of hardware that, when it receives packets of data, it only sends them to the device that the packets are meant to be sent to. Usually this is found between networks. This piece of hardware can look at the IP and decide where to route the data to in the world. Star - answersA type of network topology that consists of one server with several clients, each connected to the server by a separate bus. Bus - answersA type of network topology that consists of one server with a single wire connecting all of the clients. Internet - answersThe physical hardware that makes up the global network of networks. World Wide Web - answersThe web pages, data and files that are stored and use the internet. Uniform Resource Locator - answersWhat does URL stand for? Packet Switching - answersWhen a file is transferred on the internet, the file is broken down into packets, each packet is made up of a string of bits. Each packet may take a different route on the internet depending on the traffic. Gateway - answersThe device you pass through to access the internet and to convert between different protocols. Telnet - answersThe protocol used for remote accessing a computer, usually for administration purposes. CSMA/CD - answersThe type of collision detection that makes the computers wait a random period of time before continuing to send data after a collision. Big Data - answersExtremely large data sets that are difficult to store, process and analyse. Data - answersRaw values with no context or meaning. Information - answersData that has been given context. Knowledge - answersSomething that you can deduce from the information. Structured Data - answersData in the form of tables and fields meaning it is easy to sort, query. 1000 (Bytes) - answersHow many bytes are there in a Kilobyte? 1024 (Bytes) - answersHow many bytes are there in a Kibibyte? 1000000 (Bits) - answersHow many bits are there in a megabit? Domain - answersThe range of input values of a function. Codomain - answersThe range of output values of a function. 8 (Bits) - answersHow many bits are there in a byte? Vector - answersAn abstract datatype that contains components (usually x, y and z) and is used to represent positions and directions. Dot Product - answersWhat is the vector function called that when applied to the vectors a and b, is equal to 'ax×bx + ay×by). Subset - answersThe name of a set of values that contains all or some of the values from another set. Proper Subset - answersThe name of a set of values that contains some but strictly not all of the values from another set. Union - answersThe set of values that contains all of the values from both sets. Intersection - answersThe set of values that only contains the values that are found in both sets. 65 - answersThe denary ASCII value for a capital 'A'. Lossless (Compression) - answersA type of compression that reduces file sizes while retaining the same quality. Lossy (Compression) - answersA type of compression that reduces file sizes by reducing the quality of the image. Run Length Encoding - answersA type of lossless compression that is used when there are lots of the same item in a row. Example: In a logo image there are usually large blocks of the same colour. Plaintext - answersThe text that has been decrypted. Ciphertext - answersThe text that has been encrypted. Parallel (Data Transmission) - answersA type of data transmission that involves several wires meaning several signals can be sent at once. Serial (Data Transmission) - answersA type of data transmission that involves a single wire meaning only one signal can be sent at once. (Data) Skew - answersThe result of sending signals down parallel wires over long distances. Arithmetic Logic Unit - answersThe component of the processor that performs the logical and arithmetic operations. Register - answersA small memory location found in the processor. Immediate (Addressing) - answersThe type of addressing where the operand of the instruction is the data. Direct (Addressing) - answersThe type of addressing where the operand of the instruction is the location of the data. Latency - answersThe time, usually in milliseconds, it takes for a packet of data to travel from one location to another. Directly Proportional - answersThe type of relationship is there between bit rate and bandwidth. WiFi - answersA local area network that allows devices to connect wirelessly to a hub/router, usually to access the internet. SSID - answersThe name that is assigned to a network which is visible to the clients that want to connect to it. Local Area (Network) - answersA type of network that is only located in a small area. Example: A home network. Wide Area (Network) - answersA type of network that is located across a large geographical area. Example: The internet. Symmetric (Encryption) - answersThe type of encryption that uses a single key to encrypt and decrypt data. Asymmetric (Encryption) - answersThe type of encryption that uses one key to encrypt the data (usually a public key) and a different key to decrypt the data (usually a private key). Subnet Masking - answersThis is used to check if an IP address is located within a subnet or if the request has to be sent to the internet. Third Normal Form - answersEvery attribute is related to the key, the whole key and nothing but the key. Primary Key - answersA unique code given to each attribute. Example: A car's number plate. FIrst-Class Object - answersThis can be an argument of a function and also the result of a function call. Higher-Order (Function) - answersA function that either takes a function as an input, returns a function as an output or both. Head - answersThe first element of a list. Tail - answersAll of the elements of a list except the first. Append - answersA function that adds an item to the end of a list. Prepend - answersA function that adds an item to the start of a list. Parameter - answersA variable or value that is passed into a subroutine. Abstraction - answersHiding data that the user does not need to see. Model - answersA simplified representation of reality used to simplify a problem. Binary - answersThe number system using base 2. Denary - answersThe number system using base 10. Hexadecimal - answersThe number system using base 16. n - answersThe minimum number of bits that are needed to represent 2^n different values. Two's Compliment - answersThe type of binary representation used for representing negative values. Parity (Bit) - answersThe name of the Bit that is added onto the end of a binary word to make the number of one's either odd or even as a way of performing error checking. Check Digit - answersA digit that is added onto the end of a string that is calculated using the first part of the string, this is a way of performing error checking. Metadata - answersThe extra data stored about an image such as the image's colour depth, width and height. AND - answersWhat logical operation is represented by this truth table? Big O (Notation) - answersA type of notation that is used to used to describe how a function behaves as it tends to a specific value, usually either infinity or zero. Example: In computing you can use use this notation to describe the performance of an algorithm, usually by describing the 'worst case' scenario. Pointer - answersA variable that is declared, usually as an integer, to store the location of a memory address. Assignment - answersSetting a variable to a specific value. Exponentiation - answersRaising a number to a power. Merge (Sort) - answersA recursive sorting algorithm that uses a 'divide and conquer' technique. Priority (Queue) - answersA type of queue where some items are to be processed first over others. Magnitude - answersThe length of a vector. Breadth-First - answersThe algorithm typically used for traversing an unweighted graph. Depth-First - answersThe algorithm typically used for traversing a maze. Reverse Polish (Notation) - answersWhat type of notation is this? 7 8 * 4 + Infix (Notation) - answersWhat type of notation is this? 7 * 8 + 4 Linear (Search) - answersWhat search has a time complexity of O(n)? Binary (Search) - answersWhat search has a time complexity of O(Log₂n)? Merge (Sort) - answersWhat sort has a time complexity of O(nLog₂n)? Bubble (Sort) - answersWhat sort has a time complexity of O(n²)? Shortest Path (Algorithm) - answersWhat type of algorithm is Dijkstra's algorithm. Algorithm - answersA sequence of unambiguous instructions to complete a task in a given time. Such That - answersIf you have the following set: A = {x | x ∈ ℕ ∧ x ≥ 1 } What does '|' mean? And - answersIn set theory, what does '∧' represent? Or - answersIn set theory, what does '∨' represent? Infinite (Set) - answersA set that contains a range of continuous values. Finite (Set) - answersA set that contains a range of countable discrete values. Cardinality - answersThe number of elements in a finite set. Union - answersThe set operation that returns a set of all of the values from the two sets. Intersection - answersThe set operation that returns a set of all of the values that are the same from the two sets. a* - answersA regular expression that represents any number, including zero, of the letter 'a'. a+ - answersA regular expression that represents any number, *not* including zero, of the letter 'a'. a? - answersA regular expression that represents either one or zero letter 'a's. a|b - answersA regular expression that represents either the letter 'a' or the letter 'b'. Data Definition Language - answersIn the context of databases, what does DDL stand for? Tractable (Problem) - answersA problem that can be solved in polynomial time. Backus-Naur Form - answersWhat is the name for this type of language? <digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 <integer> ::= <digit> | <digit><integer> Handshaking (Protocol) - answersThe protocol to check a device is connected and is ready to send data and to make sure the devices have agreed on how the data will be transmitted. Server-Side Script - answersA sequence of instructions that is run on a web server when a web page is requested. This is usually used to generate the content of the website. Recursion - answersThe technique that can be used in Backus-Naur Form to perform iteration that cannot be used in regular expressions. Root Node - answersThe node of a tree of which all the other nodes are directed away from Intractable (Problem) - answersA problem that exists and has no efficient solution and cannot be completed in polynomial time. Entity-Relationship (Diagram) - answersIn the context of databases, what is the name of this type of diagram? Structured Query Language - answersWhat does SQL stand for? SELECT - answersThe SQL command used to *extract* data from a database. UPDATE - answersThe SQL command used to *change* data in a database. DELETE - answersThe SQL command used to *remove* data from a database. INSERT - answersThe SQL command used to *add* new data to a database. Normalisation - answersIn the context of floating point binary, what is done to maximise precision using the given number of bits? Inheritance (Diagram) - answersWhat type of class diagram is this? Bluetooth - answersA short range wireless signal used for transferring data, usually to create a personal area network. Universal (Turing Machine) - answersA Turing machine that can simulate the behaviour of any other Turing machine and can complete any other computable sequence. Heuristic - answersThis is what a programmer might use to begin to solve an intractable problem, it makes a guess based on experience. This provides a close to optimal solution. System Development Life Cycle - answersWhat is made up of the following five steps? - Analysis - Design - Implementation - Testing - Evaluation Analogue to Digital Conversion - answersWhat does ADC stand for? Digital to Analogue Conversion - answersWhat does DAC stand for? GET - answersThe server script method that is used to get data from the *URL*. POST - answersThe server script method that is used to get data from a *form*. Random Access Memory - answersWhat does RAM stand for? Bus - answersThe name for a wire. Load Into The Accumulator - answersIn assembly language, what does LDA stand for? (The) (Processor) Instruction Set - answersAll of the different operations that a processor can perform, it is usually different for each processor. Operator - answersThe left half of an instruction that states what will happen to the data. Operand - answersThe right half of an instruction that is the data that will be processed. Vectored (Addressing) - answersA type of indirect addressing where the memory location you access contains a pointer to a different memory location. # - answersIn assembly language, what symbol is used to denote that a number used in the operand is a value instead of a memory location. Network - answersTwo or more computers connected together. (John) Von Neumann (Architecture) - answersThe type of computer architecture where data and instructions are stored in the same memory location. Harvard (Architecture) - answersThe type of computer architecture where data and instructions are stored in separate memory locations, this means separate buses are needed for data and instructions. Bar Code Reader - answersA piece of hardware that is used to read a one dimensional series of black lines, this is usually used in a shop to gather data about the item, for example the price. QR Code Reader - answersA piece of hardware that is used to read a black and white two dimensional code of squares, they are normally used to store URLs. Charged Coupled Device - answersIn a digital camera, what does CCD stand for? Radio Frequency - answersIn the context of RFID tags, what does the 'RF' stand for? Basic Input Output System - answersWhen a computer is started up, the BIOS in run. What does BIOS stand for? Driver - answersA piece of software that translates the signals from the hardware into calculations that the processor can perform. Magnetic Hard Drive - answersA type of secondary storage that uses a change in polarisation of a magnet to represent a 1 and no change to represent a 0. Solid State Drive - answersA type of secondary storage that used logic circuits to store the data, it has no moving parts. Read Only Memory - answersA type of primary storage that cannot be edited. An example of this being used is to store the instruction set specific to that processor. Volatile (Memory) - answersA type of memory that is lost when it loses power. Non-Volatile (Memory) - answersA type of memory that is *not* lost when it loses power. Virtual Memory - answersThis is used when a program is to big to be entirely stored in ram and a section of the hard drive must be used. Software - answersThe programs or instructions that run on a computer to perform a specific task. Generic - answersThe type of software that can have many different uses. Specialist - answersThe type of software that only works for mainly one purpose. Bespoke - answersThe type of software that is specifically designed for one client and is generally expensive, takes a while to develop and difficult to maintain. System (Software) - answersA type of software that is used to run the computer, the user does not interact with it. Sound Card - answersThe piece of hardware that converts analogue sound signals into digital signals. Sampling Resolution - answersThe number of bits per sample. Switch - answersIt is similar to a hub but it doesn't send the data to every client, it redirects the packets to the correct client. Usually they are found between network segments. FTP - answersThe protocol that is used to transfer files. It is used over HTTPS as if your connections is lost during a file transfer then your transfer progress is saved allowing you to continue. 1600 (Hz) - answersIf you are converting sound that has a highest frequency of 800Hz, what is the minimum sample rate you should choose? Accessor (Method) - answersA type of method used in a class that is used to return an attribute that is private.