OCR Computer Science A level paper 1

OCR Computer Science A level paper 1 PC - Correct answer Program counter, contains the address of the next instruction" "CIR - Correct answer Current Instruction Register: stores the address of the next instruction currently being executed and decoded" "Accumulator - Correct answer A storage register in the ALU that holds data temporarily while the data is processed and before it is transferred to memory." "RISC - Correct answer Reduced Instruction Set Computer: Only simple instructions taking one clock cycle are executed - currently more widely used than CISC Advantages: allows for pipelining, execution will be quicker or as fast as CISC Disadvantages: Compiler has to do more work, more RAM required" "CISC - Correct answer Complex Instruction Set Computer: Large instruction set is used to minimise lines of code required - mainly used for microcontrollers and embedded systems Advantages: compiler has very little work to do, not much RAM required Disadvantages: Building in specialised instructions can be inefficient when only ~20% get used per program" "What are the types of memory management? - Correct answer Paging: Available memory is divided into fixed size pages, process in memory can be held in non-contiguous pages, mapped to logical addresses by a page table Segmentation: Divides address space logically into segments of varying length" "What is virtual memory? - Correct answer A technique that uses a portion of the computer's hard disk as an extension of RAM - swaps files in and out of RAM by a process called disk thrashing" "GPU - Correct answer Graphics Processing Unit - dedicated graphics processor on a graphics card, used to render images stored in the RAM of the graphics card." "Multi-core CPU - Correct answer A CPU with more than one core on the same chip - makes use of parallel processing for optimum efficiency" "MAR - Correct answer Memory Address Register, holds relevant memory address (to read from or write to)" "MDR - Correct answer Memory Data Register, stores data being transferred to and from memory, acts as a buffer" "ALU - Correct answer Arithmetic and Logic Unit, does all mathematical calculations and makes all logical decisions" "What affects processor performance? - Correct answer - The number of processor cores: more cores - better performance - The processor's clock speed: faster clock speed - better performance - Amount/type of cache memory: more/better cache memory - better performance" "RAM - Correct answer Random Access Memory - stores programs and data currently in use. Volatile" "ROM - Correct answer Read Only Memory - holds information which must be permanently in memory eg. BIOS" "What are the functions of an operating system? - Correct answer - Providing a user interface - Memory management - Interrupt service routines - Processor scheduling - Backing store management - Input and output management" "What is a distributed operating system? - Correct answer Form of parallel processing system which splits tasks over multiple computers - OS coordinates so that the system appears to the user as a single system" "What is a multitasking operating system? - Correct answer An OS which allows each user to run more than one job at a time." "What is a multi-user operating system? - Correct answer Allows multiple users to use a computer system by allocating each one a slice of processor time - uses a scheduling algorithm" "Closed Source Software - Correct answer Also know as proprietary software, computer software licensed under exclusive legal right of the copyright holder with the intent that the licensee is given the right to use the software only under certain conditions, and restricted from other uses, such as modification, sharing, studying, redistribution, or reverse engineering." "Utility program - Correct answer A small program that performs many of the general housekeeping tasks for the computer, such as system maintenance and file compression - Disk defragmentation, automatic backup/updating, virus checking, compression software" "Scheduling Algorithms - Correct answer - Round robin - Shortest remaining time - Shortest job first - First come, first served - Multi-level feedback queues" "Shortest remaining time - Correct answer A scheduling algorithm that deals with each user or task based on a calculating an estimated time remaining to complete." "Shortest job first - Correct answer A scheduling algorithm that deals with each user or task based on the getting the smaller ones out of the way." "Multi-level feedback queues - Correct answer This algorithm is designed to give preference to short jobs, give preference to input/output bound processes and separate processes into categories based on their need for the processor." "Round Robin - Correct answer Processes are dispatched on a first in first out (FIFO) basis, with each process in turn being given a limited amount of CPU time, called a time slice." "First come first served - Correct answer Processes are carried out by the CPU in the order in which they arrive" "BIOS - Correct answer Basic input/output system contains programs to load the hardware, stored in ROM" "Device drivers - Correct answer Utility software used by the operating system to communicate with peripheral devices." "Virtual machines - Correct answer A software implementation of a computer system, allowing one physical computer to run several "virtual computers", each with their own independent operating system and application software." "Low-level language - Correct answer A programming language that is designed to be easy for a computer to execute; also called machine language or assembly language." "What does a mobile operating system comprise of? - Correct answer Mobile OSes are made up of two separate operating systems: A main system operating the user interface/application software A low-level real-time operating system which is hardware-specific" "What is an embedded operating system? - Correct answer An OS on a chip instead of on a hard drive, designed to do simple things adapted for specific hardware/functions" "What is a real-time operating system - Correct answer Processes data as it comes in - in real time" "Open Source Software - Correct answer Program code made publicly available for free; it can be copied, distributed, or changed without the stringent copyright protections of proprietary software products." "High-level language - Correct answer A programming language like Python that is designed to be easy for humans to read and write." "Interpreter - Correct answer Converts a program written in a higher level language into a lower level language and executes it, one line at a time" "Compiler - Correct answer Translates a high-level source program into machine instructions readable by a processor and saves it to disk. The program executes when run." "Assembler - Correct answer Translates an assembly-language program into machine code" "Stages of compilation - Correct answer lexical analysis - syntax analysis - code generation - optimisation" "Linker - Correct answer Combines together a number of separate object code files." "Loader - Correct answer Loads an executable program into main memory" "Library programs - Correct answer A collection of compiled routines that other programs can use" "Waterfall lifecycle - Correct answer Sequential stages, each stage must be completed for the next to follow - suitable for small projects requiring supervision, drawback that no user involved" "Spiral model - Correct answer Uses structured steps but develops a program iteratively, constantly improving upon a prototype, allows for productive user input as they can comment on a prototype" "Agile modelling - Correct answer Prioritises user participation: keeps model simple and relies on rapid user feedback to make rapid incremental changes, allows for productive user input as they can comment on a prototype" "Extreme Programming - Correct answer Produces frequent project releases in short development cycles, improving productivity and introducing checkpoints, good for large projects to present bogging down" "Rapid Application Development (RAD) - Correct answer A development method that uses workshops/focus groups and an iterative approach to rapidly produce a high-quality system, good for large projects to present bogging down" "Procedural Programming - Correct answer Method of programming that uses step-by-step instructions (encompasses structured programming) supported by python/pascal" "Object-oriented programming - Correct answer A style of programming that involves representing items, things, and people as objects rather than basing the logic around actions, supported by Java, Python, Delphi" "Declarative programming - Correct answer Problem is described, language implementation decides how to solve it eg. SQL" "Functional Programming - Correct answer A programming paradigm that uses functions to create programs. Supported by Haskell, Python, Java" "ADD - Correct answer Add the contents of the memory address to the accumulator" "SUB - Correct answer Subtract the contents of the memory address from the accumulator" "STA - Correct answer Store the accumulator value in the memory address given" "LDA - Correct answer Load the contents of the given memory address into the accumulator" "BRA - Correct answer Branch- use the address given as the address of the next instruction" "BRZ - Correct answer Branch to the given address if accumulator is zero" "BRP - Correct answer Branch to the given address if the accumulator value is positive (or zero)" "INP - Correct answer Input into the accumulator" "OUT - Correct answer Output contents of the accumulator" "HLT - Correct answer Stops the execution of the program" "DAT - Correct answer Indicates a location containing data" "Addressing modes - Correct answer -Immediate addressing -Direct addressing -Indirect addressing -Indexed addressing" "Immediate Addressing - Correct answer The operand is the actual value to be operated on" "Direct Addressing - Correct answer The operand holds the memory address of the value to be operated on" "Indirect Addressing - Correct answer The operand is the location holding the address of the relevant data" "Indexed Addressing - Correct answer Modifies the address in the address field by the addition of a number held in a special-purpose registers, called an index register, before the address is used." "Classes - Correct answer A description of what data looks like and can do: an object is an instance of a class" "Methods - Correct answer Things that objects are coded to do" "Attributes - Correct answer The data associated with an object" "Inheritance - Correct answer Where a class retains the methods and attributes of its parent class as well as having its own" "Polymorphism - Correct answer When subclasses redefine a method or attribute originally inherited from a superclass" "Encapsulation - Correct answer The process of keeping an object's attributes private so they can only be accessed and changed via public methods" "Lossy Compression - Correct answer data compression techniques in which some amount of data is lost - redundant information is eliminated" "Lossless Compression - Correct answer a data compression algorithm that allows the original data to be perfectly reconstructed from the compressed data - no data is lost, file size is still made smaller" "Lexical analysis - Correct answer Comments and whitespace are removed Variables, and subroutines stored in symbol table Which also holds data such as scope and data type Code is converted to a series of tokens" "Syntax analysis - Correct answer The code is checked to ensure it follows the rules of the language. Where it breaks the rules of the language errors are generated. If no rules are broken then it's passed on to the next stage" "Code generation and optimisation - Correct answer Here the object code (accept machine code) is created. (i.e. the binary that is executed by the processor) This code may be inefficient: may contain unnecessary instructions or groups of instructions that can be replaced by simpler ones (point of optimisation)" "Run Length Encoding - Correct answer A compression algorithm that represents an image in terms of the length of runs of identical pixels - lossless" "Dictionary-based compression - Correct answer Uses a dictionary to replace repeated phrases with shorter binary strings - lossless" "Symmetric Encryption - Correct answer An encryption method whereby the same private key is used to encode and to decode the message" "Asymmetric Encryption - Correct answer a type of encryption based on algorithms that require two keys -- one of which is secret (or private) and one of which is public (freely known to others)." "Hashing - Correct answer transforming plaintext of any length into a short code called a hash" "Uses of Hashing - Correct answer -Passwords -Digital signatures -Digital certificates -Hash tables" "Flat file database - Correct answer Database which consists of just one table." "Primary Key - Correct answer A field (or group of fields) that uniquely identifies a given entity in a table" "Secondary Key - Correct answer A field that has some identifying information, but typically does not uniquely identify a record with complete accuracy." "Foreign Key - Correct answer A primary key of one table that appears as an attribute in another table and acts to provide a logical relationship between the two tables" "Composite Key - Correct answer Two or more fields that collectively define the primary key by unique combinations of their values." "First Normal Form (1NF) - Correct answer A table that has a primary key and in which there are no repeating attributes or groups of attributes" "Second Normal Form (2NF) - Correct answer A table in first normal form in which there are no partial dependencies (only relevant if the primary key is a composite primary key)" "Third Normal Form (3NF) - Correct answer A table in 2NF where all attributes are dependent on the key, the whole key and nothing but the key" "SELECT - Correct answer SELECT field(s) FROM table(s) WHERE criteria ORDER BY ascending/descending" "CREATE TABLE - Correct answer CREATE TABLE name ( field datatype )" "ALTER TABLE - Correct answer ALTER TABLE name ADD field datatype ALTER TABLE name DROP COLUMN column ALTER TABLE name MODIFY COLUMN name modification" "INSERT INTO - Correct answer INSERT INTO table_name (columns) VALUES (values)" "UPDATE - Correct answer UPDATE table SET field = new value WHERE condition" "ACID - Correct answer Atomicity, Consistency, Isolation, Durability" "Atomicity - Correct answer Requires that a transaction be processed completely or not at all" "Protocol Layering - Correct answer Simplifying a network's design by dividing them into functional layers, and assigning different protocols to perform each layer's task." "Circuit Switching - Correct answer A switching technique in which one endpoint creates a single path connection to another, depending on the requirement" "Packet Switching - Correct answer Data is split into chunks called packets which have labels including address being sent to and order. Each packet is sent on the most convenient/avoidable route meaning they may arrive in a different order to which they were sent. Once packets arrive at receiver they are reordered." "What is a WAN? - Correct answer Wide Area Network: a network comprised of many LANs to cover a large geographical area" "What is a bus topology? - Correct answer Where computers and other devices in a network are attached to a single backbone Advantage: Inexpensive to install - less cable and specific hardware than a star Disadvantages: low security and reliability because of shared backbone, performance degrades with heavy traffic" "What is a star topology? - Correct answer Where client machines are connected to a central switch or hub, which is usually in turn connected to one or more servers. Signals travel in either direction. Advantages: Consistent performance and more reliable - difficult to derail entire system, transmissions are more private/secure, new stations can be added with minimal disruption Disadvantages: More expensive because more cable is required, single point of failure in central switch" "Physical Topology - Correct answer The physical arrangement of connections between computers." "Logical Topology - Correct answer The logical way computers connect on a network - the shape of the path the data travels in" "What is the TCP/IP model? - Correct answer A set of rules to format a message so it can be sent over a network: four connected layers allow communication to take place - Link Layer - Network Layer - Transport Layer - Application layer" "What does the network layer do? - Correct answer Responsible for addressing and routing of messages" "What does the transport layer do? - Correct answer Responsible for preparing data to be transported across the network" "What does the application layer do? - Correct answer Provides access to network resources" "What does the link layer do? - Correct answer This layer controls the transmission and reception of packets of data to/from a local network" "Firewall - Correct answer A security barrier that controls the flow of information between the Internet and a private network. A firewall prevents outsiders from accessing an enterprise's internal network, which accesses the Internet indirectly through a proxy server." "Proxy Server - Correct answer A server that acts as an intermediary between a user and the Internet." "Consistency - Correct answer No transaction can violate any of the defined validation rules eg. referential integrity must be intact" "Isolation - Correct answer Concurrent execution of transactions leads to the same outcome as if they were to be processed consecutively" "Durability - Correct answer Once transactions are committed, they cannot be undone" "Record locking - Correct answer Restricting access to a record whilst it is being updated to prevent loss of updates/inconsistencies" "Redundancy - Correct answer Storing the same fact in more than one place in case of emergency" "DNS - Correct answer Domain name system - the service that translates URLs to IP addresses." "Client-server network - Correct answer A network that uses centrally administered computers, known as servers, to enable resource sharing for and to facilitate communication between the other computers on the network." "Peer-peer network - Correct answer A network without a central file server and in which all computers in the network have access to the public files located on all other workstations" "html - Correct answer Code within these tags is interpreted as HTML" "body - Correct answer Content in main browser content area" "img - Correct answer The img tag defines an image in an HTML page img src = location, height=x, width=y" "a - Correct answer Defines a hyperlink a href = "location" text /a" "ol - Correct answer Numbered list (ordered list)" "ul - Correct answer Bulleted list (unordered list)" "li - Correct answer A list item (ordered and unordered)" "How does a search engine index a page? - Correct answer A program called a crawler traverses the web taking each word in the document and adding an entry for the page (under the word) in the index alongside the word's position on the page." "Client-side processing - Correct answer Data is processed on a client computer instead of by the server Means source code is visible, allowing it to be modified Reduces unnecessary load on server" "Server-side processing - Correct answer Data is processed by server More secure as client-side validation can be circumvented" "Arrays - Correct answer Finite, ordered set of elements of the same type (static data structure)" "Records - Correct answer A collection of fields that appear as a row in a database or table." "Queues - Correct answer FIFO - new items to the end, elements retrieved from the front" "List - Correct answer An abstract data type consisting of a number of items - allows for an item to occur more than once" "Linked List - Correct answer A dynamic data structure that consists of nodes, where each node contains data as well as a link to the next node, but that does not use contiguous memory." "Stacks - Correct answer LIFO - new items to the end, elements retrieved from the end" "Graphs - Correct answer A set of nodes connected by edges (one or two way)" "Trees - Correct answer Graphs in which there is a root - each node has only one parent" "Distribution - Correct answer X AND (Y OR Z) = (X AND Y) OR (X AND Z) (X OR Y) AND (W OR Z) = (X AND W) OR (X AND Z) OR (Y AND W) OR (Y AND Z)" "Association - Correct answer X AND (Y OR Z) = (X AND Y) OR Z X OR (Y OR Z) = (X OR Y) OR Z" "Commutation - Correct answer X AND Y = Y AND X X OR Y = Y OR X" "Absorption - Correct answer X OR (X AND Y) = X X AND (X OR Y) = X" "Double Negation - Correct answer X = NOT NOT X" "Boolean algebra symbols - Correct answer ∧ AND ∨ OR ¬ NOT" "Half Adder - Correct answer Takes an input of two bits and give a correct result of their addition" "Full Adder - Correct answer Logic circuit with three inputs and two outputs." "D-type flip flop - Correct answer Can store 1 bit of data. Delay data up to one clock pulse. Two inputs: data and clock. Two outputs: delayed data, inverse of delayed data" "Data Protection Act - Correct answer 1998 Data must be processed fairly and lawfully: - Relevant - Accurate - Only used for intended purpose - Secure" "Computer Misuse Act - Correct answer 1990 The act which makes illegal a number of activities such as deliberately planting viruses, hacking, using IT equipment for fraud." "The Copyright Design and Patents Act - Correct answer 1988 Prevents illegal distribution of software - requires adequate licencing Does not apply to algorithms" "The Regulation of Investigatory Powers Act - Correct answer 2000 Enables public bodies to demand information/cooperation from an ISP Existence of warrants and data can not be revealed in court" "Binary Search Tree - Correct answer A binary tree with the property that for all parent nodes, the left subtree contains only values less than the parent, and the right subtree contains only values greater than the parent." "Hash tables - Correct answer Hash tables contain a table with data and a mapping function which assigns each entry a corresponding hash" "De Morgan's Law - Correct answer "not (A and B)" is the same as "(not A) or (not B)" "not (A or B)" is the same as "(not A) and (not B)""