Download Binary Number Systems and Data Representation in Computer Science: A Comprehensive Guide and more Exams Nursing in PDF only on Docsity!
GCSE Edexcel Computer Science
actual solution
Explain how binary is used to represent data (numbers, text, sound, graphics) and program instructions - answer -binary is used to represent all elements in a computer It is stored as a series of 0s and 1s These relate to the position of transistors (on or off) All analogue data stored is converted into digital (binary) Explain the difference between unsigned and signed integers - answer -An unsigned integer can only represent positive values A signed integer can represent positive and negative values Both unsigned and signed integers are as accurate Both unsigned and signed integers can have overflow errors Unsigned integers store more positive values (unsigned is 0 to 255, signed is - to 127) Both unsigned and signed integers use a parity bit Parity bits are used to check the binary value transmitted is correct Explain how sign and magnitude is used to represent positive and negative values 0 - answer -Explain how sign and magnitude is used to represent positive and negative values
Explain how 2's complement is used to represent negative values - answer -To convert a binary value into two's complement ...flip the value of each bit (0 becomes 1, 1 becomes 0) Add 1 to the flipped value Explain how to convert from binary to denary (decimal) - answer -Write out the headings for the binary value, starting with 1 on the right-hand side ...usually finishing at 128 ...add up the headings with 1 values beneath them Explain how to convert from denary (decimal) to binary - answer -Write out the headings from 1 to 128, starting on the right-hand side ...assume the denary value you are converting is an amount of money ...You want to purchase the most expensive headings you can ...remember to calculate the remainder (subtraction) ...if you can purchase a heading it gets a 1 below it ...if you cannot purchase a heading it get a 0 below it ...when you finish you should have no money left Explain how to add two binary values together - answer -Four rules that need to be followed to add binary values ...0 + 0 = 0 ...1 + 0 = 1
Hexadecimal is only used by humans as computers only ever use binary Explain how computers encode characters using ASCII - answer -Each character has a unique binary code This unique code is sent by the keyboard to the computer The ASCII code for A is 65 (in binary 0100 0001) Codes for other binary numbers can be found from A (B is 66, C is 67, D is 68, etc) ASCII codes for letters are always represented as 8 bit binary values (e.g. 0100
Explain the difference between ASCII and UNICODE - answer -ASCII can represent 127 different characters ...the 8th bit it used as a checksum UNICODE uses 16 bit instead of 8 bit ...this means it can represent 65,536 different characters ...this can include elements from other languages, symbols, and maths characters Explain what pixels are (in relation to bitmap images) - answer -Pixels are the smallest elements of a bitmap image and the smallest parts that can be displayed on a screen Explain what resolution is (in relation to bitmap images) - answer -The resolution of an image is based on the number of elements used to represent the full image ...the higher the number of elements for a given size, the better the quality of the image
Resolution is the number of pixels per inch when the image is displayed (on a monitor, or on paper) Explain what colour depth is (in relation to bitmap images) - answer -Colour depth indicates the number of bits used to represent the colour of a picture element ...the higher the number of bits used, the greater the range of colours Explain what RBG colour is and how it works - answer -All colours are combinations of RGB (red/green/blue) An equal number of bits is usually given to each colour Explain how bitmap image file sizes are calculated - answer -Bitmap image files are a combination of image size and colour depth Bitmap image files are calculated by using width x height x colour depth The better the image quality the larger the file size Explain how sound (an analogue signal) is represented in binary - answer -The amplitude of the signal is recorded digitally This is done at regular intervals, which is the sample frequency The greater the sample frequency the more samples ...the smoother the digital representation of the original audio ...this results in less distortion of the original audio ...this makes the resulting digital representation more accurately match the original audio
Explain how lossy compression can be acceptable for audio compression - answer - Lossy compression for audio can be acceptable because most people do not notice ...most people have a limited hearing range ...sounds (frequencies/amplitudes) can be masked by other sounds ...people's brains will 'fill in the blanks' Explain the advantage of compressing files - answer -Compressed files will reduce the amount of space needed to store the file Compressed files will mean the file will take less time to download Explain how run - answer -length encoding (RLE) works - runs of a single colour are compressed to a single item and a count of that item rrrgbbb would become 3r1g3b Explain why run - answer -length encoding (RLE) may not always be suitable - RLE may not be suitable if as it might increase the file size ...or the file may not be compressed very much/at all ...if characters s are distributed randomly/not repeated/no runs of similar characters are found Explain how file size is measured and how file sizes are calculated - answer -Files on computers are always stored in bytes To calculate the size of a file the number of bits used needs to be counted This can then be divided by 8 to convert to bytes ...and then by 1024 to move between other units
Explain the need for data encryption - answer -Encryption prevents unauthorised reading/use/analysis of sensitive/payment/personal data Explain how a Caesar cipher algorithm work - answer -Explain how a Caesar cipher algorithm work / Each letter in the plaintext is 'shifted' a certain number of places down the alphabet For example, with a shift of 1, A would be replaced by B, B would become C, Z would become A Shifts can be positive and negative ...a negative shift is a shift to the right (moving backwards) ...a positive shift is a shift to the left (moving forwards) Explain the differences between structured and unstructured data - answer - Unstructured data is data that is not organised ...this includes emails, images, uploads to social networking sites Unstructured data is not ordered into categories ...this makes it difficult to be linked and searched Structured data is data that is organised and ordered so information can be retrieved quickly Structured data also allows links to be made to create information ...this allows it to be searched or queried quickly ...an example of this would be a dictionary in alphabetical order, or a list of numbers from smallest to largest
Explain what an attribute is (in relation to databases) - answer -Attributes are the set of properties used to describe instances of an entity Attributes are items of data that can be stored about an entity Explain what a key field is (in relation to databases) - answer -A key field is sued to identify each record ...and must contain unique data Explain what a foreign key is (in relation to databases) - answer -A foreign key is a field containing the primary key from another table ...this allows the tables to be linked together Explain how a database can be used to model a real life situation - answer -A table represents a single real-life entity (e.g. hotel guest, hotel rooms, hotel staff) Tables are made up of fields (headings) and records (entries) A record is an entry in a table (e.g. each guest would have their own record) A field is an attribute for the entity (e.g. name, address, date of birth, length of stay) A primary key is a unique field in each record A primary key ensures that no two records could ever be exactly the same Explain the input process output model - answer -Data is entered and manipulated according to the instructions of the program The results of the processing are then displayed to the user in a suitable form
Explain what the function of the CPU - answer -The Central Processing Unit (CPU) executes all of the stored program instructions Explain the function of Main Memory - answer -Main memory is used to store all program instructions and data All programs being executed (or due to be) must be held in RAM Explain the function of Cache - answer -Cache memory sits between the CPU and Main Memory (RAM) Cache memory reduces the need to access instructions and data from main memory Cache memory makes up for the speed difference between the CPU and Main Memory Give the three main storage types and an example of each one - answer -Magnetic storage example is hard drive Optical storage examples are CDs and DVDs Solid state examples are USB sticks and Solid-State Hard Drives Explain what peripherals are - answer -Peripherals are any device connected to a computer These include input devices (keyboard, mouse) and output devices (printer, monitor)
...this is known as the opcode One type of information in a binary sequence is data ...this is known as the operand They combine to become the two things stored in main memory in the Von Neumann model Explain what the control unit does (as part of the FDE cycle) - answer -The control unit coordinates the actions of the computer ...by sending out control signals to other parts of the CPU and components Explain what the arithmetic logic unit (ALU) does (as part of the FDE cycle) - answer -The Arithmetic Logic Unit (ALU) performs all arithmetic and logic functions ...including addition, subtraction, comparisons between two different numbers Explain what clock speed is - answer -The CPU carries out one instruction each clock cycle The clock speed is the number of cycles per second It is measured in Hertz (Hz) Explain what the four different registers in the CPU are and what each one does - answer -There are four different registers used by the CPU The Program Counter holds the address of the next instruction to be fetched The Memory Data Register (MDR) is a temporary store for anything copied from memory
The Memory Address Register holds the address of the memory location currently being read or written to The Accumulator store the results of calculations carried out by the ALU Explain how data is stored on magnetic devices - answer -Explain how data is stored on magnetic devices Explain how data is stored on optical devices - answer -Optical storage comprises of small pits are burned in patterns onto a flat surface ...a laser can be used to interpret light reflected from the flat or pitted surface Explain how data is stored on solid state devices - answer -Solid State Drives uses NAND (memory) Solid State Drives are arranged in a grid (columns/rows) In Solid State Drives if a set of transistors are charged, then this represents a 1 In Solid State Drives if a set of transistors are uncharged, then this represents a 0 Explain the advantages and disadvantages of cloud storage - answer -Cloud storage can be cheaper as you do not need to buy your own hardware Cloud storage can be accessed from any internet device Cloud storage can be easily scaled (larger or smaller) to meet your needs Cloud storage can be more expensive if you have lots of data to store Cloud storage speed is limited by your bandwidth Cloud storage means a third party is keeping your data
Explain how to construct a truth table for a NOT gate - answer - Explain what the terms AND, OR and NOT mean in a logic statement - answer -AND means both statements/events are true/need to happen OR means that either statement/even can be true/need to happen NOT means that the statement/event does not happen Explain the functions of an Operating System (OS) - answer -An OS manages files ...providing a structure and system/directories for the management of files An OS allows files to be manipulated (saved, renamed, moved, copied and deleted) An OS manages processes ...allocating/sharing processor time/resources to running programs An OS manages memory ...assigning (blocks of) memory to running programs as required An OS manages hardware/drivers ...to receive data from input devices and to send processed data to output devices Explain how an Operating System (OS) manages files - answer -An OS organises of files in a hierarchy/tree structure A node is either a folder/directory/sub-folder/sub-directory or the file itself The top node/folder/directory/drive is the root
Explain what a user interface is and the different types that can be used - answer - A User Interface allows the user to communicate with the computer A Graphical User Interface (GUI) uses a pointer to select from menus and icons A Command Line Interface (CLI) uses typed commands to input actions Explain the different levels of access that files can be set to - answer -Files can be set as read only, write or no access Write access allows the user to see the contents and make changes to the file Read only access prevents the user accidentally changing/deleting any data No access stops a user seeing any sensitive/irrelevant information No access prevents a user from sharing data (outside of an organisation) Explain what utility software is (as part of an OS) - answer -Utility software can be used to repair files Utility software can include compression, which reduces file sizes Utility software can include defragmentation, which organises file blocks to be stored together Utility software can include backup, which makes an archived copy of data Utility software can include antivirus, which prevents viruses from infecting files Utility software can include firewall, which blocks unwanted network/internet connections Explain what virtual memory is - answer -Virtual memory is used when there is no more physical memory left
Explain what backing up is and the difference between a full and incremental backup - answer -Backing up involves the copying of data stored on a computer system into a separate storage device A full backup all of the data on the storage device is copied An Incremental backup only the new or changed data is copied Explain what fragmentation is and what defragmentation does - answer - Fragmentation is when parts of files are saved in different locations on the storage medium ...this may be due to free space left by other files or the space or the size of the data Defragmentation involves reorganising files by putting pieces of related data back together again ...which means that less disc accesses are needed to read the data ...this improves the performance of the computer Explain what a virus is and how an antivirus program works - answer -A virus is a computer program hidden inside another program with malicious intent Antivirus software is used to scan all files and remove any attached viruses ...using a list of defined viruses Explain what malware is and how an anti-malware program works - answer - Malware is software that has been designed to gain unauthorised access to a computer ...either to disrupt its functioning or collect information
Anti-Malware programs scan for malware using a database of known malware definitions Explain why both antivirus and anti-malware need to be regularly updated - answer -Explain why both antivirus and anti-malware need to be regularly updated Both Antivirus and Anti-Malware need to be constantly updated ...to ensure they have the most up to date list of possible viruses and malware programs Give examples of application software and what each one is used for - answer -One example of application software is a spreadsheet ...this could be used by a biologist to model the behaviour of colonies Image Editing - Cropping images for insertion into a presentation Live Chat - For getting technical support help from a vendor support site Web Browser - For looking up the address of a colleague at a different university Presentation -- Showing results of his research to colleagues at a conference Video Editing -- Creating a video to put on YouTube of his lectures for his students Give examples of application software and what each one is used for Explain what computer modelling is - answer -Computer modelling attempts to abstract the rules and mechanisms that control real life systems Computer modelling allows those systems to be simulated ...these can be under different conditions and used to answer 'what if' questions Computer modelling examples include flight simulators, traffic flow and financial modelling
