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OCR GCSE Computer Science – Study
Notes & Key Concepts.
comparison operator - <<Answers ✅✅compares two values and outputs either true or false
compiled code - <<Answers ✅✅an executable file created by a compiler
compiler - <<Answers ✅✅a programming tool to translate source code into machine code
compression - <<Answers ✅✅process of making the size of a file smaller
computational thinking - <<Answers ✅✅tackling a problem through decompostion, abstraction and algorithmic thinking
concatenation - <<Answers ✅✅joining strings together
constant - <<Answers ✅✅named value which cannot be altered as program is running
debugging - <<Answers ✅✅identifying and fixing errors in a program
dedicated system - <<Answers ✅✅a computer system designed to carry out a specific task
denary - <<Answers ✅✅system using base- 10
digital signal - <<Answers ✅✅the representation of an analogue signal using binary data
Arithmetic Logic Unit (ALU) - <<Answers ✅✅Performs operations on data e.g. Addition, subtraction
Control Unit (CU) - <<Answers ✅✅Coordinating activities of the CPU
Registers - <<Answers ✅✅Quick, small stores of data within the CPU
Memory Address Register (MAR) - <<Answers ✅✅Holds memory address for data or a instruction about to be used by the CPU
Memory Data Register (MDR) - <<Answers ✅✅Holds actual data or instruction
Accumulator - <<Answers ✅✅Stores results of calculations in the ALU
Program Counter (PC) - <<Answers ✅✅Holds memory address of the instruction for each cycle
Fetch - <<Answers ✅✅The next instruction is retrieved by CPU from main memory
Decode - <<Answers ✅✅The instruction is broken down and decided so computer can understand
Execute - <<Answers ✅✅The CPU performs what the instructions told
Embedded System - <<Answers ✅✅A computer system built within a large device e.g. Camera, washer, car
Volatile - <<Answers ✅✅Memory loses its data when power of
Non-volatile - <<Answers ✅✅Memory retains its data when power is lost
Magnetic storage - <<Answers ✅✅Hard drives
ADV: fast access, stores large amounts of data, low cost
DIS: not very portable, easily be broken
Solid State storage - <<Answers ✅✅USB, flash memory, SD
ADV: fast, small, light, easily potable, quiet
DIS: more expensive, storage capacity less, limited number erase/write cycles
Cloud stotage - <<Answers ✅✅Data is stored on multiple servers in a remote location
ADV: secure, can be accessed anywhere, no need to buy
DIS: needs internet, download and upload can be effected by internet connection, less control if data is held
Operating System - <<Answers ✅✅essential software that links the hardware and other software together and generally manages the computer system
Command-line Interface - <<Answers ✅✅Text commands where user has to type in command
Graphical User Interface (GUI) - <<Answers ✅✅uses icons and other visual indicators to navigate and issue commands
Utility Software - <<Answers ✅✅maintains a computer
Defragmentation Software - <<Answers ✅✅reorganises data on the hard drive to put fragmented files back together and moves files to collect all the free space
Backup Software - <<Answers ✅✅Full Backup - a copy is taken from from every file on the system
Incremental Backup - only files created or edited since last backup are copied
Compression Software - <<Answers ✅✅reduces file size so they take up less space on hard disk
Encryption Software - <<Answers ✅✅scrambles data to stop others from accessing it
Open Source Software - <<Answers ✅✅source code is made freely available and users can modify it
ADV: free, ,made for greater good, can be adapted
DIS: small, buggy, security holes, no warranties, no customer support
Proprietary Software - <<Answers ✅✅only the compiled code is released and the source code is kept a secret
ADV: warranties, well-tested, reliable, cheaper
DIS: expensive, software may not fit user needs
Personal Area Network (PAN) - <<Answers ✅✅within the range of an individual person
Local Area Network (LAN) - <<Answers ✅✅a network that connects devices close to each other e.g. school, house
Wide Area Network (WAN) - <<Answers ✅✅a network within a large geographical area e.g. internet
Bandwidth - <<Answers ✅✅amount of data that can be transferred in a given time
Network Interface Card (NIC) - <<Answers ✅✅allow a device to connect to a network
Switch - <<Answers ✅✅connect devices on a LAN
Router - <<Answers ✅✅responsible for transmitting data between networks
HTTPS - <<Answers ✅✅more secure - encryption
File Transfer Protocol (FTP) - <<Answers ✅✅used to access, edit and move files between devices
Post Office Protocol (POP3) - <<Answers ✅✅used to retrieve emails from a server, holds until download - then deletes from server
Internet Message Access (IMAP) - <<Answers ✅✅used to retrieve emails, server holds until you actually delete it- only download a copy
Simple Mail Transfer Protocol (SMTP) - <<Answers ✅✅used to send emails, used to transfer emails between servers
Layer - <<Answers ✅✅ADV: manageable pieces, self-contained can change without effecting others
Application Layer - <<Answers ✅✅turning data into websites
Transport Layer - <<Answers ✅✅controlling data flow - splitting data into packets
Network Layer - <<Answers ✅✅making connections between networks
Data link Layer - <<Answers ✅✅passing data over physical network-
Domain Name Server (DNS) - <<Answers ✅✅translates websites' domain name into its IP address
Virtual Network - <<Answers ✅✅network that is entirely software based, created by partitioning of some physical network
Blagging - <<Answers ✅✅invented scenario to engage a targeted victim in a manner that increases the chance the victim will divulge information
Phishing - <<Answers ✅✅used to gain personal information for purposes of identity theft, using fraudulent e-mail messages that appear to come from legitimate businesses.
Shouldering - <<Answers ✅✅used to obtain information such as personal identification numbers (PINs), passwords and other confidential data by looking over the victim's shoulder.
Malware - <<Answers ✅✅malicious software - computer programs designed to infiltrate and damage computers without the users consent.
Virus - <<Answers ✅✅program loaded onto a user's computer without the user's knowledge and performs malicious actions. It can self-replicate, inserting itself onto other programs or files, infecting them in the process.
Worm - <<Answers ✅✅program that replicates itself in order to spread to other computers. Often, it uses a computer network to spread itself, relying on security failures on the target computer to access it.
Trojan Horse - <<Answers ✅✅program which misleads users of its true intent.
Spyware - <<Answers ✅✅aims to gather information about a person or organization without their knowledge
Adware - <<Answers ✅✅unwanted advertisements to the user of a computer
Brute Force Attack - <<Answers ✅✅trail and error to gain information
Denial of Service Attack (DOS) - <<Answers ✅✅hacker stop users from accessing a part of a network, flooding network with useless traffic making computer very slow
alphanumeric - <<Answers ✅✅collective name for letters, digits, symbols
analogue signal - <<Answers ✅✅a continuous signal which can't be processed by a computer
argument - <<Answers ✅✅a value that a parameter of a subprogram actually takes
ALU - <<Answers ✅✅part of CPU that carries out arithmetic and Boolean operations
array - <<Answers ✅✅data structure where all data is stored and defined under one variable name
ASCII - <<Answers ✅✅A 7-bit character set consisting of 128 characters
assembler - <<Answers ✅✅a program that turns assembly language into machine code
assembly language - <<Answers ✅✅low-level langauge
authentication - <<Answers ✅✅a process for checking user identity
binary - <<Answers ✅✅a counting system using base-2 consisting of 0s and 1s
binary shift - <<Answers ✅✅moving the bits in a binary number left or right and filling gaps with 0s
BIOS - <<Answers ✅✅Basic Input Output System
bitmap image - <<Answers ✅✅a graphic made up of pixels
bit - <<Answers ✅✅a binary digit either 0 or 1
bit rate - <<Answers ✅✅number of bits used per second of sampled audio
breakpoint - <<Answers ✅✅a programming tool used to halt a program at a specific place
byte - <<Answers ✅✅8 bits
casting - <<Answers ✅✅a way of changing from one data type to another
character - <<Answers ✅✅a single alphanumeric symbol
code editor - <<Answers ✅✅part of an IDE where you write and edit your source code
colour depth - <<Answers ✅✅the number of bits used for each pixel in an image file
comment - <<Answers ✅✅a note added to source code to say what part of a program does
DO WHILE loop - <<Answers ✅✅type of iteration statement
erroneous data - <<Answers ✅✅test data that a program isn't designed to accept
error diagnostics - <<Answers ✅✅information about an error once it is detected
extended ASCII - <<Answers ✅✅an 8-bit character set consisting of 256 characters
GUI - <<Answers ✅✅Allows the user to interact with the computer in a visual and intuitive way
GUI builder - <<Answers ✅✅an IDE tool for giving a program a graphical user interface
hexadecimal - <<Answers ✅✅a counting system using base-16 consisting of 0-9 digits and letters a-f
high-level language - <<Answers ✅✅A programming language like C++ or Java
IF statement - <<Answers ✅✅type of selection statement
indentation - <<Answers ✅✅Spaces put at the beginning of a line of code to help show a programs structure
input sanitation - <<Answers ✅✅removing unwanted characters from an input
input validation - <<Answers ✅✅Checking that an input meets a certain criteria
integer - <<Answers ✅✅A numerical data type for whole numbers
interpreter - <<Answers ✅✅A translator that turns source code into machine code
iteration statement - <<Answers ✅✅A statement which make a program repeat a series of instructions
iterative testing - <<Answers ✅✅Repeated testing done during the development of a program
kilobyte - <<Answers ✅✅1024 bytes
linker - <<Answers ✅✅a program tool which can combine codes
local variable - <<Answers ✅✅a variable that is only defined and useable within certain parts of a program
logic circuit - <<Answers ✅✅An electronic circuit for performing logic operations on binary data
logic error - <<Answers ✅✅when a program does something that was not intended
logic gate - <<Answers ✅✅an electronic circuit component that performs a Boolean operation
loop - <<Answers ✅✅A set of instructions that repeat until a condition is met
lossless compression - <<Answers ✅✅Temporarily removing a file to decrease file size
lossy compression - <<Answers ✅✅permanently removing a file to decrease file size
machine code - <<Answers ✅✅the lowest level of programming language formed of 1's and 0's
maintainability - <<Answers ✅✅a characteristic of a defensive design that helps programmers modify their creation
megabyte - <<Answers ✅✅1024 kilobytes
metadata - <<Answers ✅✅extra data stored in a file which gives information about the file's properties
sequences - <<Answers ✅✅only one way from start to finish
selections - <<Answers ✅✅multiple ways to get from start to finish
iterations - <<Answers ✅✅loops that allows to repeat a task
exponentiation - <<Answers ✅✅raise a number to a power
DIV operator - <<Answers ✅✅returns whole number part of division
MOD operator - <<Answers ✅✅returns remainder part of division
== - <<Answers ✅✅is equal to
<> or != - <<Answers ✅✅is not equal to
< - <<Answers ✅✅is less than
- <<Answers ✅✅is greater than
<= - <<Answers ✅✅is less than or equal to
= - <<Answers ✅✅is greater than or equal to
comparison values - <<Answers ✅✅produce boolean value
x.upper - <<Answers ✅✅changes all characters in string x to upper case
x.lower - <<Answers ✅✅changes all characters in string x to lower case
x.length - <<Answers ✅✅returns number of character in string x
x[i] - <<Answers ✅✅extracts the character in position i from string x
x.subString(a,b) - <<Answers ✅✅extracts string starting at portion a with length b from string x
switch-case statements - <<Answers ✅✅check value of a variable
for loops - <<Answers ✅✅example of a count-controlled loop
AND - <<Answers ✅✅&&
OR - <<Answers ✅✅| |
NOT - <<Answers ✅✅!
element - <<Answers ✅✅each piece of data inside array
records - <<Answers ✅✅rows of tables in databases - store a category
fields - <<Answers ✅✅columns of tables in databases - story details about specific item
primary key - <<Answers ✅✅uniquely identifies record in table (database)
data values in same record - <<Answers ✅✅have different data types
FROM - SQL command - <<Answers ✅✅tells database which tables to look in
WHERE - SQL command - <<Answers ✅✅specifies condition that a record must satisfy before it is returned
WHERE with AND and OR - SQL command - <<Answers ✅✅makes search more specific
WHERE with LIKE - SQL command - <<Answers ✅✅searches for a pattern
LIKE - SQL command - <<Answers ✅✅% used to represent any combination of letters and numbers
ORDER BY - SQL command - <<Answers ✅✅sort records into ascending (ASC) or descending (DESC) order
parameters - <<Answers ✅✅special variables used to pass values into a sub program (specify name, data type, default value)
arguments - <<Answers ✅✅actual values that parameters take when sub program called
total number of colours - <<Answers ✅✅2^n (where n = number of bits per pixel)
24 bit colour depth - <<Answers ✅✅average device colour depth
resolution - <<Answers ✅✅density of the pixels in an image
bit rate equation - <<Answers ✅✅sampling frequency x sample size
range check - input validation - <<Answers ✅✅checks the data is within a specified range
presence check - input validation - <<Answers ✅✅checks data has been entered
check digit - input validation - <<Answers ✅✅checks numerical data has been entered accurately
format check - input validation - <<Answers ✅✅checks data has correct format
look-up table - input validation - <<Answers ✅✅checks data against a table of acceptable values
length check - input validation - <<Answers ✅✅checks data is correct length
syntax errors - <<Answers ✅✅rules or grammar of programming language is not followed so compiler or interpreter doesn't understand
logic errors - <<Answers ✅✅when compiler or interpreter is able to run program but program does something unexpected
diagnosing logic errors - <<Answers ✅✅found through general use of program and by systematically testing
performance test - <<Answers ✅✅tests how quickly certain features run and their impact on computer resources
usability test - <<Answers ✅✅tests how user-friendly the interface and features are
security test - <<Answers ✅✅tests vulnerability to attacks and how securely data is stored
