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Computer Science - Paper 2 - Part 2 (Size of Numbers (✮Bit, ✮Nibble, ✮Byte…
Computer Science
- Paper 2 - Part 2
Image Representation
Bitmap
✮Made up of pixels (picture elements)
✮Each Colour is represented by a binary code
✮The number of colours is related to the number of bits in the code
✮Increasing the number of bits per pixel increases will increase the range of colours and shades
Colour Depth
✮Number of bits per pixel
✮Total number of colours = 2^n (n= number or bits per pixel)
✮File size = image resolution x colour depth = width x height x colour depth
Sound Sampling
✮Analogue signal is recorded with a microphone
✮They are converted by an ADC (analogue to digital converter)
✮They must be a digital signal for a computer to be able to read them
✮This is called sampling ^
Storage calculations
✮Bit = W x H x C
✮Byte = (W x H x C)/8
✮Kilobyte = ((W x H x C) /8) /1000)
Von Neumann Architecture
Info
✮Describes a system where the CPU runs programs stored in memory
✮Programs consist of instructions and data, stored in memory address
✮Main feature - It only uses one memory for both data and instructions
How it works
✮Computers before Von Neumann only had one function/process. To make them do something else they needed rewiring
✮Von Neumann computers use one memory for both instructions and data
✮Executes programs by doing one instruction after the next using the fetch-decode-execute cycle
Ethics and Morals
Info
✮Ethics = Things considered right and wrong in society
✮Law = what is really right and wrong
✮Environmental issues =how we impact the natural world
Cyberbulling
✮Done to deliberately intimidate, insult or humiliate
✮Can drive people to suicide or cause serious distress
Trolling
✮When some tries to cause a public argument
✮Making comments which frustrate people
✮Tolls usually do this for their own amusement or to gain attention
Ethical problems
✮Smartphones - neglected face-to-face interaction
✮Wearable technology - invasion of privacy possibly
✮Computer based implants - could be expensive and less privacy/ invasive
✮The Digital Divide as some people don't have access - they are at a disadvantage
Computational Thinking
Abstraction
✮Taking away or removing unnecessary detail from a problem
Decomposition
✮Breaking the problem into a number of sub problems so that each sub problem accomplishes an identifiable task
Creating programs (ACE)
✮Accuracy - does it do what it's meant to do?
✮Consistency - does it do it every time?
✮Efficiency - does it do it quickly?
Unicode
✮It is an international coding language to reference every character
Examples:
✮A = U+0041
✮B = U+0042
Boolean Expressions
AND
OR
NOT
XOR
Binary, denary and hexadecimal conversions
✮Binary, the sequence is: 128, 64, 32, 16, 8 ,4, 2, 1 left to right
✮To find the hexadecimal value: divide the value by 16, round down, find the remainder.
Law
Data protection law
✮Data should be kept safe a secure
✮The right of the individual must be observed
✮Data should not be kept longer than than needed
✮Data must be accurate and kept up to date
✮Data should be relevant, adequate and not excessive for the specific use
✮Data must be used for the specific purpose
✮Data must only be used in a fair and lawful way
✮Data should not be transferred abroad without adequate protection
Computer Misuse Act
✮Introduced to stop hacking and and cyber crime
Cyber Crime
✮Any illegal activity that involves computers
Size of Numbers
✮Bit
✮Nibble
✮Byte
✮Kilobyte
✮Megabyte
✮ Gigabyte
✮Terabyte
✮Petabyte
✮Exabyte
✮Zettabyte
✮Yottabyte
ASCII
American Standard Code
A = 65 = 01000001
a = 97 = 01100001
space = 32 = 00100000
Data structures and Types
Structures
✮Defines the flow of data
✮1D array
✮Holds related data as a single item, static or dynamic
2D array
✮Arrays are mutable (can be changed)
✮Record
✮Tuples
Tuples are immutable (cannot be changed)
✮Class
✮A description of an object
Data types ≠ Data structures
Types
✮Interger
Real (float)
✮Boolean
✮String
✮Character
Error Syntax and Runtime
✮ A syntax error is when the compiler/ interpreter doesn't understand what has been typed (doesn't follow the rules of grammar of the language)
✮Logic Error is when the compiler/ interpreter can run the program but it does some thing unexpected
✮ A runtime error is when it is asked to do something it cannot do resulting in a crash (also called an execution error) e.g asking to divide by 0
