a sequence of steps that can be followed to complete a task
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computer program
an implementation of an algorithm
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binary
base 2
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denary
base 10
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hexadecimal
base 16
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why do computers use binary?
easy to represent,
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bit
a single binary digit
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nibble
4 bits
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byte
8 bits
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why do we use hexadecimal in computing?
it is easier for humans to read than binary
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left binary shift
multiplies a number
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right binary shift
divides a number
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what do binary shifts do?
multiplies/divides a number by 2
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how many bits are used to encode in ASCII?
7 bits
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how many bits are used to encode in unicode?
16 bits
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advantages of ASCII
takes up less space
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advantages of unicode
can encode more characters eg in other languages
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how many codes are the same in ASCII and unicode
the first 127
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pixel
picture element
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bitmap image
made up of pixels
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vector graphics
shapes are used to represent an image
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colour depth
number of bits used to represent each pixel
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image file size calculation in bytes
height x width x colour depth /8
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what are vector graphics better for?
artificial images
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what are bitmap images better for?
representing more complex images or natural landscapes
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amplitude
the maximum displacement of a wave
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frequency
the number of cycles per second
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sample
measure of amplitude at a given point in time
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sample rate
number of samples taken per second
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sample resolution
the number of bits used to represent each sample
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sound file size calculation in bytes
length x sample rate x sample resolution
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how are sound waves converted from analogue to digital sound?
the signal is sampled at regular intervals, the samples are approximated, each integer is encoded as a binary number with a fixed number of bits
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huffman coding
a lossless compression method based on how frequently a piece of data occurs
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lossless compression
no data is lost and the file can be decompressed with all of tis information intact
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data compression
storing a file using less memory
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lossy compression
some data is lost when the file is compressed
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huffman compressed file size
total bits x frequency of each character x 7 bit ASCII
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run length encoding (RLE)
reduces the physical size of repeating strings into two bytes
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what are the two bytes in RLE
byte 1 : represent the number of characters in a run byte 2 : the value of the character in the run
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advantage of RLE
good when there are long runs of repeating characters
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analogue
data which can use any value in a continuous range
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software
computer programs that give instructions to the computer to run
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application software
a program designed to perform a specific task that the user interacts with directly
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system software
controls the computer hardware and manages the application software
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network
two or more computers that are connected together
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the internet
a global network of interconnected computers, refers to the hardware
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world wide web
a service that has web pages and other data
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LAN
local area network
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WAN
wide area network
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PAN
personal area network
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advantages of a network
can share resources, allows communication, allows easier network
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disadvantages of a network
greater security risk, malware can spread more easily, if there is a problem it can affect the whole network
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personal area network
set up around an individual person
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example of a PAN
bluetooth
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local area network
covers a relatively small geographical area
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wide area network
covers a much wider geographical area, made up of many local area networks
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WLAN
wireless local area network
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wireless access point (WAP)
a switch that allows devices to connect wirelessly
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Boolean logic
a data type with two values, true or false
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what makes up logic gates
transistors
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logic gates
form the basis of decision making in a computer
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NOT gate
outputs the opposite of the input
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AND gate
only true if both inputs are true
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OR gate
true if either of the inputs are true
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XOR gate
only true if one of the inputs is true not both
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von Neumann architecture
the design of a CPU created by von Neumann in 1945
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stored program concept
where program instructions and the data to be processed are stored in the same memory system
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Arithmetic logic unit (ALU)
where arithmetic and logic operations take place
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Control unit (CU)
controls and monitors data transfer between different input and output hardware and decodes machine code
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Clock
keeps the CPU components synchronised
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Central Processing unit (CPU)
controls the interpretation and executuon of instructions in a computer
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bus
wires through which data is transferred
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registers
memory locations in the CPU used to store frequently accessed data and instructions
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data bus
carries data between components
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address bus
carries the memory address to find the next instruction
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control bus
carries instructions from the CPU
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instruction set
a set of commands for the CPU that tells it how to perform arithmetic and logic operations, handle data and read/write to memory, and control the flow of code
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fetch execute cycle
fetch, decode, execute
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RAM
random access memory
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is main memory volatile
yes
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volatile memory
the content is erased when the computer is turned off
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ROM
read only memory
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is secondary storage volatile
no
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BIOS
basic input output system
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what does BIOS do
tells the CPU to perform self checks and set up the computer by testing the memory, checking what hardware is present and coping the operating system into the RAM
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main memory
where all data, files and programs are stored while they are being used
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which memory type can be read and written to
RAM
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secondary storage
used to save files and holds software like the operating system
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Magnetic hard disk drive (HDD)
tracks with tiny magnets, the polarity of the magnets determines the binary digit, concentric rings of magnets
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advantage of HDD
cheap
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disadvantages of HDD
moving parts can break, electromagnetic surge could corrupt data, slow speed of read/write access
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optical disk (CD)
track with pits and land, uses a laser to read data
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advantage of optical disk
can transfer easily between computers
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disadvantages of optical disk
can scratch easily, not much storage, no unlimited writes
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solid state drive (SSD)
uses transistors with electrons
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advantages of SSD
much faster, reliable when reading, quiet
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disadvantages of SSD
more expensive, less reliable when writing
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operating system
most important piece of system software
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what does the operating system do
manages the processor, memory, input/output devices, applications and security
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disk defragmentation
organises files on a disk to be located contiguously
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