DATA STORAGE
- Bit: Binary digit
- Binary: base 2 system where each digit is a 0 or a 1
Headings are all squares of 2 up to 28
Maximum value is 255
- Denary: base 10 number system using digits 0 to 9 (standard number system 1,2,3,4,5)
- Hexadecimal (Hex): base 16 number system which consists of numbers 0-9 and letters
A-F substituting numbers 10-5; 15 = F
Conversion from binary to denary and vice versa (Add 1s in columns)
Conversion from hexadecimal to binary and vice versa (split into half-bit)
Conversion from hexadecimal to denary and vice versa (first part x16 then add
second part)
Addition of binary digits ( 1 + 1 = 0, carry the one ), ( 1 + 1 + 1 = 1, carry the one)
Binary shifts (→ RIGHT = HALVED, ← LEFT = DOUBLED) and loss of precision
- Overflow: too many digits to fit in a given numbers of bits, these are to be put in brackets
- MSB: Most significant bit LSB: Least significant bit
- Data capacity = Number of data x size then convert into relevant units
CHARACTERS
Every character is represented by a unique binary code
- Character set: collection of characters and their associated unique binary codes which
can be represented by a computer (the characters a computer understands)
- ASCII: American Standard Code for Information Interchange
ASCII uses 7 bits: 27 , so 128 possible characters available
- Unicode: International encoding for different languages such as
Unicode uses 16 bits: 216 so 1,112,064 possible characters available
Unicode also uses 32 bits: 232 so 4,294,967,296 possible characters available
It is able to represent more characters than ASCII as there are more unique binary
codes available for them as it uses more bits
ASCII encodes symbols, digits and letters whereas Unicode encodes special
letters e.g. Egyptian hieroglyphics, emojis
- How are words represented in ASCII: Each character in a word has a unique ASCII code
that represents it which is then converted into a 7-digit binary number
- ASCII vs Extended ASCII
Extended ASCII uses more bits
Extended ASCII represents more characters
Extended ASCII can represent European symbols and different languages
IMAGES
- Pixel Element (Pixel) : Smallest unit of an image.
- Each pixel is allocated one colour only which is encoded by a unique binary code
- Greyscale: Pixels are only shades of grey
- Colours:
2 bits can represent 4 colours (22)
3 bits can represent 8 colours (23)
4 bits can represent 16 colours (24)
, - Colours are on an RGB scale: Red Green Blue
- Metadata: image data about the image (data about the data file) e.g. colour depth, file
size, creator of image, resolution
- Colour depth: the number of possible colours available for a pixel, controlled by the
number of bits the image uses → 3 bits can represent 8 colours (23)
Higher colour depth → Higher number of colours available → higher image
quality → higher file size as more bits are needed per pixel
- Resolution: number of pixels displayed per unit area, commonly measured dots per inch
(DPI)
More DPI → Greater detail stored in image so it can be enlarged without
becoming pixelated
Higher resolution → Higher number of pixels per unit area → Higher number of
bits needed → higher file size
- Image size: number of pixels an image contains (height x width)
- Image file size: Image size x colour depth
SOUND
Vibrations are analogue; they can take any value
- To store sound on a computer, continuous analogue data needs to be converted into
discrete (distinct) digital data. This is done by sampling analogue data then converting it
into binary numbers.
- The height of the wave is sampled at regular intervals and this analogue data is
converted into distinct digital binary data
-
- Q: How is sound stored? [3]
Sample the amplitude of the wave at regular intervals. The measurements taken are
then converted into binary data.
- Q: How does the sample interval affect file size?
The smaller the interval, the more data points collected, the bigger the file size.
- Continuous wave → digital square wave
- Sample rate: number of times per second analogue sound is sampled
Usually measured in Hertz (Hz): 1 sample = 1Hz
Higher sample rate → Higher file size (more data stored) → Higher playback
quality
The length of an audio has no effect on playback quality, it only increases file size
- Sample interval: time in between samples
Decreasing sample rate means the sound will run faster, therefore sample rate
will increase
This is inversely proportional to sample frequency/rate
, - Bit depth: the number of different measurement values that can be stored (number of
bits used to store each sampled value) higher bit depth = more different values you can
measure
More bits → Higher accuracy to original sound → larger file size
- Higher sample rate + Higher bit depth → better approximation to original sound
The analogue sound from the speaker is sampled at a certain number of times per second. This
sampled data is then converted into discrete digital, binary data and stored on the computer
Higher sampling rate means higher number of analogue samples taken per second to be
converted into discrete digital data and stored. More analogue data stored means higher
playback quality as it would mean better approximation to original audio. More data stored
additionally means higher file size.
COMPRESSION
When large amounts of data are transmitted across the internet, it can be slow and expensive. If
data must be stored on a device with limited memory, it must be compressed to reduce
bandwidth and transmission times between devices and create space for more files to be
stored.
- Bandwidth: measure of data transfer rate or data capacity of a medium over a given
period of time
- Lossy compression: where some data is permanently removed to make the file smaller
Removed data is that least likely to be noticed by the human senses e.g. certain
frequencies of band sound inaudible to humans are discarded + large areas of similarly
coloured pixels are combined into one block of the same colour + video files where some
frames may be lost
The image still looks similar to the original
- For files like programs which only work with their full instructions or text which is only
legible with all characters present and in order, Lossless compression is more suitable
- Lossless compression: where a file is compressed without any original information being
lost
This involves storing enough data and information to be able to recreate the
original file exactly at decompression
The computer creates a dictionary of words used and a list providing their original
order
By referring to the dictionary, the original sequence can be reproduced
Storing the index and sequence requires a smaller file than storing the original
This way, files can be restored to their original condition without any data being
lost
SYSTEM ARCHITECTURE
A computer system is made up of hardware and software working together to process data
- The Central Processing Unit (CPU): made up of billions of transistors (small ‘on-off’
switches). It is the most important hardware in a computer and its main functions are
- Bit: Binary digit
- Binary: base 2 system where each digit is a 0 or a 1
Headings are all squares of 2 up to 28
Maximum value is 255
- Denary: base 10 number system using digits 0 to 9 (standard number system 1,2,3,4,5)
- Hexadecimal (Hex): base 16 number system which consists of numbers 0-9 and letters
A-F substituting numbers 10-5; 15 = F
Conversion from binary to denary and vice versa (Add 1s in columns)
Conversion from hexadecimal to binary and vice versa (split into half-bit)
Conversion from hexadecimal to denary and vice versa (first part x16 then add
second part)
Addition of binary digits ( 1 + 1 = 0, carry the one ), ( 1 + 1 + 1 = 1, carry the one)
Binary shifts (→ RIGHT = HALVED, ← LEFT = DOUBLED) and loss of precision
- Overflow: too many digits to fit in a given numbers of bits, these are to be put in brackets
- MSB: Most significant bit LSB: Least significant bit
- Data capacity = Number of data x size then convert into relevant units
CHARACTERS
Every character is represented by a unique binary code
- Character set: collection of characters and their associated unique binary codes which
can be represented by a computer (the characters a computer understands)
- ASCII: American Standard Code for Information Interchange
ASCII uses 7 bits: 27 , so 128 possible characters available
- Unicode: International encoding for different languages such as
Unicode uses 16 bits: 216 so 1,112,064 possible characters available
Unicode also uses 32 bits: 232 so 4,294,967,296 possible characters available
It is able to represent more characters than ASCII as there are more unique binary
codes available for them as it uses more bits
ASCII encodes symbols, digits and letters whereas Unicode encodes special
letters e.g. Egyptian hieroglyphics, emojis
- How are words represented in ASCII: Each character in a word has a unique ASCII code
that represents it which is then converted into a 7-digit binary number
- ASCII vs Extended ASCII
Extended ASCII uses more bits
Extended ASCII represents more characters
Extended ASCII can represent European symbols and different languages
IMAGES
- Pixel Element (Pixel) : Smallest unit of an image.
- Each pixel is allocated one colour only which is encoded by a unique binary code
- Greyscale: Pixels are only shades of grey
- Colours:
2 bits can represent 4 colours (22)
3 bits can represent 8 colours (23)
4 bits can represent 16 colours (24)
, - Colours are on an RGB scale: Red Green Blue
- Metadata: image data about the image (data about the data file) e.g. colour depth, file
size, creator of image, resolution
- Colour depth: the number of possible colours available for a pixel, controlled by the
number of bits the image uses → 3 bits can represent 8 colours (23)
Higher colour depth → Higher number of colours available → higher image
quality → higher file size as more bits are needed per pixel
- Resolution: number of pixels displayed per unit area, commonly measured dots per inch
(DPI)
More DPI → Greater detail stored in image so it can be enlarged without
becoming pixelated
Higher resolution → Higher number of pixels per unit area → Higher number of
bits needed → higher file size
- Image size: number of pixels an image contains (height x width)
- Image file size: Image size x colour depth
SOUND
Vibrations are analogue; they can take any value
- To store sound on a computer, continuous analogue data needs to be converted into
discrete (distinct) digital data. This is done by sampling analogue data then converting it
into binary numbers.
- The height of the wave is sampled at regular intervals and this analogue data is
converted into distinct digital binary data
-
- Q: How is sound stored? [3]
Sample the amplitude of the wave at regular intervals. The measurements taken are
then converted into binary data.
- Q: How does the sample interval affect file size?
The smaller the interval, the more data points collected, the bigger the file size.
- Continuous wave → digital square wave
- Sample rate: number of times per second analogue sound is sampled
Usually measured in Hertz (Hz): 1 sample = 1Hz
Higher sample rate → Higher file size (more data stored) → Higher playback
quality
The length of an audio has no effect on playback quality, it only increases file size
- Sample interval: time in between samples
Decreasing sample rate means the sound will run faster, therefore sample rate
will increase
This is inversely proportional to sample frequency/rate
, - Bit depth: the number of different measurement values that can be stored (number of
bits used to store each sampled value) higher bit depth = more different values you can
measure
More bits → Higher accuracy to original sound → larger file size
- Higher sample rate + Higher bit depth → better approximation to original sound
The analogue sound from the speaker is sampled at a certain number of times per second. This
sampled data is then converted into discrete digital, binary data and stored on the computer
Higher sampling rate means higher number of analogue samples taken per second to be
converted into discrete digital data and stored. More analogue data stored means higher
playback quality as it would mean better approximation to original audio. More data stored
additionally means higher file size.
COMPRESSION
When large amounts of data are transmitted across the internet, it can be slow and expensive. If
data must be stored on a device with limited memory, it must be compressed to reduce
bandwidth and transmission times between devices and create space for more files to be
stored.
- Bandwidth: measure of data transfer rate or data capacity of a medium over a given
period of time
- Lossy compression: where some data is permanently removed to make the file smaller
Removed data is that least likely to be noticed by the human senses e.g. certain
frequencies of band sound inaudible to humans are discarded + large areas of similarly
coloured pixels are combined into one block of the same colour + video files where some
frames may be lost
The image still looks similar to the original
- For files like programs which only work with their full instructions or text which is only
legible with all characters present and in order, Lossless compression is more suitable
- Lossless compression: where a file is compressed without any original information being
lost
This involves storing enough data and information to be able to recreate the
original file exactly at decompression
The computer creates a dictionary of words used and a list providing their original
order
By referring to the dictionary, the original sequence can be reproduced
Storing the index and sequence requires a smaller file than storing the original
This way, files can be restored to their original condition without any data being
lost
SYSTEM ARCHITECTURE
A computer system is made up of hardware and software working together to process data
- The Central Processing Unit (CPU): made up of billions of transistors (small ‘on-off’
switches). It is the most important hardware in a computer and its main functions are
