1.2 Flashcards
State characteristics of secondary storage devices that Nina should consider when choosing a device
Capacity
Speed
Portability
Durability
Reliability
Cost
What is meant by the capacity of a storage device
Refers to how much data needs to be stored
What is meant by the speed of a storage device
Speed: refers to how quickly can data be read and transferred?
What is meant by the portability of a storage device
Portability: refers to if data needs to be transported, are size, shape and weight important?
What is meant by the durability of the storage device
Refers to how robust the media is
Will it be damaged by shocks, and extreme conditions?
What is meant by the reliability of the storage decice
does it need to be used over and over again without failing?
What is meant by the cost of the storage device
how expensive is the media per byte of storage?
why data needs to be converted into binary to be processed by a computer
With just two states, electronic components are:
Easier to manufacture
Therefore cheaper
More reliable
Examples of using two states to store data:
ram
hard disk
optical disk
flash memory
effect of binary left shift
multiply binary number by 2
effect of binary right shift
divide binary number by 2
remember to circle overflows in the exam and label it - overflow
a character set is
A defined list of characters recognised by the computer hardware and software. With each character being represented by a single number
examples of character set
Ascii - 7 bit character set
Extended ascii - 8 bit character set
Unicode
How are images represented
Each pixel has a specific colour, represented by a specific code
Bitmap pictures are constructed from coloured squares called pixels
an image is represented as a series of pixels, represented in
binary
Each pixel of a bitmap is stored in binary
How many colours can 1 bit store
How many colours can 2 bit score
The number of bits required for each pixel depends on the number of colours required
1 bit has 2 possible values: 0 and 1. Therefore 1 bit can store 2 colours: black or white
2 bits have 4 possible values: 00, 01, 10 and 11. Therefore 2 bits can store 4 colours.
How can the number of colours be calculated
The number of colours can be calculated as 2n. Where ānā is the number of bits for each pixel
What is colour depth
The number of bits for each pixel is known as the colour depth
What is metadata
Metadata is additional data stored with the image to define the width, height, colour depth and colour palette.
How to make image quality better
The greater the colour depth and resolution, the larger the file size of the image (and quality of the image)
What is resolution
Resolution is the number of pixels in a bitmap image
Photographs are stored in 24 bit colour depth
Calculate no. of colours
. Each pixel is stored in 24 bits. This is 2^24 = over 16 million colours
The number of different colours the human eye can see.
What affects the quality of a digitally converted sound wave and the file size?
Sample rate (speed)
Bit Depth (detail)
what is sample rate
Sample rate:
The number of samples stored per second
the sample rate is the number of times per second the amplitude of the sound wave is measured - measured in khZ
e.g. cd quality is 44.1khz (44,100 samples per second)
higher sample rate means
The higher the number of samples per second, the higher the quality of the sound (the better the audio quality as the digital data more closely resembles an analogue wave), and the larger the file size
what is bit depth
Bit depth:
The number of bits stored per sample
the number of bits available to represent each sample
e.g. a sample with a bit depth of 4 could be 0101 or 0111 or 1010
A sample with bit depth of 8 could be 01100110
common bit depth is
higher bit depth means
The higher the number of bits, the greater the quality of the sound, and the larger the file size
higher bit depth, the more bits are available to be used for each sample. Therefore the quality is often higher as teh wave more closely resembles an analogue wav
file size will be larger, - if the bit depth is higher, as each sample stores additional bits
how to calculate file size for sound
The total number of bits in a sound
Calculated as the (Number of samples per second) x (Number of bits per sample) x (Length of sample in seconds)
sample rate (In hertz) x bit depth x duration (in seconds)
problem with digital sound wave
digital saplining is discrete (separate) and not continuous like analogue waves
Its lost a lot of data
in sound, how can the digital data be improved
how to get highest quality sound
The digital data can be improved by taking samples more regularly
to get the highest quality sound, many samples are taken to recreate the analouge wave as closely as possible
what will a low sample rate result in
A low sample rate will result in a low-quality sound because the digital data dos not closely resemble the original analogue wave
reasons for compression
Compression reduces the size of a file so it takes up less space.
Maximise the amount you can store on a device.
Smaller files are quicker when transferred (streamed) over the internet.
files take up less storage space (so more files can be stored)
files can be transferred quicker because they are smaller
files can be read from or written to quicker
what increases the file sizes of images
number of colours - because we need more bits per pixel to store a greater range of possible colours
one way to make image file size smaller
One way to make the file size smaller would be to store a lower number of colours
Or to store bigger areas of pixels as one colour
Both of these techniques will reduce the quality of the image
This is known as lossy compression
types of compression
lossy
lossless
features of lossy compression
Some of the data is lost and cannot be recovered
Greatly reduces the file size
Reduces the quality of the image/sound
Suitable for images, sound and video
Cannot be used on text and executable files
FEATURES OF LOSSLESS COMPRESSION
None of the data is lost, it is encoded differently
Can be turned back into original format
Can be used on all types of data
Is usually less effective than lossy compression at reducing the file size
Most suitable for documents and executable files.
equation for file size for text files - characters
file size = number of bits per character xnumber of characters
file size in bits
file size for images equation
file size = image resolution x colour depth = width x height x colour depth
colour depth also known as bit depth
1 bit represents 2 colours ( black and white)
