Data Storage & Compression (Cambridge (CIE) O Level Computer Science)
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What is a bit?
A bit is the smallest unit of data storage, representing a single binary digit
(either 1 or 0.)How many bits are in a byte?
A byte is 8 bits.
How many bits are in a Kibibyte?
A kibibyte is 1024 bytes (2^10 bytes).
What is the difference between a megabyte and a mebibyte?
A megabyte is
bytes, while a mebibyte is 
bytes.True or False?
When converting between units larger than a byte, we use multiples of 1000.
False.
When converting between units larger than a byte, we use multiples of 1024 (2^10).
How do you convert from bytes to bits?
To convert from bytes to bits, multiply by 8.
What is a Tebibyte?
A tebibyte is 1,099,511,626,776 bytes (2^40 bytes).
What is the symbol for mebibyte?
The symbol for mebibyte is MiB.
True or False?
A nibble is 2 bits.
False.
A nibble is 4 bits.
How do you convert from kibibytes to bytes?
To convert from kibibytes to bytes, multiply by 1024.
What is the formula for calculating the size of a bitmap image?
The size of a bitmap image is calculated by:
Resolution x colour depth
or
Image width x image height x colour depthDefine resolution.
Resolution is the total number of pixels in an image, calculated by multiplying the image width by the image height.
Define colour depth.
Colour depth is the number of bits used to represent the colour of each pixel.
True or False?
A colour depth of 24 bits is equal to 3 bytes.
True.
A colour depth of 24 bits is equal to 3 bytes.
What is the formula for calculating the size of a sound file?
The size of a sound file is calculated by
Sample rate x duration x sample resolution.
Define sample rate.
Sample rate is the number of samples taken per second in a digital audio recording.
Define sample resolution.
Sample resolution is the number of bits stored per sample in a digital audio recording.
How do you convert file size from bits to bytes?
To convert file size from bits to bytes, divide by 8.
How do you convert file size from bytes to kibibytes?
To convert file size from bytes to kibibytes, divide by 1024.
True or False?
The resolution of an image is measured in bits.
False.
The resolution of an image is measured in pixels (width x height).
Define compression.
Compression is reducing the size of a file so that it takes up less space on secondary storage.
State three benefits of compression.
Three benefits of compression are:
Less storage space required
Less bandwidth required
Shorter transmission time
Define lossy compression.
Lossy compression is a method of data compression where data is lost in order to reduce file size, resulting in a loss of quality but smaller file sizes.
Define lossless compression.
Lossless compression is a method of data compression where data is encoded to reduce file size without losing any information, allowing the original data to be perfectly reconstructed.
True or False?
Lossy compression is reversible.
False.
Lossy compression is irreversible.
What types of files are suitable for lossy compression?
Files suitable for lossy compression are those where reducing quality is acceptable, such as images, video, and sound files.
How does lossy compression work on photographs?
In photographs, lossy compression tries to group similar colours together, reducing the number of colours in the image without significantly compromising the overall visual quality.
True or False?
Lossless compression can be used on all types of data.
True.
Lossless compression can be used on all types of data.
How does lossless compression work on documents?
In documents, lossless compression uses algorithms to analyse the contents, looking for patterns and repetition, such as replacing repeating characters with a single character and the number of occurrences.
What is an advantage of lossless compression over lossy compression?
An advantage of lossless compression is that the file can be returned to its original state without any loss of data quality.