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Flashcards Edexcel GCSE Computer Science

2.3 Data storage and compression

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What is meant by a byte?
A group of eight bits, which can store one character of text
Which term describes a single binary digit, which is either a 0 or a 1?
Bit
What is meant by a kibibyte?
A unit of data storage equal to 1024 bytes
Which term describes a unit of storage that is equal to 1024 kibibytes?
Mebibyte
What is meant by a tebibyte?
A unit of data storage equal to 1024 gibibytes
What is meant by a gibibyte?
A unit of data storage equal to 1024 mebibytes
How many nibbles are there in one byte?
2
How many bits are there in one nibble?
4 bits
A sound file has a size of 3 MiB. What is its size in KiB?
3072 KiB
Which list shows units in order from smallest to largest?
Bit, nibble, byte, kibibyte, mebibyte
Which statement explains why one kibibyte is 1024 bytes rather than 1000 bytes?
1024 is a power of 2
A memory card holds 16 GiB of data. Each photograph takes 4 MiB. How many photographs can it hold?
4096
Which of these is the largest amount of storage?
3 GiB
Which of these is a sensible file size for a small digital colour photograph?
3 MiB
Which term describes the process of restoring compressed data to its original format?
Decompression
Which term describes a method of reducing file size that permanently removes some data, which can reduce the quality of an image or sound?
Lossy compression
What is meant by 'lossless compression'?
A method of reducing file size that keeps all of the original data so the file can be restored exactly
What is meant by a 'digital artefact' in a compressed image or video?
A small mistake, such as a block or a patch of noise, that appears after some data has been permanently removed
What is meant by 'dictionary compression'?
A lossless method that finds repeated patterns of data and stores each pattern once alongside a code
What does compression mean when it is applied to a computer file?
Reducing the size of a file using an algorithm
A file is compressed using a lossy algorithm. What happens to the data that is removed?
It is lost permanently and cannot be recovered
A company wants to make a program file smaller so it can be downloaded more quickly. Why must lossless compression be used?
Every instruction must be restored exactly as it was
A photograph is compressed with a lossy algorithm and then enlarged on screen. What is likely to be visible?
Blocks and noise where colours contrast
Why does a compressed file download faster than the uncompressed version of the same file?
Fewer packets of data need to be transferred
An MP3 music file is much smaller than the same track stored without compression. Why is this?
Sounds that listeners are unlikely to notice are not stored
Why is compression useful when a file is being sent as an email attachment?
The file is more likely to stay within the size limit
Which of these file formats uses lossy compression?
MP3
A company compresses its files before copying them onto a backup drive. What is the main benefit of compressing the files first?
More data can be stored using the same amount of space
The same sound file is compressed twice, once with a lossy algorithm and once with a lossless algorithm. How do the two compressed files compare?
The lossless file is larger but can be restored exactly
A single uncompressed frame of high definition video needs around 50 megabits of data. Why does this make compression necessary?
The video would need far too much data to store or send
A video keeps stopping and showing a buffering message while it is being streamed. What is the most likely reason?
The data is arriving more slowly than the video is being played