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Explain why data must be stored in a binary format. [2]
Computers make use of logic gates / electric switches [1] which are either on or off, represented in binary as a 1 or 0 [1]
State the mnemonic to remember the order of units of data...
Burger King Makes Great Toast (P)
Calculation for... sound file size =
sample rate x duration (s) x bit depth
Calculation for... image file size =
colour depth x image height (px) x image width (px)
Calculation for...text file size =
bits per character x number of characters
Explain the effect of performing a two-place shift to the left of the binary number 00110010.[1]
It multiplies the number by 4.
Explain the effect of performing a right shift of the binary number 10011011. [2]
The number will be halved.[1] There will be a loss of precision[1]
What is an overflow error? [2]
Overflow occurs when the result of adding two binary numbers [1] is greater than the number of bits the CPU is expecting[1] - this extra bit is stored elsewhere.[1]
What do left and right shifts cause? [2]
- left shifts cause overflow - right shifts cause loss of accuracy/ data
Give two reasons why colour codes are given in hexadecimal rather than binary. [2]
Easier to read / remember than binary (1) Less chance of input error (1) as two digits represent 8 bits (1).Easier to convert between binary and hex than binary and denary (1)
ASCII is one type of character set. (a) Define the term character set. [1]
Character sets are collections of characters that a computer recognises from their binary representation.
ASCII makes use of 8 bits to represent each character. Explain how 256 different characters can be stored in the character set. [2]
The range of binary numbers is from 00000000 to 11111111 [1] 11111111 represents the number 255 in denary. Including 0, there are therefore 256 different characters that can be represented [1]
Compare ASCII to extended ASCII? [2]
- Extended ASCII uses more bits than ASCII - Extended ASCII can represent more characters than ASCII - ... for example Extended ASCII can represent other languages/ symbols
Explain one limitation of ASCII.
ASCII only uses 7 bits (or 8 for extended ASCII) So it can only represent 128 (or 256) characters. This is not enough to represent characters in other alphabets, e.g. Russian, Arabic, etc.
What is meant by Unicode? [2]
Unicode uses 16-bits per character [1] and covers all major languages [1]
Unicode is also used to represent text in a computer system. Explain the difference between the character sets of Unicode and ASCII. [2]
Unicode has a much larger character set, representing symbols from many different alphabets.[2] This is possible because each character uses 16 bits whereas ASCII only uses 8 bits.[2]
What is meant by a Pixel? [1]
Smallest element that makes up an image (a tiny dot)
How is a bitmap image stored? [3]
- made up of pixels - each have a unique binary code - code for colour - binary number stored in order
Define the meaning of resolution. [1]
The concentration of pixels within a specific area (1).
Metadata often accompanies image data. Give two examples of metadata. [2]
height[1] width[1] bit depth[1] resolution[1], date created[1]
How does the resolution affect the size of the bitmap file? [2]
The higher the resolution [1] the more pixels that are required for the picture which will increase the size of the bitmap file [1]
Explain the effect of using a higher colour depth than 3 bits for the image. [2]
The quality of the image will be improved. [1] This is because more bits are available per pixel to represent a greater range of possible colours. [1]
A grayscale image has four shades of grey. (a) Explain the colour depth required to store this image. [2]
Four shades of grey will be stored with a bit-depth of 2 bits[1]. The bit patterns needed for four shades of grey are 00, 01, 10, 11 - so just two bits are required[1]
When recording a sound file on a computer, the sound needs to be sampled. Describe how sampling is used when storing sound. [2]
- The height / amplitude of the sound wave is measured ... - at regular intervals ... - and converted to binary.
Explain the effect of the sampling interval on the size and quality of the sound file recorded. [3]
- If the interval is smaller / if you sample more often you have more data to store - ... so larger file - but the sound reproduced is closer to the original... - ...so better quality
What is meant by a duration? [1]
how many seconds of audio the sound file contains [1]
How is sound sampled and stored in digital form? [3]
- Sound is recorded by a microphone as an analogue signal (continually changing) - This analogue wave is converted into digital data (by an analogue to digital converter) - This process is called sampling
What is the difference between analogue sound waves and digital data? [2]
- An analogue sound wave is one continuous piece of data which keeps changing - Digital data is not continuous and it's lost a lot of data.
Explain the effect of the bit depth on the size and quality of the sound recording. [3]
- higher bit depth means more accurate/ better quality - as quieter sounds are picked up but... - higher means larger file size
Files are often compressed before they are sent over the internet. State what is meant by compression. [1]
Reduce the size of the file. [1] Transmits more quickly / uses less bandwidth [1]
Compression is often used to reduce the size of files before sending them electronically. What is one advantage for compressing files in this way?
Reduce download size. Reduce download time when transferring a file. Reduce storage requirement.
Explain the two types of compression most commonly used? [4]
With lossy compression some of the original data is lost. (1) This (often) allows for a greater level of compression (1). The data that is lost will typically not be noticeable (1).With lossless compression the compressed file has exactly the same data as the original (1), with a reduced file size (1). No loss in data means no loss in quality (1)
What are the types of compression and what files are they? [4]
Lossy: JPEG, GIF, MP3 Lossless: PNG, TIFF
Kofi uses his computer to record an audio file of himself playing his guitar. He emails his recording to a record label. He uses lossy compression to produce the music file. Explain two reasons why using lossy compression is beneficial.[2]
- Lossy means the decompressed file is not identical to the original... - ...the difference is unlikely to be noticed by humans - Lossy will decrease the file size ... - ... so it can be sent via e-mail
The website of a school allows visitors to download JPG, MP3, MPEG and PDF files. The video clip is compressed using lossy compression. Explain why lossy compression is suitable for a video clip, but not suitable for a text document. [3]
- When the file is compressed some detail / data / quality / resolution is lost... - ... which is not noticeable in the video file / video still viewable with lower quality - ... but would make the text file unreadable / lose meaning or comprehension
A large software program is being distributed via an online download. Explain which type of compression should be used to compress the software. [2]
- Lossless compression[1] - software must be used as no data in the software program can be lost[1]. - Lost data would prevent the software from running once uncompressed[1].
Lossy compression is used to compress the band's song. Explain one advantage and one disadvantage of using lossy compression [4]
Advantage A significant reduction in the size of the file can be made. This will result in less time to download the song. Disadvantage Some of the original data of the recorded song will be lost. This will result in a reduction in the quality of the music .
Ray needs to make sure his recording can be sent by email. Suggest a suitable file format for the file and explain why this is a suitable format. [2]
MP3 format. (1) It is compressed, (1) will become a much smaller file, will therefore take up less bandwidth (1) on his connection and take less time to transmit. (1) Also some email recipients will be unable to receive large files (1)
State which type of compression is most appropriate for each of the following and explain why it is appropriate.Downloading the source code of a large program... [2]
- Lossless compression - The code has to be exactly as it was originally written - ... or else it will not work.
State which type of compression is most appropriate for each of the following and explain why it is appropriate. Streaming a large video file... [2]
- Lossy compression - Achieves higher compression / smaller file size / faster streaming than lossless - Video can still be viewed at lower quality (from the data compressed).
