OCR_Computing_GCSE_DataRepresentation Flashcards
Convert the denary number 106 into an 8 bit binary number.
01101010
Convert the denary number 106 into hexadecimal
6A
Peter takes a high resolution picture with a digital camera. The picture is stored in a bitmap file.
Describe how a picture is stored in a bitmap file.
The picture is split into a grid of pixels. Each pixel is given a binary code (which says what colour it is). The bitmap file contains the list of pixels along with meta data about the image e.g. height, width, colour depth, resolution etc.)
Peter wants to send the picture as an email attachment. State methods for reducing the size of the picture file so that it is suitable for sending as an email.
- Use image manipulation software to resize the image so that it uses less pixels.
- Reduce the colour depth to reduce the number of bits required to store each pixel.
3.Compress the file
Data stored in computers can be measured in bits, bytes and kilobytes.
State what is meant by a bit
A single binary digit, 0 or 1.
Data stored in computers can be measured in bits, bytes and kilobytes.
State what is meant by a byte
A group of 8 bits.
A file contains 5120 bytes. Calculate the size of the file in kilobytes. You must show your working.
5120 / 1024 = 5kB
An artist is recording sound using a computer. The graph below represents the pressure wave of the sound being recorded.
At point A on the graph, the size of the sound wave is 90. This is stored digitally using the binary value of 0101 1010 (or 5A in Hex).
What is the the size of the sound wave, the binary value and hex value at point C?
Size=60,
Binary=00111100,
Hex=3C
An artist is recording sound using a computer. The graph below represents the pressure wave of the sound being recorded.
At point A on the graph, the size of the sound wave is 90. This is stored digitally using the binary value of 0101 1010 (or 5A in Hex).
What is the the size of the sound wave, the binary value and hex value at point B?
Size=120,
Binary=01111000,
Hex=78
Explain how sampling intervals and compression can affect the size of a sound file and the quality of its playback. The quality of your written communication will be assessed in your answer to this question.
Sampling Rate
how close together the samples are taken the closer together, the more numbers need to be stored (and therefore larger file) but the sound that is created is closer to the original analogue mention of variable bit rates
Compression
use algorithms to make the file smaller (e.g for transmitting over Internet) and then recreated to be played can be lossy (eg mp3) and the recreated file is of poorer quality or lossless (eg flac) and the recreated file is exactly the same as it was before compression
Calculate the denary value of the 8-bit binary number 10010111. You must show your working.
128 64 32 16 8 4 2 1
1 0 0 1 0 1 1 1
128+16+4+2+1
151
Add the following two 8-bit binary numbers and explain the result. You must show your working.
1 0 0 1 0 1 1 1
1 1 0 1 1 0 0 0
An overflow has occurred because the result is more than 255 (cannot be represented in 8 bits).
Explain how ASCII is used to represent text in a computer system.
Each character is given a numeric code including symbols, digits, upper and lower case. This code is then stored in binary. Each character takes 1 byte. Text is stored as a series of bytes (1 per character). Some codes are reserved for control characters (eg TAB, Carriage Return)
State what is meant by the character set of a computer.
All the characters which are recognised/can be represented by the computer system.
Unicode is also used to represent text in a computer system. Explain the difference between the character sets of Unicode and ASCII.
Unicode has a much larger character set, representing symbols from many different alphabets. This is possible because each character uses 16 bits whereas ASCII only uses 8 bits.
