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Flashcards · 9210 · Topic 3

Data representation flashcards

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Topic 3: Data representation

Why do computers use binary?
Their circuits are made of switches (transistors) with two states, on and off, which represent 1 and 0.
How do you convert binary 1011 0110 to hexadecimal?
Split into groups of four bits: 1011 = B and 0110 = 6, so B6.
Why is hexadecimal used?
It is a shorter way of writing binary that is easier for people to read and less error-prone; each hex digit stands for four bits.
What are the units of storage from bit to gigabyte?
A bit (b) is a 0 or 1; a byte (B) is 8 bits. 9210 uses decimal prefixes: 1 kB = 1,000 bytes, 1 MB = 1,000 kB, 1 GB = 1,000 MB, 1 TB = 1,000 GB.
What does a binary shift do?
A left shift by one place multiplies a number by 2; a right shift by one place divides it by 2 (any remainder is lost).
What is a character set? Compare ASCII and Unicode.
A set of characters with a binary code for each. 7-bit ASCII has 128 codes (English). Unicode represents many alphabets and special symbols, a far greater range, and uses the same codes as ASCII up to 127.
How do you calculate the file size of a bitmap image?
Width in pixels × height in pixels × colour depth (bits per pixel) gives the size in bits; divide by 8 for bytes.
How do you calculate the file size of a sound recording?
Sample rate (Hz) × sample resolution (bits) × duration (seconds) gives the size in bits.
How do you build a Huffman tree?
Count the frequency of each character, then repeatedly join the two items with the lowest totals into a new node holding their sum until one root remains. Label branches 0 and 1; a code is the path from the root.
How do you calculate the bits needed for Huffman-compressed data?
Add up frequency × code length for every character. Compare with uncompressed 7-bit ASCII: number of characters × 7.
Why do frequent characters get short Huffman codes?
They are joined last, so they sit near the root and need fewer branches (bits), which minimises the total size.
Write 0000011100000011 in run length encoding
5 0 3 1 6 0 2 1. Each pair is a frequency then the data value (the specification's own example).
What range of values must you convert between bases in 9210?
Decimal 0 to 255, which is binary 0000 0000 to 1111 1111 and hexadecimal 00 to FF.

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