Flashcards · 9618 · AS Topic 1

Information representation (AS Level) flashcards

16 cards on AS Topic 1, subtopics 1.1 to 1.3. Pick a subtopic or study them all.

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How do you convert a denary number to binary?: Repeatedly divide by 2 and read the remainders upwards; or subtract the largest place values (128, 64, 32 …) that fit and write a 1 in each one used.
Why is hexadecimal used in computing?: It is far more compact than binary and each hex digit maps to exactly four bits, so conversion is easy and errors are less likely. Used for memory addresses, colour codes and MAC addresses.
How do you find the two’s complement of a binary number (to negate it)?: Invert all the bits and add 1. Example: +5 = 00000101 → 11111010 → 11111011 = −5.
What is the range of an 8-bit two’s complement integer?: −128 to +127. In general, n bits give −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1.
What is binary-coded decimal (BCD)?: Each denary digit is stored separately as its own 4-bit binary code. 59 in BCD is 0101 1001. Used where digits are displayed or exact decimal values matter, such as in calculators and electronic displays.
What is the difference between a kibibyte and a kilobyte?: A kibibyte (KiB) is 2¹⁰ = 1024 bytes (binary prefix). A kilobyte (kB) is 10³ = 1000 bytes (decimal prefix). Likewise MiB = 2²⁰ bytes and MB = 10⁶ bytes.
ASCII and Unicode: how many bits, and why was Unicode needed?: ASCII uses 7 bits (128 characters); extended ASCII uses 8 bits (256). Unicode uses up to 32 bits per character, so it can represent non-Latin scripts and symbols that ASCII cannot.

What is image resolution, and what is colour depth?: Resolution: the number of pixels in the image (width × height). Colour depth: the number of bits per pixel; n bits give 2ⁿ colours.
How do you estimate the file size of a bitmap image?: File size (bits) = width in pixels × height in pixels × colour depth. Divide by 8 for bytes.
What is the difference between a bitmap and a vector graphic?: A bitmap stores the colour of every pixel. A vector graphic stores a drawing list of objects and their properties (e.g. coordinates, line colour, fill), so it scales without loss of quality but is unsuitable for photographs.
What are sampling rate and sampling resolution in digital sound?: Sampling rate: the number of samples taken per second (Hz). Sampling resolution: the number of bits used to store each sample.
How do sampling rate and resolution affect a sound file?: Increasing either gives a more accurate representation of the original sound, but a larger file. File size = sampling rate × sampling resolution × duration (× number of channels).

What is the difference between lossy and lossless compression?: Lossless: the original data can be fully recovered (used for text and program files). Lossy: some data is permanently discarded, usually detail people barely notice (used for photos, audio and video).
Why is file compression needed?: Smaller files use less storage space and transfer faster over a network, using less bandwidth.
How does run-length encoding (RLE) work?: A run of identical values is replaced by one copy of the value and a count. Example: AAAAABB → 5A2B.
When is run-length encoding a poor choice?: On noisy or photographic data with few repeated runs: the encoded file can end up larger than the original.