Computer Science - 4CP0 PearsonEdexcel

Data Representation

Muhtasari

A photograph, a song and a paragraph of text look nothing alike, yet a computer stores all three the same way: as binary digits. The difference is entirely in how those digits are agreed to be interpreted, letter by letter for text, pixel by pixel for an image, sample by sample for sound.

In this lesson you will learn how characters are encoded using ASCII and Unicode, how a bitmap image's resolution and colour depth determine its uncompressed file size, how an analogue sound wave is converted into binary using sampling, and why the number of bits available always limits how faithful any of these digital representations can be.

Malengo

  1. Understand how computers encode characters using ASCII and Unicode
  2. Understand how bitmap images are represented in binary (pixels, resolution, colour depth)
  3. Understand how sound, an analogue signal, is represented in binary
  4. Understand the limitations of binary representation of data (sampling frequency, resolution) when constructed by the number of available bits

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Maelezo ya Somo

A computer has no built-in idea of what a letter is. To store text, every character a keyboard can produce is given its own unique binary number, called a character code. ASCII (American Standard Code for Information Interchange) does this using 7 bits, giving 128 possible codes, enough for the upper- and lower-case English alphabet, digits, punctuation and basic control characters. An 8-bit version, extended ASCII, adds a further 128 codes for accented letters and symbols.

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Tathmini ya Somo

Hongera kwa kukamilisha somo la Data Representation. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.

Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.

Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.

  1. The upper-case letter 'A' has the ASCII code 65. What is the ASCII code of the lower-case letter 'a'? A) 33 B) 66 C) 97 D) 129 Answer: C
  2. An image is 100 pixels wide, 50 pixels tall, and uses a colour depth of 8 bits. What is its uncompressed file size in bits? A) 4 000 B) 8 000 C) 40 000 D) 400 000 Answer: C
  3. Which setting controls how many amplitude levels a single digital audio sample can be stored as? A) Sample rate B) Bit depth C) Number of channels D) File format Answer: B
  4. A recording is made with too low a sample rate. What is the most likely effect on the digital recording? A) The file becomes larger than expected B) Rapid changes in the original sound are missed C) The recording gains extra colour depth D) The recording becomes louder Answer: B
  5. What is the main reason Unicode was developed alongside ASCII? A) To make text files smaller B) To represent far more characters than ASCII can, covering the world's writing systems and symbols C) To replace binary with a new number system D) To increase a computer's sample rate Answer: B

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Vitabu Vinavyopendekezwa

Pearson Edexcel International GCSE (9-1) Computer Science Student Book
Pearson Edexcel International GCSE (9-1) Computer Science Student Book
Manukuu: First edition
Mchapishaji: Pearson Education
Mwaka: 2019
ISBN: 978-0-435-19124-9
Maelezo: Endorsed student book covering the full 4CP0 specification with programming tasks and exam practice.

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