Text, Sound & Images

• Character sets (ASCII & UNICODE) give every character on your keyboard a unique binary code.
• ASCII uses 7 bits (128 characters) — good enough for English, useless for most other languages.
• Extended ASCII uses 8 bits (256 characters) — adds a few extra symbols.
• UNICODE uses a minimum of 16 bits (65,536+ characters) — covers every language and emoji on Earth.
• Sound is analogue in real life, but computers need it digital — this conversion is called Analogue to Digital conversion (A2D).
• Sample rate (Hz) = how often the sound wave is measured per second.
• Sample resolution (bits) = how much detail is stored per measurement.
• Bitmap images are grids of pixels, each pixel holding a binary colour code.
• Resolution = total number of pixels (width × height). Colour depth = bits per pixel.
• Across the whole chapter, one rule keeps repeating: more detail = more bits = bigger file.

Deep down, a computer has no idea what a "letter" is. All it can store is binary — strings of 1s and 0s. So if you want to store the letter A, everyone (every keyboard, every screen, every app) needs to on which binary pattern means "A". That agreed-upon list of characters and their binary codes is called a character set.

Think of it like Morse code. Dot-dot-dot only means "S" because everyone using Morse code agreed on that mapping beforehand. If your computer used one mapping and mine used a different one, the moment you sent me a text file it would come out as gibberish — that's exactly the problem the chapter's PDF points out: without a shared standard.

Character sets are also ordered logically — the code for 'B' is exactly one more than the code for 'A', 'C' is one more than 'B', and so on. This is genuinely useful: it means a computer can sort text alphabetically just by comparing the binary numbers, and it can figure out that lowercase and uppercase letters are related by a simple fixed offset.

The number of characters a set can represent depends entirely on how many bits it uses per character. This is just the maths of binary: with bits you can make 2ⁿ different patterns, so 2ⁿ different characters.

ASCII (American Standard Code for Information Interchange) was one of the earliest accepted standards for representing text. It uses 7 bits per character, which gives:

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