Everything a computer stores is data — and data is just bits. This big idea covers how numbers are represented in binary, how data is compressed to save space, and how programs turn raw data into useful information.
Six ways to master Unit 2 — pick whichever fits how you like to study.
All 4 topics from the College Board CED, in order.
Unit 2 covers Big Idea 2: Data. At the lowest level, all data in a computer is stored as bits — 0s and 1s. You'll learn how numbers are represented in binary, how to convert between binary and decimal, and the key fact that n bits can represent 2ⁿ different values. Because bits are an abstraction, the same sequence of bits can represent numbers, text, images, or sound depending on how it is interpreted.
The unit then covers data compression — shrinking data to save storage and transmission time. Lossless compression reduces size with no information lost (the original is fully recoverable), while lossy compression discards some data for a smaller size, trading fidelity for space. Finally, you'll study how programs extract information from data — finding patterns, using metadata, cleaning data, and remembering that correlation does not imply causation — and how programs process datasets far too large for people to handle by hand.
This is Big Idea 2, worth 17–22% of the multiple-choice exam. The six computational thinking practices below spiral through this and every big idea: