AP Computer Science Principles is a breadth-first introduction to computer science — it covers programming, data, internet, algorithms, and the social impacts of computing without requiring mastery of any single programming language. The exam includes a Create Performance Task (submitted before the exam) and an end-of-year exam. Here's how each part works.
The Five Big Ideas
All AP CSP content organizes around five big ideas: (1) Creative Development — iterative software design, collaboration, documentation; (2) Data — binary representation, data compression (lossless vs. lossy), extracting information from data, privacy concerns; (3) Algorithms and Programming — sequencing/selection/iteration, boolean logic, lists, procedures, parameters, return values, nested conditionals; (4) Computing Systems and Networks — hardware abstraction, the internet protocol stack, packet switching, fault tolerance, scalability; (5) Impact of Computing — digital divide, intellectual property, cybersecurity, surveillance, computing bias, and beneficial vs. harmful effects.
Big Idea 2: Data — What to Know
Binary: understand base-2 representation, bit vs. byte, and how binary encodes integers, colors (RGB), and text (ASCII/Unicode). Know that compression reduces file size — lossless compression (ZIP) reconstructs the original perfectly; lossy compression (JPEG, MP3) permanently removes data. Data analysis: understand how metadata, sample size, and data collection methods can introduce bias. Privacy: data is often collected beyond what users realize — cookies, location services, transaction logs. Know the concept of personally identifiable information (PII) and the tradeoffs of sharing data.
Big Idea 3: Algorithms and Programming
Sequential, conditional (if/else), and iterative (loop) program structures — know how to trace through pseudocode. Procedures (functions) with parameters allow code reuse. Lists (arrays) allow storing multiple values — accessing by index, iterating through a list. Understand what makes an algorithm correct (does it produce the right output for all inputs?) and efficient (does it scale well as input size grows?). The undecidability problem: some problems cannot be solved by any algorithm — the Halting Problem is the canonical example.
Big Idea 4: The Internet
The internet uses packet switching — data is broken into packets, sent independently, and reassembled. IP addresses identify devices; DNS translates domain names to IP addresses. The TCP/IP protocol stack handles reliability (TCP) and routing (IP). HTTP/HTTPS transfers web content — HTTPS uses TLS for encryption. Cybersecurity: understand symmetric vs. asymmetric encryption (public key/private key), phishing, malware, DDoS attacks, and the role of authentication and authorization.
Create Performance Task
The Create PT is a programming project you build before the exam. You must: write a program that uses a list and a procedure with a parameter and return value, then submit a video of your program running, a PDF of your code, and written responses explaining your program's purpose, the algorithm you implemented, and how the list and procedure work. College Board scores it with a rubric — each component earns 0–1 points. The most commonly missed points are: (1) not demonstrating a meaningful list operation, (2) procedure doesn't include a parameter, (3) written response doesn't describe the algorithm in enough detail.
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