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Unit 4 · Computer Systems & Networks Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Computer Science Principles Unit 4 Visual Review

A topic-by-topic visual walkthrough of Big Idea 4: Computer Systems and Networks — the Internet, fault tolerance, and parallel and distributed computing.

← Back to Unit 4 hub
TOPIC 4.1 The Internet DATA TRAVELS IN PACKETS A B packets take independent routes A → B Packets & protocols Data is split into PACKETS that travel independently and are reassembled. PROTOCOLS are agreed rules: IP addresses, TCP (reliable delivery), HTTP (web), DNS. The Internet is a network OF networks. Scalable & redundant by design Redundant paths mean if one route fails, packets reroute. Open protocols let the network grow (scale) to any size. The Internet routes packets using shared protocols — redundant and scalable. The Review Hub · AP Computer Science Principles · Big Idea 4 TOPIC 4.2 Fault Tolerance Keep working when parts fail A FAULT-TOLERANT system keeps operating even when a component fails. The Internet achieves this with REDUNDANCY — multiple paths between any two points. Redundant routing If one connection or router goes down, packets automatically take another route. More paths = more fault tolerance, but also more cost to build and maintain. Backups and duplicated data also add tolerance. A single point of failure is the enemy If one part's failure stops the whole system, it is NOT fault tolerant. Redundancy removes single points of failure. Redundancy makes a system fault tolerant — it keeps working when a part fails. The Review Hub · AP Computer Science Principles · Big Idea 4 TOPIC 4.3 Parallel & Distributed Computing Parallel computing Breaks a task into parts that run at the SAME TIME on multiple processors. SPEEDUP = sequential time ÷ parallel time. Some steps must stay sequential, so speedup is limited — never perfectly ×N. Distributed computing Uses MANY separate computers working together over a network on one problem. Lets you tackle problems too big for a single machine (huge data, science). Solutions scale by adding more computers. Speedup example A job takes 60s sequentially and 20s in parallel → speedup = 60 / 20 = 3×. The sequential portion caps the gain. Parallel runs parts at once (speedup = seq ÷ parallel); distributed spreads work across computers. The Review Hub · AP Computer Science Principles · Big Idea 4
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I explain how a packet travels, or why the Internet is fault tolerant, from memory?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This is great for review the night before the exam — fast, visual, and covers every idea you need to recognize in Unit 4.