What it covers: How the Internet moves data, how networks stay reliable through fault tolerance, and how parallel and distributed computing speed up large tasks.
Exam weight: Big Idea 4 is about 11–15% of the AP CSP multiple-choice exam.
The big question: How do computers communicate over networks reliably, and how does dividing work make computing faster?
Computational thinking practices: Computational Solution Design, Algorithms & Program Development, Abstraction, Code Analysis, Computing Innovations, and Responsible Computing.
Key topics at a glance
The Internet
A network of networks. Every device has an IP address; data is split into packets that route independently and reassemble at the destination.
Protocols
Agreed rules for communication. TCP/IP (addressing + reliable delivery), HTTP (web pages), DNS (domain names → IP addresses).
Packets & Routing
Packet switching: messages become packets that may take different routes. Routers forward packets toward the destination address.
Bandwidth & Latency
Bandwidth = data per unit time a connection can carry. Latency = the delay for data to travel from source to destination.
Fault Tolerance
A system's ability to keep working when parts fail. The Internet is fault tolerant because of redundancy.
Redundancy
Duplicate components and multiple paths. If one route or router fails, data reaches its destination another way.
Parallel Computing
A task is split into parts that run at the same time on multiple processors, finishing faster than sequential computing.
Distributed Computing & Speedup
Multiple networked computers share one problem. Speedup = sequential time ÷ parallel time; limited by the sequential portion and overhead.
The key terms you must know
Internet — a global network of networks connecting devices.
IP address — a unique numeric address identifying a device on a network.
Protocol — agreed rules for formatting, sending, and receiving data.
TCP/IP — core Internet protocols for addressing/routing and reliable delivery.
HTTP / DNS — the web-page protocol; the domain-name-to-IP-address system.
Packet — a chunk of data with routing/address information.
Packet switching — sending packets independently, reassembled at the destination.
Router — a device that forwards packets between networks.
Bandwidth — data transfer capacity per unit time.
Latency — the delay for data to travel across a network.
Fault tolerance — the ability to keep working when parts fail.
Redundancy — duplicate components/paths that enable fault tolerance.
Parallel computing — running parts of a task at once on multiple processors.
Distributed computing — many networked computers solving one problem.
Speedup — how many times faster a parallel solution runs.
Key themes to remember
The Internet is open and layered. Shared protocols let very different devices communicate.
Packets travel independently. Splitting messages makes transmission flexible and resilient.
Redundancy creates fault tolerance. Multiple paths keep the network working when parts fail.
Parallelism trades hardware for speed. Splitting work across processors or computers finishes big tasks faster.
Speedup has limits. Sequential portions and coordination overhead cap how much faster parallel gets.
Common exam traps
The Internet is not the same as the World Wide Web. The Web (HTTP pages) runs on top of the Internet; the Internet is the underlying network.
Packets can take different routes and arrive out of order; TCP reassembles them correctly.
Redundancy is the reason for fault tolerance, not extra speed — its purpose is reliability.
Parallel ≠ distributed. Parallel uses multiple processors; distributed uses multiple separate computers over a network.
More processors don't give unlimited speedup. The sequential part of a task and overhead limit it.
Bandwidth is capacity; latency is delay. High bandwidth does not guarantee low latency.
An IP address identifies a device, while a protocol defines the rules of communication — different ideas.