Unit 4 · Computer Systems and Networks

Computing device ● (core concept) — A physical artifact that can run a program. Examples include computers, tablets, servers, routers, and smart sensors.

Computing system ● (core concept) — A group of computing devices and programs working together for a common purpose.

Computer network ● (core concept) — A group of interconnected computing devices capable of sending or receiving data. A computer network is itself a type of computing system.

Path ● (core concept) — A sequence of directly connected computing devices on a network that begins at the sender and ends at the receiver.

Routing ● (core concept) — The process of finding a path from a sender to a receiver on a network. Routing on the Internet is usually dynamic; it is not specified in advance.

Bandwidth ● (core concept) — The maximum amount of data that can be sent over a network in a fixed amount of time, usually measured in bits per second.

Internet ● (core concept) — A computer network made of interconnected networks that use standardized, open (nonproprietary) communication protocols. Because the protocols are open, new devices connect easily, and the Internet was designed to be scalable.

Protocol ● (core concept) — An agreed-upon set of rules that specifies the behavior of a system.

Packet ● (core concept) — A chunk of data plus metadata, used to route the data between origin and destination and to reassemble the data stream. Packets may arrive at the destination in order, out of order, or not at all.

IP, TCP, and UDP ● (core concept) — Common protocols used on the Internet for addressing and transporting packets of data.

World Wide Web ● (core concept) — A system of linked pages, programs, and files. The Web uses the Internet but is distinct from it: the Internet is the underlying network of networks, while the Web is a service built on top of it.

HTTP ● (core concept) — A protocol used by the World Wide Web to request and deliver its linked pages, programs, and files.

Scalability ● (core concept) — The capacity of a system to change in size and scale to meet new demands. The Internet was designed to be scalable, which is why it could grow to billions of devices.

Fault tolerance ● (core concept) — The property of a system that can support failures and still continue to function. The Internet was engineered to be fault-tolerant, which matters because elements of complex systems fail at unexpected times, often in groups.

Redundancy ● (core concept) — The inclusion of extra components that can take over if other components fail. On a network, redundancy means having more than one path between devices, so data is rerouted when a device or connection fails; it requires additional resources but provides fault tolerance and reliability.

Sequential computing ● (core concept) — A computational model in which operations are performed in order, one at a time. A sequential solution takes as long as the sum of all of its steps.

Parallel computing ● (core concept) — A computational model in which a program is broken into multiple smaller sequential operations, some of which are performed simultaneously. Such a solution takes as long as its sequential tasks plus the longest of its parallel tasks, and parallel solutions scale more effectively than sequential ones.

Distributed computing ● (core concept) — A computational model in which multiple devices are used to run a program. It allows problems to be solved that a single computer could not handle because of processing time or storage needs, and solves large problems more quickly than one computer could.

Speedup ● (core concept) — A measure of a parallel solution's benefit: the time the task took sequentially divided by the time it took in parallel. Solution efficiencies are compared by the time they take to perform the same task.

Sequential-portion limit ● (core concept) — The observation that a parallel solution consists of a parallel portion and a sequential portion, so efficiency is still limited by the sequential part: at some point, adding more parallelism no longer meaningfully increases efficiency.