Computer Systems and Networks

Computing devices connected together form a network, and the internet is a network of networks that works because everyone follows open protocols such as IP, TCP and UDP. Your data is split into packets that routers send along paths that can change. Bandwidth is the most data a connection can carry in a set time, usually measured in bits per second. The World Wide Web (linked pages sent using HTTP) is one service that runs on the internet.

Redundancy means having extra parts, like several possible paths between two devices, so the system keeps working if one part fails. Because packets can be rerouted around a broken connection or router, the internet is fault tolerant, though building in redundancy costs more.

Sequential computing does one operation at a time, parallel computing runs parts of a program at the same time, and distributed computing spreads a job across several computers. A parallel solution's time is the time for the steps that must run one after another plus the time of the slowest parallel piece, and speedup is the sequential time divided by the parallel time. For example, a 10-second step that must come first plus two 30-second steps run side by side takes 40 seconds instead of 70, a speedup of 70 ÷ 40 = 1.75; adding more processors can't remove the steps that must run in order.