The closer to the server the higher speeds can be obtained by the client operating system. Generally the ultimate speed limit is not the server speed but the distance to the server. They are currently capable of running from 300 megabit for the smaller servers to over 2 gigabit for the faster servers. The servers are dedicated to speed testing and monitored for performance. This can be limited by several factors including the distance to the test servers, the operating system in use, the traffic en-route, and of course any congestion or wiring problems close to your location. The speed test attempts to take your network connection to its maximum speed. Speeds are quoted in megabits per second (1 million bits per second) or kilobits per second (1000 bits per second) of data. The test should take no longer than one minute to complete. It does a multiple stream download and upload to servers it determines may be closest to your location. A speed test checks the maximum speed of your connection to a remote server on the internet.

Ookla speed map