Bandwidth

Bandwidth is the maximum amount of data a network link or interface can transmit per unit of time. It is usually expressed in bits per second and their multiples: megabits (Mbit/s) or gigabits per second (Gbit/s). Bandwidth describes the theoretical "pipe width" through which data flows — the wider it is, the more information can travel in parallel during the same window.

How bandwidth works

Three commonly confused terms are worth separating:

• Bandwidth — the upper speed limit of a link, a property of the infrastructure.
• Throughput — the real, measured transmission rate, always lower than the theoretical maximum because of protocol overhead, packet loss and congestion.
• Transfer — the cumulative volume of data moved during a billing period, such as the monthly cap in a hosting plan.

Effective bandwidth also depends on latency, TCP retransmissions and window size. That is why a 1 Gbit/s link rarely reaches the full 125 MB/s — real-world results usually land at 70–90% of the nominal figure.

Bandwidth in practice

Bandwidth is a key parameter when choosing infrastructure and planning traffic:

1. Hosting and VPS — a server's network port (e.g. 1 Gbit/s) determines how many concurrent downloads it serves without slowdown; a VPS or dedicated server typically states both the port speed and a monthly transfer allowance.
2. Streaming and files — video, backups and large downloads consume bandwidth fastest and demand headroom.
3. Offloading the link — a CDN serves static assets from edge nodes close to users, saving origin-server bandwidth.

When monitoring performance, bandwidth is read alongside TTFB and CPU usage — only the full set of metrics reveals whether the bottleneck is the link, the disk or the application.