Bitcoin-Qt

Bitcoin-Qt was the name of the main Bitcoin software client from 2011 until early 2014, when version 0.9 renamed the project Bitcoin Core. The name referred to the Qt framework used to build its graphical interface. Today, Bitcoin-Qt survives as the name of the graphical program, bitcoin-qt, that ships alongside the headless bitcoind daemon in every Bitcoin Core release.

Why it matters

The renaming carried real significance. In 2013 and 2014 the network was growing quickly, and calling the dominant client simply Bitcoin blurred the line between the protocol and one program that implemented it. Adopting the name Bitcoin Core clarified that the software was one implementation of a shared protocol, not the protocol itself. The graphical client also mattered historically as the primary way early users held bitcoin: Bitcoin-Qt bundled a full validating node with a built in wallet, so ordinary users in the early years were, by default, running the network's infrastructure themselves.

How it works

The bitcoin-qt binary runs the same validation engine as bitcoind but presents it through windows and menus: a wallet view for sending and receiving, a transaction history, a peers panel, and a console for RPC commands. It downloads and verifies the full blockchain, which now exceeds 600 gigabytes unpruned, and can be configured to prune old block data to a few gigabytes for smaller machines.