Overview
The Northbridge was traditionally the part of the chipset responsible for high-speed communication between the CPU, RAM, and the AGP or PCIe graphics bus.
Obsolescence
In modern computer architectures, the functions of the Northbridge have been integrated directly into the CPU (the 'Uncore' or 'System Agent'). This reduces latency and improves performance by shortening the physical distance data must travel.
Legacy
While no longer a separate chip on modern motherboards, the term is still used in historical contexts of computer architecture.