Which of the following components found in a legacy server has a 16-bit bus?

The component found in a legacy server that has a 16-bit bus is the ISA (Industry Standard Architecture) bus. ISA was widely used in older computing systems, particularly in the early days of personal computers and servers. It was introduced in the 1980s and typically operated with two different bit widths: a more common 8-bit bus, but it was later extended to a 16-bit bus in the ISA 16 specification. This allowed for greater data throughput compared to the original 8-bit architecture.

The other components listed do not utilize a 16-bit bus format. USB (Universal Serial Bus) is a serial interface and does not adhere to a traditional bus width like those found in parallel architectures. PCI (Peripheral Component Interconnect) is a bus standard that supports 32-bit and 64-bit width but not strictly 16-bit. AGP (Accelerated Graphics Port) is specifically designed for graphics cards and operates with a 32-bit bus architecture. Therefore, among the choices provided, ISA is distinct in that it is a legacy bus standard with a 16-bit variant.