Firewire - Comparison With USB

Comparison With USB

While both technologies provide similar end results, there are fundamental differences between USB and FireWire. USB requires the presence of a bus master, typically a PC, which connects point to point with the USB slave. This allows for simpler (and lower-cost) peripherals, at the cost of lowered functionality of the bus. Intelligent hubs are required to connect multiple USB devices to a single USB bus master. By contrast, FireWire is essentially a peer-to-peer network (where any device may serve as the host or client), allowing multiple devices to be connected on one bus.

The FireWire host interface supports DMA and memory-mapped devices, allowing data transfers to happen without loading the host CPU with interrupts and buffer-copy operations. Additionally, FireWire features two data buses for each segment of the bus network whereas USB only features one. This means that FireWire can have communication in both directions at the same time, whereas USB communication can only occur in one direction at any one time. Thus it may be no surprise that while USB 2.0 is quoted as running at a higher signaling rate (480 Mbit/s) than legacy FireWire 400 (400 Mbit/s), data transfers over S400 FireWire interfaces generally outperform similar transfers over USB 2.0 interfaces in real world environments. Few if any USB 2.0 device implementations are capable of saturating the entire 480 Mbit/s, but this can be achieved with multiple devices on the same bus. In real world tests USB hosts rarely can sustain transfers exceeding 280 Mbit/s, with 240 Mbit/s being normal.