Which hard drive specification has the fastest theoretical bus speed?

The hard drive specification with the fastest theoretical bus speed is NVMe (Non-Volatile Memory Express) over PCIe (Peripheral Component Interconnect Express). NVMe drives can leverage multiple PCIe lanes, with current iterations supporting up to PCIe 4.0 and PCIe 5.0, allowing for speeds of up to 32 Gbps per lane or more. This results in significantly higher data transfer rates compared to traditional SATA drives, which are limited to around 6 Gbps. Overall, NVMe over PCIe provides the highest performance for storage solutions.