Ultra2WideSCSI

Ultra2WideSCSI, also known as LVD/SE (Low Voltage Differential / Single-Ended), is a version of the SCSI (Small Computer System Interface) parallel bus standard. It was introduced in the late 1990s as a successor to UltraSCSI standards. A key feature of Ultra2WideSCSI is its support for both Low Voltage Differential (LVD) and Single-Ended (SE) signaling modes. This dual-mode capability allowed for backward compatibility with older SE SCSI devices while also offering the significant performance and cable length advantages of LVD.

Ultra2WideSCSI operates at a speed of 80 megatransfers per second (MT/s). The "Wide" designation indicates that it uses a 16-bit data path, doubling the data transfer width compared to "Narrow" SCSI. This wider bus, combined with the higher speed, significantly boosts overall throughput. In LVD mode, Ultra2WideSCSI can support cable lengths of up to 12 meters (approximately 39 feet), a substantial improvement over the shorter lengths allowed by SE SCSI.

The LVD signaling uses differential signaling, which is more resistant to electrical noise and signal degradation, making it suitable for longer cable runs and higher speeds. Devices on an Ultra2WideSCSI bus must be terminated. In LVD mode, proper LVD termination is required, and the bus will typically operate in LVD mode if all connected devices support it. If an SE device is connected, or if there's a fault in LVD operation, the bus will automatically switch to SE mode, though at reduced speed and cable length limitations. Ultra2WideSCSI was widely adopted in servers, workstations, and high-performance storage subsystems before being largely superseded by serial interfaces like SAS and SATA.