twinax

Twinax, short for twinaxial, refers to a type of cable and associated signaling used for short-range, high-speed digital communications. It consists of two inner conductors embedded in a single outer shield, enabling differential signaling within one compact jacket. The design aims to combine the shielding advantages of coax with the speed and density benefits of parallel conductors, making it well suited for close-proximity interconnections.

Historically, twinax was widely used in IBM mainframe and minicomputer environments during the 1980s and 1990s. It supported connections between storage controllers, disks, printers, and other peripherals over relatively short distances with improved immunity to electromagnetic interference compared with some alternatives of the era. The cables and connectors were designed to preserve impedance and minimize signal reflections, which helped achieve higher data rates over short runs.

Construction and characteristics vary by generation and vendor, but twinax cables generally feature two insulated copper conductors within a single shielded sheath. Termination requires specialized twinax connectors and care to maintain the intended impedance. Data rates for twinax links ranged from hundreds of megabits per second to a few gigabits per second in practice, with performance limited by length, attenuation, and skew.

Decline and legacy: The rise of fiber optic and high-speed copper technologies led to a decline in twinax use outside legacy IBM environments. Today, twinax is primarily encountered in historical documentation and discussions of mainframe I/O architectures, though some niche or branded implementations may persist in specialized equipment where short, shielded copper paths remain desirable.