DB-19

DB-19 is a D-subminiature electrical connector featuring 19 pins arranged in two staggered rows within a D-shaped metal shell. It was part of a standardized family developed by ITC Cannon in the 1950s, which became ubiquitous in computing and telecommunications for serial and parallel interfaces. While less common than its DB-9 and DB-25 counterparts, the DB-19 found important niche applications in specific computer systems and peripheral interfaces during the 1980s and early 1990s. Its design provided a robust, keyed connection for carrying multiple signal and low-power lines.

Overview

The DB-19 connector emerged from the broader D-subminiature standard, which was patented by ITC Cannon and became a De facto standard in the electronics industry. It was part of a series that included connectors like the DE-9 for RS-232 serial communication and the DB-25, which was widely used for parallel printer ports and early SCSI implementations. The DB-19 was typically used in contexts requiring more connections than a DE-9 but fewer than a DB-25, often for proprietary or system-specific buses. Its adoption was closely tied to the hardware design philosophies of several prominent computer manufacturers during the Home computer era, particularly for internal expansion or external disk drive connections.

Physical characteristics

A standard DB-19 connector consists of a D-subminiature shell housing 19 pins (male) or sockets (female), arranged with 10 pins in one row and 9 in the other. The shell, typically made of steel or aluminum with a chromate finish, provides EMI shielding and mechanical keying to prevent mis-mating. The contacts are usually gold-plated for reliability and are designed to mate with a corresponding connector that has a pair of jack screws for secure fastening. The pin spacing follows the standard D-sub pitch, and the connector is rated for a specific number of mating cycles, as defined in standards like MIL-DTL-24308. The physical layout made it suitable for both PCB mounting and cable termination applications.

Applications

The DB-19 connector is most famously associated with the external disk drive interface for the Apple IIc and Apple IIGS computers, where it connected peripherals like the Disk II and UniDisk 3.5. It was also used as the VGA monitor port on early PS/2 models like the IBM PS/2 Model 25 and IBM PS/2 Model 30, carrying analog RGB and sync signals. Other applications included certain SCSI-1 host adapter ports, proprietary network interfaces on older Sun Microsystems workstations, and as a control port for some Tektronix oscilloscopes. In telecommunications, it occasionally appeared in RS-422 serial implementations and for interconnecting modules in PBX systems.

Variants and compatibility

Several mechanical and gendered variants of the DB-19 exist, including the standard solder cup, right-angle PCB mount, and insulation-displacement contact types. A high-density version, following the HD-15 form factor but with 19 contacts, was never standardized, making true high-density DB-19 connectors rare. The connector is not pin-compatible with the more common DE-9 or DB-25, though passive adapters were manufactured for specific proprietary systems, such as adapting the Apple IIc disk port to use DB-25-based SCSI drives. Some third-party manufacturers produced cables with molded DB-19 ends for the Apple IIGS and PS/2 markets, and it was sometimes confused with the similarly sized but distinct DA-15 connector used for joystick ports and early Ethernet transceivers.

Historical context and adoption

The DB-19's development and use coincided with the rapid expansion of the personal computer industry in the 1980s, where manufacturers sought cost-effective, reliable connectors for expanding system capabilities. Its adoption by Apple for the Apple II series and by IBM for early PS/2 models provided it with significant visibility, though it was ultimately eclipsed by other standards. The rise of the DE-9 for serial communication, the HD-15 for VGA video, and smaller interfaces like the Mini-DIN connector on the Macintosh LC series reduced its relevance. By the mid-1990s, with the transition to PCI buses, USB, and DVI, the DB-19 had become a legacy connector, primarily of interest to collectors and maintainers of vintage computing systems like those from Commodore and Atari that also used it in limited roles.