A D-sub contains two or more parallel rows of pins or sockets usually surrounded by a D-shaped metal shield that provides mechanical support and some screening against electromagnetic interference. The D shape guarantees correct orientation. The part containing pin contacts is called the male connector or plug, while that containing socket contacts is called the female connector or socket. The socket's shield fits tightly inside the plug's shield. The shields are connected to the overall screens of the cables (when screened cables are used), creating an electrically continuous screen covering the whole cable and connector system.
D-subminiature connectors were invented by ITT Cannon, part of ITT Corporation, in 1952. Cannon's part-numbering system uses a D as the prefix for the whole series, followed by a letter denoting the shell size (A=15 pin, B=25 pin, C=37 pin, D=50 pin, E=9 pin), followed by the actual number of pins, followed by the gender (P=plug, S=socket). For example, DB25 denotes a D-sub with a 25 position shell size and a 25 position contact configuration. The contacts in these connectors are spaced approximately apart with the rows spaced apart.
Cannon also produced D-subs with larger positions in place of some of the normal pin positions that could be used for either high-current, high-voltage, or co-axial inserts. The DB13W3 variant was commonly used for high-performance video connections; this variant provided 10 regular (#20) pins plus three coaxial contacts for the red, green, and blue video signals.
In the photograph below, the connector on the left is a 9-pin (DE-9) connector plug, and the one on the right is a 25-pin (DB25) socket. The hexagonal pillars at either end of each connector have a threaded stud (not visible) that passes through flanges on the connector, fastening it to the metal panel. They also have a threaded hole that receives the jackscrews on the cable shell, to hold the plug and socket together.
Possibly because the original PC used DB25 connectors for the serial and parallel ports, many people, not knowing the significance of the letter "B" as the shell size, began to call all D-sub connectors "DB" connectors instead of specifying "DA," "DC" or "DE." When the PC serial port began to use 9-pin connectors, they were often called "DB9" instead of DE9. It is now common to see DE9 connectors sold as "DB9" connectors. DB-9 is nearly always intended to be a 9 pin connector with an E size shell.
There are now D-sub connectors which have the original shell sizes, but more pins, and the names follow the same pattern. For example, the DE15, usually found in VGA cables, has 15 pins, in three rows, in an E size shell. The full list of connectors with this pin spacing is: DE15, DA26, DB44, DC62, and DD78. Alternatively, following the same confusion mentioned above in which all D-sub connectors are called "DB", these connectors are often called DB15HD, DB26HD, DB44HD, DC62HD, and DD78HD, where the "HD" stands for "high density". They all have 3 rows of pins, except the DD78, which has 4.
A series of D-sub connectors with even denser pins is called "double density", and consists of DE19, DA31, DB52, DC79, and DD100. They have 4 rows of pins.
There is yet another similar family of connectors that is easy to confuse with the D-sub family, but is not part of it. These connectors have names like "HD50" and "HD68", and have a D-shaped shell but the shell is about half the width of a DB25. They are common in SCSI attachments.
The suffixes M and F (male and female) are sometimes used instead of the original P and S (plug and socket).
The original D-subminiature connectors are now defined by an international standard, DIN 41652.
The widest application of D-subs is for RS-232 serial communications, though the standard did not make this connector mandatory. RS-232 devices originally used the DB25 25-pin D-sub, but for many applications the less common signals were omitted, allowing a DE9 9-pin D-sub to be used.
On PCs, 9-pin and 25-pin plugs are used for the RS-232 (serial) ports and 25-pin sockets are used for the (parallel) printer ports (instead of the Centronics socket found on the printer itself). 25-pin sockets on Macintosh computers are typically SCSI connectors (again in contrast to the Centronics C50 connector typically found on the peripheral).
A male DE9 connector on the back of an IBM-PC-compatible computer is typically a serial port connector. IBM introduced the DE9 connector for RS-232 on PCs with the Personal Computer AT in 1984. A female 9-pin connector on the same computer may be a video display output: monochrome, CGA, or EGA. Even though these all use the same connector, the displays cannot all be interchanged and monitors or video interfaces may even be damaged if connected to an incompatible device using the same connector. Later analog video (VGA and later) adapters replaced these connectors by DE15 15-pin high-density sockets, which have three rows of five contacts each in the space that was previously occupied by two rows of five and four contacts. Other common names for DE15 connectors are HD15, where HD stands for High Density, and (less accurately) DB15 and DB15HD.
From the late 1970s and all through the '80s, DE9s without the pair of fastening screws were used as game controller connectors in a variety of video game consoles and home computers, quite possibly due to the success of the Atari 2600 game console. Computer systems which use them include the Atari 8-bit and ST lines; the Commodore 64, 128, and Amiga; the Amstrad; the SEGA Master System and Genesis. They were not used in the Apple and PC systems and most newer game consoles. Used in the standard way, they support one digital joystick and one pair of analog paddles; on many systems a computer mouse or a light pen is also supported through these sockets, however these mice are not usually exchangeable between different systems. DE9 connectors are also used for some token ring and other computer networks. DA15 is used for Ethernet Attachment Unit Interface.
Many uninterruptible power supply units have a DE9F connector on them, in order to signal to the attached computer. Often these do not send data serially to the computer but instead use the handshaking control lines to indicate low battery, power failure or other conditions. Such usage is not standardized between manufacturers and may require special cables to be supplied.
The complete range of D-sub connectors also includes 15-pin DA15s (two rows of 7 and 8); 37-pin DC37s (two rows of 18 and 19); and 50-pin DD50s (two rows of 17 and one of 16), the last two being used in industrial products. The 15-pin DA15 has been notably used for color video output on early Macintosh computers and as the IBM-defined analogue joystick port on PCs (where it is female). Many third-party PC sound cards, particularly the Sound Blaster line from Creative Labs, included a variation of the IBM joystick port using the same connector but taking two of the pins to add a (usually MPU-401 compatible) MIDI interface. The DA15F was also used for the AUI connectors included on Ethernet cards in the 1980s and 1990s, albeit with a sliding latch to lock the connectors together instead of the usual hex studs with threaded holes. Finally, the early Macintosh and Apple II line of computers used a very rare 19 pin D-sub for connecting to external floppy disk drives, and the Commodore Amiga used an unusual 23-pin version for both its video output and for connecting an external floppy drive.
TASCAM used DB25 connectors for their multi-track recording audio equipment (TDIF), and Logitek Audio later did the same for its broadcast consoles, though with different pinouts. A few patch panels have been made which have the DB25 connectors on the back with phone jacks (or even TRS jacks) on the front, however these are normally wired for TASCAM, which is more common outside of broadcasting.
In broadcast and professional video, "parallel digital" is a digital video interface that utilizes DB25 connectors, per the SMPTE 274M specification adopted in the late 1990s. The more common SMPTE 259M "serial digital interface" (SDI) utilizes BNC connectors for digital video signal transfer.
D-sub connectors exist in at least five types, differentiated by the method used to attach wires to the contacts. These are solder-cup or solder-bucket, insulation displacement, crimp, PCB pins, and wire wrap.
A smaller type of connector derived from the D-subminiature, and about half the linear size, is called the microminiature D, or micro-D, which is a trademark of ITT Cannon. This connector is used in industrial instrumentation products. A few manufacturers make nano-D connectors, which are about half the size again.
The 25 pin D-Sub connector has become the standard in the recording studio industry for multi-channel analog audio and AES Digital audio.
The D-sub connector family is now in decline for general usage in the computer industry, for several reasons: cost, size, and lack of flexibility. For portable devices such as PDAs, MP3 players or mobile phones, the D-sub connector is usually too large to fit. Many laptop computers, where weight and size are crucial, no longer include D-subs. Even small form factor desktop PCs may find D-sub connectors too large for their value.
Because of the relatively complex shapes and assembly, especially the shaped metal D shield, and screws and nuts for physical securing, D-sub connectors are now quite expensive compared to other common connectors, which are mostly simpler. In the retail PC world where margins are very thin, these connectors are a natural target for removal.
The physical design is not friendly to plug-and-play applications. Thin metal pins, especially in higher-density connectors, are easily bent or broken, especially when frequently plugged in "blind" behind equipment. Although ESD and EMI resistant D-sub connectors exist, the fundamental design was never intended to protect from electrostatic discharge or electromagnetic interference or facilitate very high frequency interconnections.
For video purposes, the DE15HD connector is being slowly replaced by DVI and HDMI connectors, although this transition is proceeding more slowly, since many analog CRT monitors are still in use and the digital DVI connector is not useful for those.