This is a common connector used in many computer, audio/video, and data applications. The official name is D-subminiature, but many people call it “D-sub” or just “DB”. The connector gets its name from its trapezoidal shape that resembles the letter “D”. Most DB connectors have two rows of pins. Common types of D-sub connectors are DB9 and DB25, used on PCs for serial and parallel ports.

One special type of D-sub connectors is the High-Density DB style, which looks just like a regular DB connector, only with pins that are slightly smaller and placed closer together. This is typically referred to as an “HD” connector. HD connectors often have three rows of pins instead of two. The most common HD connector is the HD15, which is found on PC video cards and monitors. DB- and HD-connectors use thumbscrews to secure the connector in place.

Another type of D-sub is the MD, or Micro DB connector. This connector is slimmer than a standard D-sub, with pins even smaller than the ones used on HD connectors. The MD is also commonly called a “half-pitch” DB connector. These are often used in SCSI applications, and the most popular types are the MD50 and MD68 connections. MD-connectors can use latchclips or thumbscrews as anchoring mechanisms.

D-sub connectors are usually described by the total number of pins that they can hold. In some cases, a DB25 connector may only have 4 or 5 pins loaded into it; however, it is still called a “DB25” connector and not a “DB4” or “DB5”. Another example is the HD15 connector used by monitors—most monitor cables only are loaded with 14 pins, but it is still called an HD15 connector. 

DB9

  This interface is commonly used for RS-232 serial applications. For several years, DB9 ports were standard equipment on PCs; nowadays, many newer computers are being built without them. On a PC, the serial port is a DB9 male. A DB9 connector has 9 pins arranged in two rows, with one row on top of the other. The top row has 5 pins and the lower row has 4 pins. 

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DB25  

  DB25 connectors are most often used for parallel, RS-232 serial, or SCSI applications. A PC normally has one DB25 female parallel port. On older PCs, a DB25 serial port could sometimes be found instead of a DB9. DB25 SCSI connections are female, and can be found on older Apple computers as well as on expansion cards for SCSI peripheral devices. 

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DB15      

  This connector can be found on sound cards, older AUI network cards and devices, and on legacy Macintosh monitors. A DB15 has two rows of pins: 8 on the top, and 7 on the bottom. Don't confuse it with the HD15, which has three rows. 

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DB37     
  This connector is used sometimes with Cisco networking hardware, and other applications that use RS-449 serial communication. The top row has 19 pins, the bottom row 18. 

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HD15     

  A very common connector used mostly as a video interface for computers and monitors. The HD15 is a High Density DB-style connector, so it can also be called an HD DB15. Another popular name is “VGA connector”, although it is used in video applications that support much higher resolutions (SVGA, XGA, UXGA, etc.). An HD15 connector is the same size as a DB9 connector, but it has three rows of 5 pins. On most HD15 male connectors, there is one pin (pin #9) missing in the middle row. 

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MD50     
    
  The MD50 connector is used primarily with SCSI devices. Some alternate terms for this connector include HD50, HD DB50, and SCSI-2 50-pin. The MD50 has two rows of 25 pins. The pins are very small, and placed closely together. Most MD50 connectors use squeeze-latches to hold the connection in place. 

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MD68     
  The MD68 connector is similar in shape to an MD50, but has more pins. Its pins are also arranged in two rows, each row with 34 pins. MD68 connectors are very common on SCSI devices, and they are sometimes referenced as HD68, HD DB68, SCSI-3, or Wide SCSI connectors. Some MD68 connectors have latchclips, but most use thumbscrews.