This article reveals a dark secret: most of LAVA’s spec sheets are wrong, and we’re not going to change them.
A little while back I learned a piece of computer history that brought this to light. Don’t worry, it won’t change anything you do, but it is a case study in the evolution of language, if that’s your thing.
DB or not DB? That is the question.
LAVA has a large number of serial port products, as you know. Most of these have RS-232 serial ports, with the familiar DB-9 connector:
DB-9 or DE-9? Your call
At least, so I’ve always thought. But I recently read something that made me realize that I’ve been wrong all along: what I thought were DB-9 connectors are not DB-9 connectors. Let me tell a story.
Once upon a time, 1952 to be exact, ITT Cannon (a division of ITT Corporation) developed a standard for a group of connectors they called “D-subminiature connectors”. At the time, these connectors were considered small enough to merit the term “subminiature”; today, they are among the largest connectors in common use.
When the standard was created, its enumeration of designs was logical enough: the letter “D” designated the shape of the metal shield that encircled the pins or sockets; a second letter (A, B, C, D, or E) designated the size of that shield; a numeral designated the number of contacts the connector had; and a final letter (P or S) indicated those contacts were either “plugs” or “sockets”. A labelling system that was perfectly logical, complete, and unambiguous. And doomed to confusion, as we will see.
In this original system the number of pins tended to determine the size of the connector overall, and a series of connectors was created. The basic line-up was:
This worked well enough until the personal computer got into the mix, in the 1980s. At that time, the RS-232 serial port on these systems was a DB-25P port, with the full complement of serial pins; what we often call a “male” connector. In fact, the LAVA SSerial-550 adapter card, our longest-running product, still employs this connector, as does our SSerial-PCIe.
The parallel port on these early personal computers was a “socket” connector (or “female” connector), also in a DB-25 shell.
All was fine until it became clear that the full range of serial pins was often not necessary, at which point serial ports on PCs mostly switched to the D-subminiature 9-pin connector, the DE-9P. But, by analogy with the naming of the DB-25 connectors already being used, people mistakenly ended up calling the smaller connectors “DB-9” connectors. It’s like calling everyone “Henry” who resembles the first “Henry” you come to know.
It doesn’t help the complication that the D-subminiature standard also has a second series of connectors called “high density” connectors. Along with the variety of shell sizes therefore, the number of rows of pins in a connector can vary, with high density connectors usually having three rows. These high density connectors’ designations use the same “D” in the first position, and the same letter designations in the second position, with a numeral defining the number of pins, just as before. Now we have a high-density DA shell with 26 positions (pins or sockets), a high-density DB shell with 44 positions, a high-density DC shell with 62 positions, and a high-density DE shell with 15 positions. Note that there is no high-density connector configuration for the DD shell, maybe because the original DD shell already had three rows of pins, but don’t quote me on that:
And now here’s where video connectors come in: the 15-pin connector used for VGA video on personal computers came to be called a DB-15, when in fact its shell is the “E” size shell. And, with its three rows of pins, it is in reality an HD DE-15P (on the cable).
By now, you should be thoroughly confused, but you can relax. In practice, the misnamed connectors are so prevalently misnamed that their proper names are seldom recognized for what they are. Keep calling them what you have been calling them since before you read this article, we’ll keep our spec sheets the same, and nobody gets hurt.