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I remember that 20 years ago (around the year 2000) I came across a few computers with a weird monitor connector. They weren't old computers, but rather budget mainstream computers of the time period. I believe that one of them was a Pentium 3 or a Celeron.

The connector was very similar to standard VGA 15-pin connector, but the pins were laid out in 2 rows instead of 3. I don't remember how many pins there were, but I remember that I was surprised that it looked very similar to the standard COM port (RS-232) connector. However the monitor at the other end was a very standard CRT monitor (for the time). I think the connector was also for the on-board graphics on the motherboard, not a separate graphics adapter.

I'm curious as to what kind of standard that was. I can't find it on the Internet.

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    @JonCuster - That was what jogged my memory and inspired this question! :)
    – Vilx-
    Commented Jan 11, 2023 at 14:45
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    Mini-VGA uses two rows but I wouldn’t expect that in a budget PC at the turn of the century.
    – Stephen Kitt
    Commented Jan 11, 2023 at 14:53
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    The Macintosh and monitors for it used a DB-15 connector similar to that of a game port. I wouldn't find it astonishing if there existed some PC graphics cards that used the same connector.
    – supercat
    Commented Jan 11, 2023 at 16:42
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    @Justme: Hmm... a web search shows things being sold as DB-15 which look like the connectors in question. Maybe the terminology isn't correct, but it's a connector with the same pin spacing as DB-25 and DB-9, but with rows of eight and seven pins.
    – supercat
    Commented Jan 11, 2023 at 17:44
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    @supercat Yes, that is a common problem and people use wrong names. The letter means the connector shell size and the number means pin count. You have DE-9 for EGA and DE-15 for VGA, DA-15 for game port, and DB-25 for parallel port.
    – Justme
    Commented Jan 11, 2023 at 17:50

5 Answers 5

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Could it be CGA, MDA or EGA connector (DE-9) (as in https://en.wikipedia.org/wiki/List_of_video_connectors#D-subminiature_family) ?

The Pentium !!! era doesn't match, but on Wikipedia, there is this note that states :

Early VGA cards also used this connector

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  • I'm pretty certain that it wasn't that old. Definitely after 1997, and the computer was a consumer-grade middle-to-low-end PC. Windows 95 or 98. The monitor was a full-color CRT (don't remember the resolution, but definitely 16 or 32 bit full color).
    – Vilx-
    Commented Jan 11, 2023 at 14:49
  • I TEND to remember a DE-9 for a monitor. But it would have been at best for a 486 computer, maybe even a 286. Forgive my - lacky - memory: it was more than thirty years ago^^
    – Olivier
    Commented Jan 12, 2023 at 10:31
  • @Olivier It MIGHT have been a Trident TVGA8800CS : 16-bits ISA, DB-15 and DE-9. Still, 1988. And definitely discrete video card.
    – Olivier
    Commented Feb 28, 2023 at 7:55
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One option is that it was a Matrox video card which had a VGA connector and additional connector for the Rainbow Runner Studio daughter board. Though it was 15-pin DA-15 connector like used for Game/MIDI port and for Ethernet AUI port, not 9 pin DE-9 like used for RS-232 mouse.

Some early VGA cards did use DE-9 for VGA, and also some early cards had also a DE-9 for backward compatibility with older EGA/CGA/MDA monitors, but the time frame of about 2000 did not have those any more.

A similar looking video connector would be the Japanese D-terminal connector, but unlikely too.

Some cards had all kinds of custom ports for TV and 3D glasses but unlikely again to be DE-9 as that era started to use the Mini-DIN for anything television related.

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  • I distinctly remember that the monitor itself connected to the weird port. And no, it wasn't the Japanese D-terminal.
    – Vilx-
    Commented Jan 11, 2023 at 22:07
  • The monitor was purchased around 1994/1995 (486 to Pentium era) I don't know exactly as it was my employer that had bought it. I just kept the computer and the monitor when I left the company in compensation of what they owed me.
    – Patrick Schlüter
    Commented Jan 13, 2023 at 8:46
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The 1984 Professional Graphics Controller used a DE-9 connector (the same connector as MDA, CGA and EGA) with analogue signals compatible with those used later by VGA. A similar 9-pin connector was used by 32-bit Acorn computers in the late 1980s. It appears also to have found its way onto some PC video cards, as it is documented on various websites as "9-pin VGA".

All implementations seem to follow the PGC pinout, except that they have separate horizontal and vertical sync where the PGC has a single composite sync signal:

  1. Red video
  2. Green video
  3. Blue video
  4. Horizontal sync (PGC: composite sync)
  5. Vertical sync (PGC: either not connected, or select 400/480 lines)
  6. Red ground
  7. Green ground
  8. Blue ground
  9. Sync ground
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  • OP says budget mainstream computers but this PGC was very obscure and expensive. Are you saying it just because someone recently made a Youtube video mentioning it?
    – user20574
    Commented Jan 11, 2023 at 15:41
  • Why would you need/want a separate ground for each of RGB and sync?
    – Omar and Lorraine
    Commented Jan 11, 2023 at 16:28
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    @OmarL The analog monitor is supposed to have 75 Ohm input impedance. That means that ~10mA current flows through each of the red/green/blue video lines, and that currents needs to return to the graphics card through a ground line. The current through the ground conductor is dropping a voltage across the ground conductor, shifting ground potential. A high-quality video cable provides different ground conductors for red/green/blue (possibly as coax shields) and a high-quality monitor sends the return current through the individual pins and uses differential sensing. This will eliminate...
    – Michael Karcher
    Commented Jan 11, 2023 at 19:10
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    ... cross-talk between the color channels due to ground current from the other channels shifting a common ground potential.
    – Michael Karcher
    Commented Jan 11, 2023 at 19:11
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    @user253751 While 9-pin analog video on PC video cards is rare, a 9-pin input is commonly used on TTL/analog switchable CRT monitors, like the NEC MultiSync II (which is way more common than a PGC). In analog mode, they often use the variation of the PGC layout with separate sync (sometimes supporting CSYNC as well), so this is actual useful knowledge about "VGA on 9 pins".
    – Michael Karcher
    Commented Jan 11, 2023 at 19:31
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I have a Hyundai 17" monitor that has as input a DA-15. The cable has a normal DE-15 on one side and the very unusual DA-15 with 4 missing pins on the other side. The monitor also has a 5 BNC input (R,G,B,Vsync, Hsync) which allows to use the monitor if one would lose the very difficult to procure DA-15 to DE-15 cable.

I don't know if there was a graphic card or computer that used DA-15 as output but there is definitely a VGA monitor using as input.

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  • Nice! :) Now I'm starting to wonder if perhaps I remember the wrong end of the cable? It was over 20 years ago after all...
    – Vilx-
    Commented Jan 12, 2023 at 11:32
  • I can try to determine the pinout of the cable this week-end if people are interested.
    – Patrick Schlüter
    Commented Jan 13, 2023 at 8:52
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Could it be SGI's OpenLDI connector?

Somewhat more obscure port that looks like a cross-breed of SCART, serial port & VGA.

Couldn't find an English site, but this one has a photo of the connector and a display adapter:

https://www.journaldulapin.com/2017/03/31/sgi-1600sw/

When I started in computer science in -99, we had those SGI comps around with all sorts of weird interfaces.

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  • No, not really, sorry.
    – Vilx-
    Commented Jan 12, 2023 at 0:06
  • That's just an ordinary "Centronics" connector seen on any parallel port printer from the days before USB took over the world ;-)
    – TooTea
    Commented Jan 12, 2023 at 8:16
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    @TooTea No it isn't. OpenLDI uses the smaller MDR connector with 0.05" pitch. Printers used the larger MDR connector with 0.085" pitch. Besides many printers just used the same DB-25 instead of MDR before USB took over.
    – Justme
    Commented Jan 12, 2023 at 9:25
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    @Justme OK, didn't pay that much attention, but I would still describe it as "looks like a Centronics" than "a cross-breed of SCART, serial port and VGA" (which at least I can't readily visualize).
    – TooTea
    Commented Jan 12, 2023 at 9:35

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