Mike's PCjr Page

On the back of the PCjr I was looking at the ports. I couldn't remember what the "L" port was for. I couldn't find it in the Tech Ref, Googled it, and found out it was a spare and not connected to anything on the system board?

Are there any thoughts about what was intended for this? Why label it "L". If it was a spare, I would have expected them to leave it blank...

There’s also an unused jack reserved for future expansion (labeled “L” for “Later,” explained an IBM spokesman).

— “Report on IBM’s New PCjr”, Compute!, January 1984, p. 48.

But I, too, would like to know what use IBM had in mind for a soldered-in connector that’s not electrically connected to anything on the motherboard except ground.

I never looked at it -- I just assumed it was connected to some signal line. If it's really connected to only ground, that's pretty funny.

I always thought it was a light pen port but never gave it much thought, not caring much for light pens.

That’s the LP port...

The joke at the time was that "L" stood for "Later."

Pretty sure it's a Light Pen port.

"LP" is for the light pen. "L" is just unused .. hence the "Later" joke.


Mike