Wednesday, February 11, 2009

Still Key Jammin', 19 years later!

I was just re-reading a piece of code that I'd written earlier today which attempts to detect duplicate customer records in a particular database table, when I came across a misspelling in a comment: I'd misspelled the word "duplicate" as "dupliate."  I corrected the typo, and continued reading, when I came across another instance of the same misspelling: "dupliate" instead of "duplicate." 

Curious now, I did a search of the source file for other instances of the misspelled word "dupliate"; to my surprise, I found a LOT of instances of that misspelling (all in my own hand-entered comments, so not due to intellisense or copy-paste)!  At this point, I suspected that the problem was due to some factor beyond simple human error, so as an experiment, I tried just typing the word "duplicate" several times in a row (and paying attention to be sure that I actually was hitting the C key).  This was the output:

dupliate dupliate dupliate dupliate dupliate duplicate dupliate

The problem was reproducible almost every time.  I briefly experimented further:

  • The problem WAS reproducible in text editors other than my IDE (Eclipse). 
  • The problem was NOT reproducible when I typed slowly and deliberately, being sure to hit each individual key one at a time.
  • The problem was NOT reproducible using my machine's built-in keyboard (an IBM/Lenovo Thinkpad T60 laptop); only when using the external keyboard (a "standard" qwerty / U.S. layout black Dell-branded PS/2 keyboard, part number 04N454).

I discovered that the specific problem was that while the L and I keys on the keyboard were being pressed, presses of the C key would be dropped/ignored.  I found that every other letter key on the keyboard worked with L and I held down; just not C!

So what was happening here was that in typing "duplicate," I apparently was typing the C (with my left hand) before I'd let go of the L and I keys (with my right hand) -- or at least before the L and I keys had "popped back up" -- and consequently, the C key press was getting dropped.

Now that I'd realized what was going on, I remembered that this is a typical hardware limitation of keyboards: certain keys cannot be pressed in combination with one another.  I hadn't thought about this in years and years -- since back when I used to play 2-player games on the PC that would have both players using the keyboard on the same PC simultaneously.  The old (1990) PC game Star Control actually came with a utility called "Key Jamming" for working around this very issue: The utility would allow you to experimentally hold down various key combinations, and tell you which ones the PC could "see," to allow you to customize the game's keyboard controls on your machine's keyboard such that players in a two-player game wouldn't end up "locking out" one another.

It's unfortunate that the Dell 04N454 keyboard has this particular limitation.  I'm not sure what I can do to work around it, though, short of just needing to have extra awareness of my spelling (particularly in non-spell-checked environments such as IDEs) -- or else looking into using a different keyboard which isn't affected by this particular limitation!


  1. Extra keyword to help find this post in the future: "lic"

  2. Note to self: The Microsoft RT2300 has the exact same issue with "lic", so this problem isn't limited to Dell keyboards.

  3. I'm now using a Das Keyboard Model S Professional Silent (, which is not affected by this issue (or any other similar issue)!


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