Thursday, December 18, 2008

Lights on Computers

Hah!  Something just occurred to me.

In the old days, even in the 70s when I first became exposed to computers, it was normal to represent the contents of memory registers as blinking lights.  By the 70s these were red LEDs of course, which were lower power.

These days equipment has lights but it's usually a flashing LED for network activity on a port, power lights, run status lights, and such.

But what if a modern computer was attached to a display that had an LED for every bit in every CPU register!  What would that look like?  Well, at CPU speed the changes would be so fast that all of the LEDs would probably all glow at a nearly equal continuous glow.  If some bits were statistically more often a one or zero, they would be slightly brighter or dimmer than average.  So you'd actually have to, I suppose, just periodically sample register state to get actual blinking.

With 32-bit and 64-bit registers and lots of them, it would be an interesting display.  With today's absurd multi-colored LEDs, it would also be a pretty display.

LEDs are also absurdly bright now.  In the HPC ELLIPSE cluster at Emory, each X2200 had a bright green LED which was pretty much too bright to look at.  Due to the color of green and the brightness of these lights, I'm convinced they are the same LEDs that are used in green traffic lights.

They also had locator lights (which you can flash with software to find a particular machine—a common feature on high-density, clustered machines these days).  The locator light was a blueish white LED that's as bright as what they use in those new flashlights, meaning it was like a spot light!