This picture of punch cards strung for machine feeding linked to from sunfox's Flickr photostream, he owns the picture; made available under a creative commons license, CC BY-SA 2.0.
The First Iteration of the Difference Engine introduces my favorite steampunk fictional technology so far - the kinotrope!
The kinotrope is a large panel of little cubes with different colors on each facet, that can be mechanically spun to orient a specific color forward, making them physical pixels in a giant display.
The pixels are spun by steam powered crank machinery which is driven by a difference engine (which is, of course, the titular calculating machine. Difference Engines are not solely used to drive kinotropes, it is just one of their uses).
The Difference Engine reads a stack of punch cards in automated succession to map which pixels to spin at which time. As the cards are run through it, the pixels spin along in time.
It's just a cool device! I did some seraching to see if anyone ever tried to build something vaguely like this, and surprisingly, although it isn't powered by punch cards, someone has!:
This picture of Daniel Rozin's Wooden Mirror linked to from faroekat's Flickr photostream, he owns the picture; made available under a creative commons license, CC BY-NC-ND 2.0.
I'm going to just quote the flickr caption for the above photo, as it explains how this device works quite clearly:
Daniel Rozin's Wooden Mirror is also an example of audiovisual pixels. As you put your hand/face etc. over the camera (within the 'canvas'), the input translated the angle of each individual wooden pixel to become such that it reflects the amount of light tone that corresponds to the input. Each wooden pixel is connected to a servo-motor - so noise levels are very high.
This uses a camera instead of punch cards and a modern computer instead of a Difference Engine, but the wooden pixel display is exactly what Gibson and Sterling are describing in their novel. The description above even notes that the noise level of this display in motion is high, which was also suggested by the name the novel gives to people who program punch cards for the kinotrope: clackers.
Another note I loved about the description of the art/profession of clacking is that figuring out compression algorithms for the punch cards is a highly valued skill. Presumably you could just have one hole to represent each possible orientation of each colored cube. That would mean the data on the cards would be completely uncompressed, but for a screen of any size it would take forever to run all those cards through and set the machine.
In the book Sam Houston's kinotrope presentation is described as very cleverly animated, requiring rapid and precision timed spinning of the pixel cubes. This is made possible as Mick Radley has obtained expertly algorithmically compressed punch cards which are very highly valued. So highly, in fact, that possession of them precipitates several terrible crimes...