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The drum is a metal cylinder, usually aluminium, which is coated with a special material, known as a
photoconductor.
This material has the property of being to store an electrical charge on its surface in darkness. In order to charge the drum, it is rotated against an insulated roller which has a voltage of 6000 volts applied to it. This coats the drum surface in a uniform electrostatic charge.
The photoconductor also has the property of being able to lose the charge on any area which is struck by laserlight. The laser fires pulses of light via the rapidly spinning mirror across the rotating drum, wiping non image areas and leaves an invisible image composed of electrostatic charge on the drum surface. This process is called exposure.

The drum now has the image written on it in invisible electrostatic charge. Big deal, you say, whats the use in that? Well, In order to make use of the image it has to be made visible and the process of making the image visible is known as development. Inside the cabinet, mounted close to the drum is a unit called the toner carousel. This unit can rotate bringing one of four different rollers into contact with the charged drum surface. Each of the rollers is coated with a special powder called toner.
The toner is negatively charged, which makes it stick to the charged image areas on the drum as it rotates past. This makes a visible powder image on the drum surface. Remember how the image processing unit(above) split the image into its cyan, black, magenta and yellow components, and how each of these components was printed onto the drum in electric charge via the laser?
Well, the toner carousel is rotated to bring each invisible charge image into contact with its appropriate coloured toner in order to make four different coloured images on the drum surface, one after the other. Each of the different coloured images has to be laid precisely on top of each other in order to reintegrate the full colour image and this process is called transfer.

As each coloured image is produced on the drum, it is transferred onto
a synchronised moving rubber belt which lightly contacts the drum
surface. Just at this point, below the belt is another insulated roller which is charged to 6000 volts. This roller attracts the toner off the drum and holds the powder image on the belt with electrostatic charge. Each coloured image is laid precisely on top of each other by the use of complicated digital electronics and precision timing components. A deviation of as little as 0.1mm in the placement of each layer would result in a ruined image. Considering the fact that each image is made of powder grains about the same size as smoke particles, the fact that there are four images, all the different mechanical and electrical systems liable to jitter and variation, its nothing short of a miracle that the damn thing works at all!

How`s your brain managing? Bet you wish you`d paid more attention to your physics teacher. Anyhow, we now have a perfect image made of powder
particles held onto a rubber belt
running around inside our colour printer. How do we get that onto a sheet of paper?
A single sheet is fed up from the paper tray and is timed so that it contacts the rubber belt at the point where the image starts. Another insulated roller below the paper is charged up to 6000 volts and attracts the image off the belt and onto the sheet. The
paper, with the image on it, still in powder form, drops onto a transport bed which feeds it to the final stage, where the toner is permanently bonded onto the sheet.

“Wow, this really looks complicated, not sure if I can be bothered getting into this”
is probably what you`re thinking now. And a colour laser printer is a very complicated piece of kit - In fact, it has so many moving parts all liable to jam, jitter or likely to go bust and a thousand reasons as to why it couldn`t possibly work, I often ask myself:

(1) What nutcase actually thought it up?
(2) How did the nutcase ever get it to work?
(3) Why does it work so well?
(4) Why didn`t I think of it?

But every complex system, when broken down into its basics, becomes easier to understand.,
so I`ve broken the process down into (hopefully) easy to understand chunks, detailed below.

All that remains is to permanently fix the powder image onto the paper. The sheet is drawn into a set of heated pressure rollers which melt and press the toner image into the paper and then feed the sheet out of the printer.