Colour laser printers come in two flavours. The industry terms are
four-pass, and single-pass. Oops, guess which we have here in the
DocuColor 12?
I'm not saying any of you are absolutely wrong. In fact, I think
you've all got a piece of the puzzle. But I think Elmo got the
biggest piece in this particular case.
Effective throughput of a printer is dependant on quite a number of
variables. Document complexity, duplex/simplex, input bandwidth, and
yes, engine speed can all affect throughput, depending on the severity
of the condition. Resolution can cause a change in absolute engine
speed, but this usually occurs only between print jobs (600 dpi and
1200 dpi image mode on a mono Lexmark Optra, for example). Also, if
you try to feed your fast, 60 ppm printer a 1200 dpi, image-laden
data stream across a 9600 bps serial line, of course it will choke,
big time! This is one of many reasons that can cause a printer
stall, so-called because it results in the engine stopping, even
momentarily. In our business, the fastest we can drive workgroup
lasers across our national network during peak hours, with all kinds
of other online traffic, is about 35-45 pages per minute. Putting a
bigger printer on the end of that pipe accomplishes absoluting
nothing, unless we pump up the bandwidth. However, local performance
might still be outstanding.
But that's not what is happening here.
Early colour lasers (and now 'value-level' colour lasers) are
four-pass devices. Available technology at the time allowed only one
colour to be imaged at a time, required four full passes of the media
(either the transfer drum/belt, or the paper) to image all four
colours (CMYK). These devices differentiated only between colour and
monochrome print jobs, not by pages. Either the job was a single-pass
monochrome, or it was four-pass colour. There is no 2-pass, or 3-pass
mode, no in-between speed. If any colour was called for on any page,
the printer's effective throughput for the entire print job would be
reduced by a factor of 4 because of the 4-pass operation. There's
your speed difference. The DocuColor 12 is an earlier, four-pass
printer. The first 4-pass I encountered, was the Xerox 4700 II (Huge,
300 dpi floorstanding model rated at 7.5 ppm colour, 30 ppm
monochrome). A more recent desktop example is the Lexmark C710 -
loud and clunky as the cartridges rotated to the next colour between
passes. A current example of a value four-pass is the Xerox Phaser
6120.
Current technology has rendered the four-pass almost obsolete, except
for value devices. Most colour lasers are now single-pass devices,
which allow full imaging of all 4 colours (CMYK) in a single pass of
the media. These devices usually have matching colour and monochrome
speeds, and they're a lot quieter. Some models may be slightly
faster at monochrome, based on printer design, because the paper path
may be shorter due to bypassing colour imaging stations. Current
example of such a single-pass device: Xerox Phaser 6350.
Here's a recent review of 3 'value' colour lasers, two single-pass
devices, and a four-pass device... interesting.
http://www.crn.com/sections/hp/hp.jhtml?articleId=175701284
Regardless, the absolute print engine speed in both one-pass and
four-pass devices should be constant, all other variables being
equal, and non-detrimental to performance.
