HP 450c Service Manual - Page 189

Memory Usage It is difficult to calculate the amount of Printer memory needed to plot a drawing of any given file size. Memory is used, not just to hold the input data, but also for system overhead, processing workĆspace, and storage of the internal representation of the plot. Some types of graphics require relatively large amounts of memory. Examples are wide lines, raster fill patterns, polygons, and userĆdefined lines. Plot Orientation The output orientation of the drawing also has an impact on memory usage. Compare a plot of horizontal lines with one of vertical lines. Lines plotted parallel to the carriage axis take up considerably less memory than those plotted perpendicular to it. The Printer builds graphic display objects on a swathĆbyĆswath basis. A horizontal line can be contained in one swath. A vertical line spans many swaths and therefore requires more entries in the Printer's internal display list. Raster Image Processor The raster transfer language (RTL) provides a solution to insufficient memory on the Printer. When all the data is sent to the Printer in the order leftĆtoĆright and topĆtoĆbottom, the Printer is able to plot the data as it receives it. For this to happen, software (a rasterĆimage processor) in the computer must first rasterize all the data. The software issues a command (referred to in RTL as no negative motion) telling the Printer that it will not receive data for any media location on which it has already plotted. The use of no negative motion is called flow mode. Data flows through the Printer without being stored in a display list, so the size of the file that you can send is almost unlimited. Functional Overview HP DesignJet 430, 450C and 455CA Printers 10-9