Print capacity is actually a set of individual specifications that outline the mechanics of a printer's operation. Some of the characteristics that you should be familiar with are: CPL, CPS, print direction, dot configuration, resolution, pages per minute, warm-up time, and paper feed. The term CPL stands for Characters per Line, and is typically related to moving-carriage printers, such as impact or ink jet dotmatrix printers.
This is the number of characters that can fit onto a single horizontal line of text. You will likely find several entries under this heading-one for each type size (or style) that the printer can produce. A larger type size will result in fewer characters per line, and vice versa. For example, a type size that yields 10 CPI will fit 80 characters on an 8-inch horizontal line. At a setting of 15 CPI, 120 characters could fit on that same 8-inch line. CPL is also widely known as character pitch. CPS means characters per second. It is also related to moving-carriage printer designs and indicates just how fast your printer will generate complete characters. This specification is closely related to character pitch, so you will probably find one entry for each pitch setting. Smaller characters that are composed of fewer dots can be produced faster, so they will have a higher CPS rate. Larger characters (or letter-quality characters) are composed of more dots, so their CPS rate will be lower. Print direction is related to moving-carriage printers, and defines the way in which a printer's carriage can move during operation. Virtually all moving-carriage printers that produce simple text operate in a bidirectional mode as shown in figure 1-2. The carriage moves in one direction across a page, paper advances, then the carriage moves across the page in the opposite direction. Paper advances, then the carriage moves in its original direction again. Unidirectional printing is often used for more calculation-intensive printing applications such as bit-map graphics. The carriage moves in one direction across the page (usually left to right), the page advances, and the carriage moves back to its starting point before printing a sIndividual dots placed on a page are defined by several different specifications depending on whether the printer is working in a text or graphics mode. Moving-carriage printers typically define a dot configuration, which indicates the physical size of each dot being placed on the page. Impact dot-matrix print heads frequently provide a dot configuration of X2111 (0.2 mm) in diameter. Ink jet print heads often sport much smaller dot sizes. The dot alignment details how many dots are placed (vertically and horizontally) to form a character. For example, an impact printer dot alignment of 24 x 9 shows that a draft mode character is composed of up to 24 vertical dots, and 9 horizontal dots. In letter quality mode (LQ), this increases to 24 x 30. On the other hand, an ink jet printer in draft mode runs at 50 x 15, where LQ mode offers 50 x 30. This is why many ink jet printers provide better-looking text even in draft mode. Finally, dot pitch indicates how precisely dots can be placed in the horizontal and vertical direction. A typical impact printer can achieve a dot pitch of Ytzo11 (0.21 mm) in the horizontal direction, and Ytso11 (0.14 mm) in the vertical direction. In other words, the impact printer can place 120 horizontal dots per inch (dpi) and 180 vertical dots per inch. This is the printer's graphic resolution. While some impact printers are capable of up to 360 x 360 dpi, this produces a tremendous amount of print head heat and mechanical work, which results very slow printing. From a practical perspective, impact printers work best at low resolution (60 x 60 dpi or so). Ink jet printers are also capable of very fine resolutions (up to 360 x 360 dpi), and they provide faster performance since the print head does not get hot. Still, the slow rate at which ink dots can be ejected limits printing speed at high resolutions. As you will see in later chapters, EP printers are not limited by such constraints, and resolutions are available from 75 x 75 dpi to 1,200 x1,200 dpi (and higher). The "standard, operating resolution for current, low-end, commercial EP printers is 300 x 300 dpi. In the printer world, the reference to resolution always indicates that impact or ink jet printer is working in the graphics mode (EP printers work only in a graphics mode). Where moving-carriage printers focus on specifications, such as characters per second and lines per inch to establish a printing rate, EP printers simply define their printing speed as pages per minute (ppm). This rate is largely determined by the printer's mechanical design. Low-cost, low-end EP printers will work at 4 ppm, while high-cost, high-end EP models can operate at 12 ppm or higher. Keep in mind that ppm is an optimum printing rate-large graphic images might require additional time to transfer the corresponding data, which easily can slow printing. Warm-up time is another specification applied to EP printers. Impact and ink jet dot-matrix printers do not require warm-up time; they're ready to go as soon as you turn the printer on. However, EP printers must melt toner to the paper. This requires the EP printer to reach a stable working temperature. When the printer is operating correctly, a working temperature can be reached in under 90 seconds.
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