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Ballistic Wire PrinterIn a ballistic wire computer printer, a print head has holes drilled through it. Thin wires go through the print head. Pawls are actuated by solenoids. The pawls strike the wires, causing them to go out and hit an inked ribbon, which hits the paper. This form of printer was common for home and office use in the 1980s, but they are noisier and more expensive to produce than ink-jet printers. When Hewlett-Packard's patents expired on the steam-propelled photolithographically-produced ink-jet heads, ink-jets were universally adopted for home printers, despite their higher costs of ownership. The chief advantage of wire-channel impact printers is a low cost of ownership. Unlike ink-jet printers, replacing the ink-source is usually only a few dollars, like replacing a typewriter ribbon. They are still used where carbon copies are necessary, and because of their low cost of ownership they are commonly used in cash registers to print receipts. The print resolution ranges from 50 to 300 dots per inch (500 to 85 micrometres). The poorer resolution is used for receipt printers. The finer resolution is used on premium graphic printers because the dots are invisible to the human eye at 14 inches (350 mm). The way the mechanism wears is that ink invades the block. Grit adheres to the ink and slowly causes the channels in the head to wear to ovals or slots. The channels become loose. After about a million characters, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read. See also: Dot matrix printer
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