neously generate multi-cop- ies-a key advantage of impact printers. "Daisy wheel" printers were the outcome of a major innovation in serial impact printer mechanisms. As shown in Fig. 4-4, the daisy Paper Paper drive Ribbon Print hammer Wheel drive Print wheel Carrier drive Fig. 4-4. Daisy wheel printer. 58 TELECOMMUNICATIONS wheel printer uses fully formed characters on the tips of flexible bars arranged in a daisy-wheel fashion. This print wheel rotates and stops in front of an electromagnetic actuator to select a character to print. The daisy wheel with its light weight and simple rotation enables the printer to operate at a burst speed as high as 70 cps. Due to the need of increasing the flexibility of electronic font and form generation, wire matrix printers have made rapid strides. Wire matrix print heads (as shown in Fig. 4-5) have individually activated print wires usually arranged in a vertical array or staggered arrays. As the print head moves across the page, the print wires form char- acters in matrix boxes. With proper electrical controls, the wire ma- trix printer is capable of all-points-addressable printing to print graphs or images in addition to character printing. It is also possible Paper drive Paper Print wires Eight wire printhead Platen Emitter pick-up Grating Cable Carrier drive Fig. 4-5. Wire matrix printer. TERMINAL TECHNOLOGY 59 to obtain multi-copies. The multi-copy capability and reliability have made matrix impact printers attractive. Even though the print-speed distinction between a serial and a line printer has become less distinct and overlapped, a line printer is his- torically considered as printing a line of characters at once. Figure 4-6 shows a band line printer with an array of fixed hammer banks. The printing is accomplished by a set of fully formed characters ar- ranged in a chain or band moving in front of the hammer at a high speed to be addressed by the hammers. The band printer is capable of high-speed printing. The speed lim- itation for good quality printing is a fun