Changes

===Solid print heads===

===Solid print heads===

The original printers used a metal cylinder with the character glyphs embossed on the surface. The cylinder was rotated and raised/lowered so that the appropriate glyph faced the paper.  The head was then forced forward against an inked ribbon and then the paper, forming the image on the paper in ink.

The original printers used a metal cylinder with the character glyphs embossed on the surface. The cylinder was rotated and raised/lowered so that the appropriate glyph faced the paper.  The head was then forced forward against an inked ribbon and then the paper, forming the image on the paper in ink.  The head was moved left to right with the process repeated for each column.  When the head reached the right side, it returned to the left side to begin the next line.

Line printers also used metal cylinders (called "drums"), except that the cylinders were oriented horizontally with up to 132 stripes the circumscribed the drum - one for each column.  Each stripe had all printable glyphs, so that if you looked at the drum while rotating it, you would see a line of 132 "A"s across the width, then a line of 132 "B"s, and so forth.  The printer spun the drum at high speed and when the appropriate letter for a given column has spun into position, a hammer behind the paper would quickly push the paper into contact with the embossed glyph on the drum, with an inked ribbon between them, thus placing the character onto the paper.  Since more than one instance of a given character would often occur on the same line, multiple hammers would strike the paper at the same time (for each column that used that character on that line), thus an entire line of text could be transferred to the paper during a single rotation of the drum.

Line printers also used metal cylinders (called "drums"), except that the cylinders were oriented horizontally with up to 132 stripes that circumscribed the drum - one for each column.  Each stripe had all printable glyphs, so that if you looked at the drum while rotating it, you would see a line of 132 "A"s across the width, then a line of 132 "B"s, and so forth.  The printer spun the drum at high speed and when the appropriate letter for a given column has spun into position, a hammer behind the paper would quickly push the paper into contact with the embossed glyph on the drum, with an inked ribbon between them, thus placing the character onto the paper.  Since more than one instance of a given character would often occur on the same line, multiple hammers would strike the paper at the same time (for each column that used that character on that line), thus an entire line of text could be transferred to the paper during a single rotation of the drum.

Band printers used a similar approach except that the glyphs were embossed on a belt that spun in a horizontal direction.  The belt had only a single instance of each character, but as the belt traveled across the paper, hammers would strike when the appropriate character was in the appropriate position - often with many hammers striking simultaneously when the appropriate glyphs lined up with the appropriate column.

Band printers used a similar approach except that the glyphs were embossed on a belt that spun in a horizontal direction.  The belt had only a single instance of each character, but as the belt traveled across the paper, hammers would strike when the appropriate character was in the appropriate position - often with many hammers striking simultaneously when the appropriate glyphs lined up with the appropriate column.