Printer Evolution

[Received via e-mail: March 31, 1997]

When I first started working on computer systems, the main form of output was the high-speed printer. These were monsters, weighing between 1000 and 2000 lbs., depending on the speed and technology. The early printers had bars of print for each column, and each bar had all the characters. There was a complex mechanism to raise each bar to the desired letter and then a hammer would hit all the letters at once for one row. Then you hoped that the hammers would get out of the way before the bars went down again. These were very large, very noisy, and prone to break down.

When I started, the printers with bars were at the end of their life and I only saw one or two in use. The ones I worked on were the new style, with letters that did not stop in motion as the bars did. The timing of the print hammer had to be just right, so that it would hit the correct letter as it flew past the position that you wanted printed. This was called printing on the fly.

There were two main types of these newer printers: the letters went by in either a vertical direction or in a horizontal direction. If they went by in a vertical direction, then you sometimes got wavy lines; if they went by in a horizontal direction, then you got extra spaces between the letters, or they were crowded up. You could adjust most of these problems out if you had lots of time.

The first type of printer was called a drum printer, because it had a drum with all the characters for each print position, either 120 or 132 print positions. If you looked at the drum you could see that there was a whole row of As followed by a row of Bs and so on. The other type of printer was called either a chain or train printer, depending on whether the characters were pulled or pushed passed the print positions.

One day I went to one of the main computer sites in London and found one of my colleagues working on one of the large drum printers. He was trying to adjust something behind the print drum, but as he wasn't very tall he had to lie on top of the printer right across the drum enclosure. I said to him, when I saw this, "This gives a new meaning to printing on the fly!"