Chain (train) printer

Chain (train) printer

Chain printers (also known as train printers) placed the type on moving bars (a horizontally-moving chain). As with the drum printer, as the correct character passed by each column, a hammer was fired from behind the paper. Compared to drum printers, chain printers had the advantage that the type chain could usually be changed by the operator. By selecting chains that had a smaller character set (for example, just numbers and a few punctuation marks), the printer could print much faster than if the chain contained the entire upper- and lower-case alphabet, numbers, and all special symbols. This was because, with many more instances of the numbers appearing in the chain, the time spent waiting for the correct character to "pass by" was greatly reduced. Common letters and symbols would appear more often on the chain, according to the frequency analysis of the likely input. It was also possible to play primitive tunes on these printers by timing the nonsense of the printout to the sequence on the chain, a rather primitive piano. IBM was probably the best-known chain printer manufacturer and the IBM 1403 is probably the most famous example of a chain printer.

Band printer

Band printers are a variation of chain printers, where a thin steel band is used instead of a chain, with the characters embossed on the band. Again, a selection of different bands were generally available with a different mix of characters so a character set best matched to the characters commonly printed could be chosen. Dataproducts was a well known manufacturer of band printers, with their B300, B600, and B1000 range, the model number representing the lines per minute rate of the printer. (The B300 was effectively a B600 with only half the number of hammers—one per two character positions. The hammer bank moved back and forth one character position, requiring two goes to print all characters on each line.)

Bar printer

Bar printers were similar to chain printers but were slower and less expensive. Rather than a chain moving continuously in one direction, the characters were on fingers mounted on a bar that moved left-to-right and then right-to-left in front of the paper. An example was the IBM 1443.In all three designs, timing of the hammers (the so called "flight time") was critical, and was adjustable as part of the servicing of the printer. For drum printers, incorrect timing of the hammer resulted in printed lines that wandered vertically, albeit with characters correctly aligned horizontally in their columns. For train and bar printers, incorrect timing of the hammers resulted in characters shifting horizontally, albeit on vertically-level printed lines.Most drum, chain, and bar printers were capable of printing up to 132 columns, but a few designs could only print 80 columns and some other designs as many as 160 columns.