Line printer
Encyclopedia
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...
in which one line of type is printed at a time. They are mostly associated with the early days of computing, but the technology is still in use. Print speeds of 600 to 1200 lines-per-minute (approximately 10 to 20 pages per minute) were common.
Designs
Five principal designs existed:- Drum printers
- Chain (train) printers
- Bar printers
- Comb printers
- Wheel printers
Drum printer
Voice coil
A voice coil is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it...
s mounted on the moving part of the hammer.
Often the character sequences are staggered around the drum, shifting with each column. This obviates the situation whereby all of the hammers fire simultaneously when printing a line that consists of the same character in all columns, such as a complete line of dashes ("----").
Lower-cost printers did not use a hammer for each column. Instead, a hammer was provided for every other column and the entire hammer bank was arranged to shift left and right, driven by another voice coil. For this style of printer, two complete revolutions of the character drum were required with one revolution being used to print all the "odd" columns and another revolution being used to print all of the "even" columns. But in this way, only half (plus one) the number of hammers, magnets, and the associated channels of drive electronics were required.
At least one low-cost printer, made by CDC
Control Data Corporation
Control Data Corporation was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc....
, achieved the same end by moving the paper laterally while keeping the hammer bank at rest.
Dataproducts
Dataproducts
Dataproducts Corporation was an early manufacturer of computer peripheral equipment.Initially known as Data Products, the company was founded by Erwin Tomash in 1962 in order to take controlling interest of Telex's Data Systems Division. The division was behind on a contract to deliver disk files...
was a typical vendor of drum printers, often selling similar models with both a full set of hammers (and delivering, for example 600 lines-per-minute of output) and a half set of hammers (delivering 300 LPM).
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. A further advantage was that vertical registration of characters in a line was much improved over drum printers, which needed extremely precise hammer timing to achieve a reasonably straight line of print. 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 analysisFrequency analysis
In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers....
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
IBM 1403
The IBM 1403 line printer was introduced as part of the IBM 1401 computer in 1959 and had an especially long life in the IBM product line. The original model could print 600 lines of text per minute and could skip blank lines at up to 75 inches/second. The standard model had 120 print...
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. DataproductsDataproducts
Dataproducts Corporation was an early manufacturer of computer peripheral equipment.Initially known as Data Products, the company was founded by Erwin Tomash in 1962 in order to take controlling interest of Telex's Data Systems Division. The division was behind on a contract to deliver disk files...
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.
Comb printer
Comb printers, also called line matrix printerLine matrix printer
A line matrix printer is a computer printer that is a compromise between a line printer and a dot matrix printer. Basically, it prints a page-wide line of dots. It builds up a line of text by printing lines of dots.-Applications:...
s, represent the fourth major design. These printers were a hybrid of dot matrix
Dot matrix
A dot matrix is a 2-dimensional array of LED used to represent characters, symbols and images.Typically the dot matrix is used in older computer printers and many digital display devices. In printers, the dots are usually the darkened areas of the paper...
printing and line printing. In these printers, a comb of hammers printed a portion of a row of pixels at one time (for example, every eighth pixel). By shifting the comb back and forth slightly, the entire pixel row could be printed (continuing the example, in eight cycles). The paper then advanced and the next pixel row was printed. Because far less printhead motion was involved than in a conventional dot matrix printer, these printers were much faster than dot matrix printers and were competitive in speed with formed-character line printers while also being able to print dot-matrix graphics as well as variable-sized characters.
Printronix
Printronix
Printronix is an independent supplier of line matrix, Thermal Bar Code printer, radio frequency identification and mobility solutions. Printronix printers are typically used for bar code labeling of products, as well as high-volume printing of reports...
and TallyGenicom
TallyGenicom
The TallyGenicom brand, acquired by Printronix in 2009, includes laser and line matrix printers, parts, consumables and service. Printronix now owns the intellectual property and worldwide sales distribution rights for TallyGenicom line matrix and laser technologies, including printers, supplies...
are well-known vendors of comb printers.
Because all of these printing methods were noisy, lineprinters of all designs were enclosed in sound-absorbing cases of varying sophistication.
Wheel printers
In 1949, IBM introduced the IBM 407IBM 407
The IBM 407 Accounting Machine, introduced in 1949, was one of a long line of IBM tabulating machines dating back to the days of Herman Hollerith. It was the central component of any unit record equipment shop. In the late 1950s, the 407 was adapted as an input/output device on early computers,...
Accounting Machine with a wheel print mechanism that could 150 alphanumeric lines a minute. Each of the 120 print positions had its own type wheel which rotated under electromechanical control. Once all were in position, print hammers struck the wheels against a ribbon and the paper. The 407 or its wheel line printer mechanism was attached to a variety of early IBM computer, including the IBM 650
IBM 650
The IBM 650 was one of IBM’s early computers, and the world’s first mass-produced computer. It was announced in 1953, and over 2000 systems were produced between the first shipment in 1954 and its final manufacture in 1962...
, most members of the IBM 700/7000 series
IBM 700/7000 series
The IBM 700/7000 series was a series of large-scale computer systems made by IBM through the 1950s and early 1960s. The series included several different, incompatible processor architectures. The 700s used vacuum tube logic and were made obsolete by the introduction of the transistorized 7000s...
and the IBM 1130
IBM 1130
The IBM 1130 Computing System was introduced in 1965. It was IBM's least-expensive computer to date, and was aimed at price-sensitive, computing-intensive technical markets like education and engineering. It succeeded the IBM 1620 in that market segment. The IBM 1800 was a process control variant...
, the last introduced in 1965.
Paper (forms) handling
All line printers used paperPaper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
provided in boxes of continuous fan-fold forms rather than cut-sheets. The paper was usually perforated
Perforation
A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes are called a perforation...
to tear into cut sheets if desired and was commonly printed with alternating white and light-green areas, allowing the reader to easily follow a line of text across the page. This was the iconic "green bar" form that dominated the early computer age. Pre-printed forms were also commonly used (for printing cheque
Cheque
A cheque is a document/instrument See the negotiable cow—itself a fictional story—for discussions of cheques written on unusual surfaces. that orders a payment of money from a bank account...
s, invoice
Invoice
An invoice or bill is a commercial document issued by a seller to the buyer, indicating the products, quantities, and agreed prices for products or services the seller has provided the buyer. An invoice indicates the buyer must pay the seller, according to the payment terms...
s, etc.). A common task for the system operator was to change from one paper form to another as one print job completed and another was to begin. Some lineprinters had covers that opened automatically when the printer required attention.
Standard "green bar" page sizes included portrait-format pages of 8½ × 11 inches, usually printed at 80 columns by 66 lines (at 6 lines per inch
Lines per inch
Lines per inch is a measurement of printing resolution in systems that use a halftone screen. Specifically, it is a measure of how close together the lines in a halftone grid are. Higher LPI indicates greater detail and sharpness....
) or 88 lines (at 8 LPI), and landscape-format
Landscape format
Landscape format is a format of printed material of which the width of the article is larger than the height. This is the opposite of Portrait format...
pages of 14 × 11 inches, usually printed at 132 columns by 66 or 88 lines. Also common were landscape-format pages of 14 × 8½ inches, allowing for 132 columns by 66 lines (at 8 LPI) on a more compact page.
These continuous forms were advanced through the printer by means of tractors (sprocket
Sprocket
A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which are radial projections that engage a chain passing over it...
s or sprocket belts). Depending on the sophistication of the printer, there might simply be two tractors at the top of the printer (pulling the paper) or tractors at the top and bottom (thereby maintaining paper tension within the printer). The horizontal position of the tractors was usually adjustable to accommodate different forms. The earliest printers by IBM used a hydraulic motor to move the forms. In later line printers, High-speed servomechanism
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
s usually drove the tractors, allowing very rapid positioning of the paper, both for advancing line-by-line and slewing to the top of the next form. The faster line printers, of necessity, also used "stackers" to re-fold and stack the fan-fold forms as they emerged from the printer.
The high-speed motion of the paper often developed large electrostatic
Electrostatics
Electrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....
charges. Line printers frequently used a variety of discharge brush
Brush
A brush is a tool with bristles, wire or other filaments, used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools known to mankind, and the average household may contain several dozen varieties...
es and active (corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
-based) static eliminators to discharge these accumulated charges.
Many printers supported ASA carriage control characters
ASA carriage control characters
ASA control characters are simple printing command characters used by mainframe printers to control the movement of paper through line printers. These commands are presented as special characters in the first column of each text line to be printed, and affect how the paper is advanced before the...
which provided a limited degree of control over the paper, by specifying how far to advance the paper between printed lines. Various means of providing vertical tabulation were provided, ranging from a paper carriage control tape
Carriage control tape
A carriage control tape was a loop of punched tape that was used to synchronize rapid vertical page movement in most IBM line printers from unit record days through the 1970s. The tape loop was as long as the length of a single page. A pin wheel moved the tape accurately using holes in the center...
loop to fully electronic (software-controllable) tab simulation.
Origins
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, introduced the first tabulating machine
Tabulating machine
The tabulating machine was an electrical device designed to assist in summarizing information and, later, accounting. Invented by Herman Hollerith, the machine was developed to help process data for the 1890 U.S. Census...
with a printer in 1920. Prior to that, tabulator operators had to write down totals from counter wheels onto tally sheets. IBM developed a series of accounting machines over the next four decades with improved printing capabilities. The 285 Numeric Printing Tabulator could read 150 cards per minute. The 405, introduced in 1934, could print at 80 lines per minute. It had 88 type bars, one for each print position, with 43 alphanumeric bars on the left, followed by 45 numeric-only bars. The IBM 402
IBM 402
The IBM 402 and IBM 403 Accounting Machines were tabulating machines introduced by IBM in the late 1940s. The 402 could read punched cards at a speed of up to 150 cards per minute, while printing data at a speed of up to 100 lines per minute with 43 alpha-numerical type bars and 45 numerical type...
series, introduced after World War II, had a similar print arrangement and was used by IBM in early computing devices, including the IBM Card-Programmed Electronic Calculator
IBM CPC
The IBM Card-Programmed Electronic Calculator or CPC was announced by IBM in May 1949. Later that year an improved machine, the CPC-II was also announced.The original CPC Calculator had the following machines interconnected by cables:...
.
An early drum printer was the "Potter Flying Typewriter", in 1952. "Instead of working laboriously, one character at a time, it prints whole lines at once, 300 lines per minute, on a paper band. ... Heart of the machine is a continuously spinning disk with the necessary letters and numbers on its rim. ... As the disk revolves, 80 electrically operated hammers tap the back of the paper against an inked ribbon in contact with the disk, thus printing the proper characters in the proper places on the line."
Current applications
While the limited character set, fixed character spacing, and relatively poor print quality make impact line printers unsuitable for correspondence, books, and other applications requiring high print quality, the technology is cost-effective and remains in limited use in a number of applications such as printing box labels, medium volume accounting and other large business applications.The names of the
lpLp (Unix)The lp command is used on many Unix-like systems to assign jobs to printer queues. The name derives from "lineprinter", though it has become the commonly used command for any sort of printer...
and lprLine Printer Daemon protocolThe Line Printer Daemon protocol/Line Printer Remote protocol is a network protocol for submitting print jobs to a remote printer. The original implementation of LPD was in the Berkeley printing system in the BSD UNIX operating system; the LPRng project also supports that protocol...
commands in UnixUnix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
were derived from the term "line printer". Analogously, many other systems call their printing devices "LP", "LPT", or some similar variant, whether these devices are in fact line printers or other types of printers. These references served to distinguish formatted final output from normal interactive output from the system, which in many cases in line printer days was also printed on paper (as by a teletype) but not by a line printer.
See also
- TypewriterTypewriterA typewriter is a mechanical or electromechanical device with keys that, when pressed, cause characters to be printed on a medium, usually paper. Typically one character is printed per keypress, and the machine prints the characters by making ink impressions of type elements similar to the pieces...
- ASA carriage control charactersASA carriage control charactersASA control characters are simple printing command characters used by mainframe printers to control the movement of paper through line printers. These commands are presented as special characters in the first column of each text line to be printed, and affect how the paper is advanced before the...
- Characters per lineCharacters per lineIn typography and computing characters per line or terminal width refers to the maximal number of monospaced characters that may appear on a single line...
- Line matrix printerLine matrix printerA line matrix printer is a computer printer that is a compromise between a line printer and a dot matrix printer. Basically, it prints a page-wide line of dots. It builds up a line of text by printing lines of dots.-Applications:...
- lp0 on fireLp0 on firelp0 on fire is a semi-obsolete error message still generated on some Unix and Unix-like operating systems in response to certain types of printer errors...