MALCOLM L. STIEFEL, President • M. L. Stiefel Co.
INTRODUCTION
This Profile series places the spotlight on printers for the first time since 1968.1 Long past their barely legible, wavy-lined infancy, but far from reaching their dotage, printers are changing dra-matically-they're getting faster, cheaper, and quieter; they're being used in new varieties of sys-tem configurations; and the outputs are starting to provide quality copies.
Part I of this series will deal with medium- and high-speed line printers (or page printers). A line printer is arbitrarily defined to be one without keyboard that is driven by an external digital source (computer, communications line, magnetic tape, etc.) to print rows (lines) of alphanumelic data on paper, at no less than 80 columns per line and at a maximum speed of not less than 100 lines per minute. This maximum rate excludes anything that trudges along at less than 120 characters per second and omits virtually all of the one-character-at-a-time printers, which will be treated in Part II of this series next month. Interactive printers with keyboards, called telewriters or teleprinters, will be treated in another Technology Profile.
TYPES OF PRINTERS
Quickly now, without peeking, picture a high-speed line printer in your mind. It looks like the one in Fig. 1, right? 1200 lines a minute; pin-fed, fan-folded paper with green and white horizontal stripes and little holes running up and down the sides. Well, that's called an impact printer, and it prints much like a conventional typewriter. An
im-1 J. H. Levine, "High-Speed Line Printe1's," MODERN DATA;
May, 1968
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pression is transferred from a type slug on a drum, chain, or wheel to the paper. Ink is provided by a ribbon or a roller, or is incorporated in the paper itself. Multiple copies may be obtained since the character impact - as in a typewriter - can be transmitted through the first or original copy to other sheets in a multi-part form. Another class of impact printers uses a solenoid-driven matrix of points to form a dot matrix character on the paper;
they also have multi-copy capabilities.
Then there are the non-impact varieties of print-ers. These include the shpl'itzer types - printers that spray controlled jets of ink onto the page to form the characters. There are also the elec-trostatic or electrographic non-impact types -printers that use electrodes or other image matrix mechanisms to construct characters on sensitized paper. Another type of non-impact printer utilizes electro-optics to flash an optical image on photo-graphic paper or film to form the character. All of these types are silent - as opposed to the clatter-ing impact varieties - but they can only provide one copy per print run.
OPTIONS UNLIMITED
Today users are almost overwhelmed by printer options. Speeds can vary from 100 to 5000 lines per minute. Some units have a 50 character font; others carry up to 432 symbols at a time. Some may print at fixed densities of 10 characters per inch horizontally, while others vary horizontal density. Most print at operator-selectable vertical line densities of 6 or 8 lines to the inch, with ver-tical formatting either done with software and a carriage control tape, or by software alone.
In one common approach, vertical positioning commands on the input line are limited to "Skip One Line" and "Skip To Top Of Next Page." An-other option offers "Skip n Lines" and "Skip To
MODERN DATA/February 1971
Next Vertical Tab Stop." The option selected can make a considerable difference in printing time for many types of forms; a "Skip To Top Of Next Page" or "Next Tab Stop" is generally accom-plished much faster than a "Skip One Line" or "Skip n Lines" at a time. In one specific case there isn't any vertical control. The printer just runs at a con-stant speed. The user is responsible for feeding it data; otherwise it degenerates into a large-volume paper towel dispenser.
There are more choices of symbol fonts than you can shake a stick at. Some printers require major surgery to change a font; some can't be changed at all; on others, it's a matter of plugging in a cartridge. In the case of the phototypesetting models, several fonts are available on-line. More-over, some may be printer/plotters, offering both graphic capability and line printing.
The choices go on and on: 80 to 160 columns of print; page sizes up to 2 feet wide and 2 feet long;
fan-folded paper or paper in rolls, perforated or non-perforated; specially treated paper - heat sensitive, light sensitive, pressure sensitive; carbon copies and carbonIess copies; and some printers with no duplicate copies at all.
A user with a large computer and a high print-out volume could turn to the satellite con-figuration concept. A print image is recorded on magnetic tape or disk packs on-line, at fairly high speeds. Then the tape or disk pack is physically removed and placed on another device in a sepa-rate, cheaper, completely compatible off-line print-ing system. This technique, termed off-line print-ing or satellite printprint-ing is likely to spread in the future. It will mature into a complete class of sys-tems which involve all kinds of computer per-ipherals connected together to transfer and trans-form information without substantially alteri~g its sequence and content. By strictly limiting process-ing to parity checking and some elementary logi-cal operations, programming is minimized or avoided entirely, equipment is made simple and reliable, and a few bucks can be saved in overall system operation.
MODERN DATA/February 1971
PICKING A PRINTER
This bewildering array of options becomes more manageable to a user who is trying to pick a printer for his own needs. For instance, if the printer is to be used in a medium-scale data proc-essing operation, the user is likely to turn to the mainframe manufacturer or to someone else who offers a direct replacement for the manufacturer's printer. For this situation the analysis has been done beforehand; the user is sure to wind up with a printer that is well matched in price, speed, and flexibility to the remainder of his data processing system.
For other users, the picture is quite different.
The appearance, legibility, and print density be-come important if the output is to be published and widely disseminated. This leads to an exam-ination of phototypesetting machines, or to a printer that uses an attractive type font with up-per and lower case letters.
Virtually any printer maker can supply custom-tailored fonts for customers, at an extra cost. The limitation is in the number of characters in the symbol set, and in the effect of a given font on speed...:.... since printer speed varies inversely (in a non-linear manner) with the size of the font used.
Printer speed is also affected (in impact printers) by the relationship between the layout of the sym-bols around the drum or chain and the frequency of occurrence of each character in the set of
sym-MR. STIEFel is an independent consultant based in Chelmsford, Mass. Since 1969, he has been engaged in the design, evaluation, and implementation of municipal information and inventory control systems, and has several free·
lance articles dealing with computer applica-tions to his credit. His background includes over 10 years in analysis, design, testing, and evaluation of hospital information systems and military command and control systems. He received his B.S.E.E. from the Polytechnic Institute of Brooklyn in 1959 and has completed graduate work at M.I.T.
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TECHNOLOGY PROFILE: PRINTERS ., ... Cont'd
Fig. I-The Univac 0758-00. a high-speed line printer capable of 1200 LPM with a 63-character drum.
Fig. 2-The Vogue Instrument. Shepard Division's Model 880E medium-speed line printer capable of 400 LPM using a drum of 64 characters.
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Fig. 3-The MP Series off-line magnetic-tape-to-print system of Per Data. featuring a 600 LPM printer and a 7/9 track tape drive.
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Fig. 4-The Gould 4800 high-speed electrostatic printer/plotter used in on- and off-line printing systems.
Fig. 5-The Centronics 101 impact matrix medium-speed printer. capable of up to 150 LPM rates.
Fig. S-Odec Computer System Model 801. a 150 LPM. 80-column chain printer with RS 232 interface.
MODERN DATA/February 1971