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Those old IBM line printers... how were they so fast and (relatively) accurate? And why is my home printer so much slower? For example, the IBM 1403[0] Model 3

Those old IBM line printers... how were they so fast and (relatively) accurate? And why is my home printer so much slower? For example, the IBM 1403[0] Model 3 could supposedly do 1400 lines per minute(!) Even if I assume 100 lines per page, that's still 14 pages per minute. My home printer is lucky to do five. [0]: https://en.wikipedia.org/wiki/IBM_1403 https://en.wikipedia.org/wiki/IBM_1403

codemac 6y ago
$$$$$$$$$ Also the wikipedia link you pasted itself has a section on technology, and specifically how it was so much faster (pushed the paper into the ink rather than the ink into the paper).
kens 6y ago
I've done a lot with the classic IBM 1403 line printer. The basic idea is that a rotating chain has the characters on it and zips around at 90.3 inches per second. The printer has 132 hammers, one for each column on the page. When the right character lines up with a hammer, the hammer fires, printing the character. This lets the printer output a full line in 80 milliseconds. The details of the print chain process are much more complex than you'd expect (so feel free to skip this paragraph). The computer has to constantly check to see when a hammer should fire. One important thing is that only one hammer lines up with a character at a time. (It's physically impossible to fire all the hammers at once.) During this time, the computer reads the corresponding character from memory and fires the hammer if it matches. To make this work, the chain/hammer timing has to match the core memory cycle timing. The chain spacing is very slightly different from the hammer spacing, so you end up with a vernier effect where the aligned character position changes much faster than the chain actually moves. I made an animation that might make things clearer: http://righto.com/ibm1401/printchain.html http://righto.com/ibm1401/printchain.html Another thing that makes the printer fast is it has a hydraulic motor to advance the paper very quickly. Inconveniently, the printer at the Computer History Museum is leaking hydraulic fluid, so we need to mop it up regularly. (That's one advantage of your home printer.) The print quality of the 1403 line printer was much better than competitors because it used a chain instead of typebars or a drum. In particular, if the timing was a bit off, the chain caused the character to be shifted left or right. Other approaches caused the character to be shifted up or down. A left-right shift is barely noticeable, while an up-down shift makes the text look wavy and awful. By the way, a laser printer (e.g. Brother) is a good choice for a home printer if you want more speed and don't like the expense of ink.
- parsecs 6y ago
  That animation is very, very informative. Thank you for your blogs and stuff like this!
- winrid 6y ago
  I love the breadth of knowledge on this site. Thank you for this in depth explanation.
Johnny555 6y ago
It's not that hard to find a fast printer if print speed is important to you. I have a Brother MFCJ6535DW inkjet printer that's rated at 35 ppm black and white and 22 ppm color. I haven't measured it precisely, but it's doing at least 20 pages per minute. I think when it was new it cost around $500, but I got this one as a refurb for $180. (my wife works in a state regulated industry and prints a lot of paper - 500 - 1500 pages/month, so the printer gets a workout, and consumables are cheap - a 3000 page black ink cartridge costs around $25, about half the price as toner for our old laser printer and has no other consumables to replace like a fuser drum)
eMGm4D0zgUAVXc7 6y ago
Here's a fun IBM line printing video I've discovered thanks to your mention of those: The IBM 1401 mainframe runs "Edith" https://www.youtube.com/watch?v=LtlrITxB5qg https://www.youtube.com/watch?v=LtlrITxB5qg
m463 6y ago
I share your amazement. The thing was - they did everything mechanically. They were like chainsaws with accurate solenoids, in small soundproof booths.

codemac 6y ago

$$$$$$$$$ Also the wikipedia link you pasted itself has a section on technology, and specifically how it was so much faster (pushed the paper into the ink rather than the ink into the paper).

kens 6y ago

I've done a lot with the classic IBM 1403 line printer. The basic idea is that a rotating chain has the characters on it and zips around at 90.3 inches per second. The printer has 132 hammers, one for each column on the page. When the right character lines up with a hammer, the hammer fires, printing the character. This lets the printer output a full line in 80 milliseconds. The details of the print chain process are much more complex than you'd expect (so feel free to skip this paragraph). The computer has to constantly check to see when a hammer should fire. One important thing is that only one hammer lines up with a character at a time. (It's physically impossible to fire all the hammers at once.) During this time, the computer reads the corresponding character from memory and fires the hammer if it matches. To make this work, the chain/hammer timing has to match the core memory cycle timing. The chain spacing is very slightly different from the hammer spacing, so you end up with a vernier effect where the aligned character position changes much faster than the chain actually moves. I made an animation that might make things clearer: http://righto.com/ibm1401/printchain.html http://righto.com/ibm1401/printchain.html Another thing that makes the printer fast is it has a hydraulic motor to advance the paper very quickly. Inconveniently, the printer at the Computer History Museum is leaking hydraulic fluid, so we need to mop it up regularly. (That's one advantage of your home printer.) The print quality of the 1403 line printer was much better than competitors because it used a chain instead of typebars or a drum. In particular, if the timing was a bit off, the chain caused the character to be shifted left or right. Other approaches caused the character to be shifted up or down. A left-right shift is barely noticeable, while an up-down shift makes the text look wavy and awful. By the way, a laser printer (e.g. Brother) is a good choice for a home printer if you want more speed and don't like the expense of ink.

parsecs 6y ago
That animation is very, very informative. Thank you for your blogs and stuff like this!
winrid 6y ago
I love the breadth of knowledge on this site. Thank you for this in depth explanation.

Johnny555 6y ago

It's not that hard to find a fast printer if print speed is important to you. I have a Brother MFCJ6535DW inkjet printer that's rated at 35 ppm black and white and 22 ppm color. I haven't measured it precisely, but it's doing at least 20 pages per minute. I think when it was new it cost around $500, but I got this one as a refurb for $180. (my wife works in a state regulated industry and prints a lot of paper - 500 - 1500 pages/month, so the printer gets a workout, and consumables are cheap - a 3000 page black ink cartridge costs around $25, about half the price as toner for our old laser printer and has no other consumables to replace like a fuser drum)

eMGm4D0zgUAVXc7 6y ago

Here's a fun IBM line printing video I've discovered thanks to your mention of those: The IBM 1401 mainframe runs "Edith" https://www.youtube.com/watch?v=LtlrITxB5qg https://www.youtube.com/watch?v=LtlrITxB5qg

m463 6y ago

I share your amazement. The thing was - they did everything mechanically. They were like chainsaws with accurate solenoids, in small soundproof booths.