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I have been trying to figure out why the IBM graphics printer has a higher dpi in quadruple density , than the Epson MX-80 since technically the IBM graphics printer is a rebranded version of the MX-80.

Both printers have the same dpi resolution for single density and double density graphics mode, but when it gets to quadruple density the dpi is different vertically. The MX-80 in quadruple density mode has a resolution of 240 x 144 dpi , while the IBM graphics printer is 240 x 216 dpi.

I am guessing if the IBM graphics printer can do 240 x 216 dpi , so probably can the MX-80. Maybe there isn't a difference in print quality when printing with those resolutions? I know the print head is 72 dpi vertically, and has to overlap the dots to get 144 dpi, to get 216 dpi I am guessing the dots have to overlap even more?

Someone on here probably knows a correct answer to why the quadruple density is different on these printers even if they are technically the same printer.

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    I'm a bit confused - the Epson MX printer manual (e.g. at bitsavers, bitsavers.org/pdf/epson/printer/MX_Printer_Manual_1982.pdf) quite clearly talks about "one-third dot vertical spacing" and setting line spacings in units of 216'ths of an inch.
    – Jon Custer
    Feb 22, 2023 at 19:45
  • So it was possible to do that, but that option may not have been implemented by specific printer drivers.
    – Jon Custer
    Feb 22, 2023 at 19:59
  • The Star Gemini 10x printer was mostly Epson-compatible, but used 1/144" vertical spacing. I don't recall any other Epson-style printers doing likewise. The Apple ImageWriter did, but I recall it was different in other ways.
    – supercat
    Feb 22, 2023 at 20:31
  • @JonCuster The driver included with windows , for the Epson MX-80 only has 240 x 144 as a option , even though the windows driver for the IBM graphics printer does have it as 240 x 216. Feb 22, 2023 at 21:29
  • Interesting - so it would seem that it is a driver issue. Why Epson decided to hobble their driver is odd (unless IBM still had enough clout to impact it?).
    – Jon Custer
    Feb 22, 2023 at 22:44

1 Answer 1

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If you look at page 43 (PDF page 49) of the original MX-80 manual under the ESC G command, it achieves bold characters by double printing with a 1/216 inch paper advance. So obviously the paper feed mechanism was capable of 216 positions per inch, but it seems the ability to use this capability was extremely limited.

The Graftrax extension added the ESC 3 command to set line spacing in 1/216 inch increments. It may have also exposed other ways to use the 1/216 capabilities but I can't find a good reference at the moment.

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    The other limitation of most MX-80 ESC-3 compatible 9 pin printers were that they could not fire the pins on 2 successive pixel columns. In practice this meant that only a 1/120th inch horizontal resolution. The first program I know that enabled true 1/240 x 1/216 was the German text system Signum! on the Atari ST. Printing in this maximal resolution was extremely long as it made 2x3 passes for 9 pixel rows (1 hour printing a LQ A4 on my Seikosha SP-80 f.ex.). Feb 27, 2023 at 13:32
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    Nearly all of the Epson-compatible printers I've seen have two speeds of horizontal motion, can address 120dpi at faster speed and 240dpi at slower speed, and are limited to striking dots in every other position. Some Panasonic models add a third speed for carriage motion without printing.
    – supercat
    Feb 27, 2023 at 14:31
  • @MarkRansom Not sure if anyone else has caught this yet, but your link for the original mx-80 manual goes to the wrong link? I would have edited it to fix it, if I would have known where a link to the original manual is online. Feb 27, 2023 at 23:56
  • @MichaelWeaser it worked for me when I posted it, and it just worked again. It's a very long PDF though, so maybe it just didn't finish loading for you. Feb 28, 2023 at 3:26
  • @MarkRansom Thats odd , for me the link goes to an microsoft office manual? Feb 28, 2023 at 4:46

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