Billions of documents have been sent to printers around the world from the first PC to the most advanced, but printers communicate with the PC in a certain way, which we will explain below.
PC and Printer communication in the early days of the PC
The first PC video card was the MDA or Monochrome Display Adapter, which was intended for IBM 80-column monochrome monitors that did not follow the NTSC standard. Well, next to the video output of said graphics card was the output of the printer.
It was only necessary to press the Print Screen key so that what was seen on the screen at that moment was sent through the printer port so that it would be reflected on the printing paper. So in the early days of the PC, document printing was based only on printing what was seen on the screen, which was mostly monochrome text without any images.
Over time, the capabilities of computers grew and allowed the manipulation not only of text but also of images.
The layout boom of the mid-1980s
Looking back, Apple’s Macintosh was a huge commercial failure, but it managed to find a niche in the prepress and editorial layout market thanks to Aldus Pagemaker software and Apple’s LaserWriter printer. The combination of these two elements made it possible to layout pages with text and images at the same time and print them on paper documents without having to pull complex cut-out collages as was done until then.
All this was possible thanks to the PostScript support of the Apple printer, which allowed the printer to recreate complex pages with different fonts, font sizes and even draw both drawings and images on paper. Little by little the different computers of the time, including the PC, were adopting PostScript technology that allowed communication between the computer and the printer and created the PC ↔ Printer communication standard that continues to be maintained today.
The PostScript language for communication between PC and printer
PostScript is what we call a page description language, this language is used by programs to describe how the page is to the printer. As it defines to the printer what to print, how to print it and where to print it. When a PC sends data to a printer, what it does is send it information in PostScript format that the printer knows how to interpret.
Printers also have large ROMS inside them, nowadays eMMC memory is used in some models, which include entire collections of typefaces in different sizes. When we install a new font on our PC, its information is sent to the printer in all its sizes, in such a way that when a document is printed with that font, the printer searches its internal memory.
All the programs that need to print what they do is create a PostScript file, which is sent by the communication interface between the PC and the printer. Either by cable or through a wireless interface.
What is the PostScript language like?
For the manipulation of text PostScript has instructions such as the following:
- Findfont font type: We indicate the name of the new font type so that the printer looks for it in its memory and uses it from that point on.
- n scalefont: where n is the size of the font’s diagonal in pixels.
On the other hand, when drawing complex shapes, it indicates how they should be drawn. For this we have the following instructions:
- newpath: Indicates the beginning of a new line.
- x, y moveto: x and y are the coordinates on the page, moveto is to move the cursor to those coordinates.
- n setlinewidth: it is used to set the width in pixels of the line to be drawn
- setcolor: allows us to change the color used.
- n rotate: Where n is the number of degrees to rotate the object clockwise.
The PostScript language is therefore a language in which it is defined as a page is made. This is so due to the fact that sending the complete page through the bus that communicates the PC with the printer would be too slow.
That is why what is done is to send the data in PostScript format from the PC so that the printer itself can interpret it internally and compose the page internally and then print it, which means that within each printer there is really a computer.
Nowadays, high-capacity printers usually have entire pages in their memory that they have already printed, which is why when police raids for tax fraud are carried out, not only computers but also printers are taken.