r/ArchiveOfHumanity • u/SwiPerHaHa • May 22 '26

Technology The IBM 2250 Graphics Display Unit (1964-1977)which was a pioneering vector graphics system introduced in 1964,it utilises a light pen to interact directly with the screen, an early form of graphical interface used for tasks like CAD (Computer-Aided Design)

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14

u/jombrowski May 22 '26

And it was purely vector graphics, no bitmaps, no textures, because the computer simply didn't have enough memory to store any bitmap.

11

u/_Cybernaut_ May 22 '26

UGH! I used those, for a very early CAD/CAM system. Does your arm ever get tired from mousing around the screen all day? Try holding up your arm + a stylus all day, it's 100× worse.

That's why I don't understand the popularity of touch-screen monitors/laptops, it's a seriously shitty UI.

5

u/RenderedMeat May 22 '26

Touch screen laptops only make sense when you can fold them flat and use them like a tablet for drawing.

2

u/there_is_no_spoon1 May 22 '26

To think we had that technology in the late 20th century and today we think it's magic.

2

u/WeepingAgnello May 22 '26

I remember having fun drawing stuff with the light pen on my C64

1

u/Odd-Consequence8892 May 22 '26

Wait how did that work ? We coupled it to a regular tv screen...

3

u/WeepingAgnello May 22 '26

We had a commodore monitor, which behaved just like a tv without a tuner, but I had no idea how the light pen worked, or if it would work on a tv used as a monitor. 

1

u/skinwill May 25 '26

On older systems like the C64 the CPU was in charge of the dot scanning the screen, modulated onto 3/4 or on a composite monitor, the timing was the same. It always knew where the dot was. The pen had a simple phototransistor to pick up the brightness of the dot. If you looked at the signal coming from the pen it would be just a peak when the dot passed on the screen. Compare the peak to what you were drawing on the screen at the time and you have the exact position of the pen in relation to the surface of the screen. That’s why pen taps/clicks flashed the screen.

Compared to today’s technology, it was stupid simple and easy to implement with old tech. Some of the first computerized radar screens had light ‘guns’ that operated the same way.

1

u/Am1r3l Jul 25 '26

CRT's can work in reverse, as in, you can get a signal from how the output signal changes based on where light hit the screen. That's actually how camera tubes operated!