adobe photoshop - How to achieve this dot-matrix-printed/pixelated effect?

The above image is a Windows 95 default background. I wanted to know how they achieved this effect and was wondering if it is possible in Photoshop or if I need a dot-matrix printer or maybe a graphic-design program from the 90's to replicate it.

Answer

Open a photograph in Photoshop

Do Image > Adjusments > Desaturate

Then Image > Mode > Indexed color, and use the settings shown below.

Note: Afterwards, you can switch back to other modes such as RGB for further editing, by using Image > Mode > RGB