system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did America have 60hz TVs while Europe had 50hz and why does it effect the speed old video games run at?
gpt
In America the electrical system uses Alternating Current set at a rate of 60hz. This means the current of electricity changes from positive to negative 60 times per second. In Europe, the rate is at 50 times per second, or 50 hz.  The first TVs worked by painting the screen with electrons in a left to right and top to bottom pattern, so it would draw a line of pixels horizontally, then it would step down and reset the brush, and paint the next line, similar to how you would type on a typewriter.

It also had to do this entirely in one polarity of the electrical system, so it had to do it 60 times per second in the US, because if it wasn't finished drawing the screen, the image would not be drawn correctly. To help this a technique called interlacing was created to draw only half of the screen during each cycle. So instead of drawing every line, it would draw every other line. This is all the same in Europe, except that because their electrical system switches polarity slower, they have more time available between refreshes, so their televisions run at 50hz like their electrical system.

These issues are mostly limited to Analog TVs, which are being phased out, as Digital TVs can access pixels independently, rather than having to redraw the entire screen to refresh anything.