To put it briefly, 4th generation and earlier games consoles saved on expensive RAM by not having frame buffers [0]. The CPU wrote a description of how to construct the scene using tiles and sprites to a smaller video ram, then dedicated video hardware converted this to the video signal one line at a time. The whole frame gets rendered from scratch every video refresh, so there's no need for tricks like Commander Keen's adaptive tile refresh. Scrolling at 60 fps (or 50 fps for PAL hardware) is as cheap as changing a single value in video memory. It's like the famous "racing the beam" of the Atari 2600, except less flexible and done by dedicated hardware so you don't tie up the CPU.
On the PC, the CPU writes the actual graphics to a frame buffer, then the graphics card outputs the contents of the frame buffer as the video signal. The naive approach to scrolling requires rewriting the entire frame buffer, so tricks to avoid redundant writes are highly beneficial.
[0] Except for the Atari Lynx, which was a portable system with a screen resolution of only 160×102. I can't think of any other exceptions, but maybe there are more.
That's the same as the Atari 2600. It just occurred to me that the name "racing the beam" is misleading because you can't be too fast either. "Matching the beam" would be a better name. My point is the graphics hardware in both the 2600 and in tile+sprite consoles assembles the graphics just before it's sent to the video output without buffering the whole frame. The main difference is the 2600 graphics hardware is typically reconfigured every line while the later consoles' graphics hardware is typically reconfigured every frame (although re-configuring between lines is usually also possible, and some games left it unchanged on some screen refreshes to save CPU time at the expense of lowering frame rate).
>from the hardware's perspective it's not even one line at a time, it's one dot at a time.
Mostly true, but I tried to make the description generic to as many systems as possible, so "line" is IMO more broadly accurate because a line is composed of dots. The Neo Geo is a tile + sprite system too, and it renders to line buffers.
A traditional IBM PC has a "dumb" framebuffer, where everything is done by the PC. Simply scrolling the background by 1 pixel basically means redrawing a lot of the screen, and you have to keep track of what graphics behind sprite would need to be redrawn after they move etc. As a bonus, on early consumer level 386 and 486 machines you have a mighty processor, but the graphics card is often still on a 16 bit 8MHz(ish) ISA bus. The PC does have an advantage that it's more flexible, so stuff like 3D was easier to do than on a tile-and-sprite setup (especially once we had stuff like VESA and PCI).
https://www.youtube.com/playlist?list=PLHQ0utQyFw5KCcj1ljIhE...