Explain Like I'm Five

Yes - it's been the job of the DRAM controller for almost the entire history of computing. But that's still a part of the computer and if it stops working then your RAM will go blank in a fraction of a second

It's been a very long time since my computer engineering course, and we didn't cover this topic specifically, but I highly doubt it's a full dump and reload. What likely happens is each ram address has a ttl flag or some way for the CPU to know when to rewrite the data, and it does it as needed.

Plus, the bus between the CPU and ram is ridiculously fast. Your pc could dump and reload all of its ram in the time it takes you to blink. And, with multiple cores, the task can be allocated to a single core, or divided up among all of them.

Some very early systems did do it at kernel level, but yeah you are correct. Though I'd also consider the dram chips to be part of the computer and DRAM refresh makes up a good part of your phones battery consumption at standby.

If you ever have the chance to use an old Apple II computer, run a text mode program, wait til the owner is looking in the other direction and turn the power off and back on quickly.

For about a second, before you hear the loud BOOP and the screen clears, you'll see whatever was on the screen just before you powered it off. But a few characters will be corrupted. Try it again, and wait a half a second longer than before. More characters will be corrupted.

For that brief second you're looking at the contents of the video RAM, then the ROM (Apple called what we call BIOS now "ROM") clears the contents and puts up the familiar text banner. The longer the power stays off, the more the contents of those RAM cells decay, and any bit flip will show up as a different character at the corresponding location on the screen.

On a side note, there was an article in the early '80s in Circuit Cellar by Steve Ciarcia showing how you could make a rudimentary digital camera by prying the top off a DRAM chip (some were ceramic with metal lids, or just metal cans) and adding a CCTV camera lens at the right distance. Light can deplete the charge in DRAM cells even faster, and by writing all 1s to the memory, exposing it to light, and reading back the contents, you could get a black and white image of whatever's shining on the chip.

srsly... https://en.wikipedia.org/wiki/Memory_refresh

Dynamic RAM tracks bits by using a capacitor for each bit. Caps' charge bleeds out so you have to top it off again every so often. The way you do that is to just write the same data back again. So it reads and writes the same data to itself every refresh. The opposition to this is static RAM which does not use a capacitor and is just a clever arrangement of transistors. No refresh needed. It's not typically used commercially except under special requirements, though as transisters are significantly more expensive. So the refresh strategy is the better choice for consumer hardware. DRAM has been dominant for decades.