system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is actually happening when a computer/smartphone is booting? Why isn't it usuable immediately upon turning it on?
gpt
When you interact with a computer, you're interacting with software that lives in "memory". However, for the vast majority of computing devices, memory can only retain the software while it receives power. 

There are other storage areas on computing devices that can retain software and data even while powered off. On most computers, that's a combination of BIOS (a special computer chip that contains the basic simple operating instructions) and the hard drive. On a smartphone, it's a special kind of memory that's considered "non-volatile" because it doesn't get erased when the power goes away. These storage places are much slower than normal memory. 

When a computer boots up, it copies or "loads" the software that it will use from whatever slower storage it uses into its fast storage, memory, so it can operate at the speed you expect.