system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is a hard disk drive able to be simultaneously read and written to?

My 5TB external drive is always being backed up to the cloud, but I can still read/write from/to it without any trouble. Since it relies on mechanical arms to access the data, how can it do all of this at the same time?
gpt
it doesn't read and write at the same time. It can't do that.

what you are seeing is the operating system caching the reads and writes, so that it can do a little reading, then  little writing, then a little more reading, etc, so that it SEEMS it is doing both at once.