system
Given the following post, respond as if you're commenting on Reddit:
human
Why do computers and game consoles need to restart in order to install software updates?
gpt
A CPU can only work on stuff in its cache and the RAM of the device (be it PC / Mac / console / mobile / etc). However, such memory is volatile, and loses all its data if it is not powered. To solve this problem, secondary storage exists: hard disk drives, DVD drives, USB disks, flash memory, etc. They hold persistent data that is then transferred to the RAM as and when needed, to be worked on by the CPU. 

Now, when a computer boots up, a lot of its core processes and functions are pre loaded into RAM and kept there permanently, for regular usage. (The first of this stuff that loads is known as the *kernel*.) They are also heavily dependent on each other; eg, the input manager talks to the process scheduler and the graphics and memory controllers when you press a button. Because these are so interconnected, shutting one down to update it is not usually possible without breaking the rest of the OS' functionality*.

So how do we update them? By replacing the files *on disk*, not touching anything already in memory, and then rebooting, so that the computer uses the new, updated files from the start. 

*In fact, Linux's OS architecture and process handling tackles this modularity so well that it can largely update without a restart.