ELI5: Why do computers become slow after a while, even after factory reset or hard disk formatting?

Part of that is degradation of the physical components.

Computers aren't exempt to the Third Law of Thermodynamics. We've designed them to be largely self correcting, but entropy will settle in on them eventually. It's just a matter of time.

Hard Disk Drives are reliant upon a physical motor, which spins the platter that contains data. The "read head" is also dependent upon a motor to physically reach the point on the disk where the data is stored. Those motors will break down over time. They will become slower, and eventually stop working entirely.

Solid State Drives become less efficient over time for different reasons. "Cells" where information can be stored have a finite number of read-write cycles, and all of them will eventually fail. The SSD Controller does its best to spread the load evenly over the drive, and generally has some "Extra" cells that it can swap in to replace dead cells, but the thing will eventually fail entirely. The time it takes to access data increases as more cells die, and the controller has to do increasingly complicated operations to keep the drive alive.

Even the basic components of the computer undergo some degradation, even though they don't have moving parts. Thermal Expansion causes most of that damage. Metal components expand faster than the silicon does, and that causes a few microscopic problems... such as a circuit getting a little bit more resistance to electrons flowing through it, or a circuit getting physically longer by an imperceptible amount. Transistors become less "snappy" over time, taking a little longer to flip open or closed.

All of these delays are in the picoseconds, but they add up.

/r/explainlikeimfive Thread