There have been a lot of different mass storage methods over the relatively short lifespan of the computer ... an ISA board to provide a disk and clock for the old 8-bit bus.
At times, the System process may display a high disk or CPU usage for a few minutes. This is temporary and should not worry you. But if it persists frequently, you may need to look at a few things.
This guide provides an approach to Linux performance tuning, focusing on three key areas: CPU, memory, and disk optimization.