1. Microprocessor - This is the brain of your computer. It performs commands and instructions and controls the operation of the computer.
2. Memory - The RAM in your system is mounted on the motherboard. This is memory that must be powered on to retain its contents.
3. Drive controllers - The drive controllers control the interface of your system to your hard drives. The controllers let your hard drives work by controlling their operation. On most systems, they are included on the motherboard, however you may add additional controllers for faster or other types of drives.