Explain how the system unit components communicate?

Answer 1

They communicate using data Busses using the Chipsets which are the North and South Bridge; the faster components such as the CPU, RAM and Accelerated Graphics Port are controlled by the Northbridge and it communicates to the CPU via the front side buss, the RAM via the Memory Buss and the Accelerated Graphics Port via the Graphics Buss.

http://en.wikipedia.org/wiki/Northbridge_%28computing%29

The Southbridge communicates to the Hard Disk via the ATA Buss, the USB, PCI and BIOS via the LPC Busses; you may find this opinion differs. the S-bridge may communicate to the PCI via the PCI Buss and the USB via the USB Buss.

http://en.wikipedia.org/wiki/Southbridge_%28computing%29

http://en.wikipedia.org/wiki/File:Schema_chipsatz.png

HOPE THIS HELPS :-)