Hardware Reference
In-Depth Information
The RTC in the original PC was notoriously inaccurate, so starting with the IBM AT in
1984, IBM added a separate 32.768KHz crystal to count time independent from the speed
ofthe system. This crystal isusedonall modern motherboards aswell.
Figure 3.46
shows
a 32.768KHz crystal next to a chipset South Bridge or I/O controller hub, which contains
the RTC circuitry and CMOS RAM.
Figure 3.46
Chipset South Bridge (I/O controller hub) incorporating an RTC, along with the 32.768KHz
clock crystal.
