ASROCK N68C-GS UCC User Manual page 24

Though this motherboard provides 24-pin ATX power connector,
it can still work if you adopt a traditional 20-pin ATX power supply.
To use the 20-pin ATX power supply, please plug your power
supply along with Pin 1 and Pin 13.
ATX 12V Power Connector
(4-pin ATX12V1)
(see p.11 No. 3)
20-Pin ATX Power Supply Installation
Please note that it is necessary
to connect a power supply with
ATX 12V plug to this connector.
Failing to do so will cause power
up failure.
2 4 2 4 2 4 2 4 2 4
12 24
1 13