Hardware Reference
In-Depth Information
The ATX main power connector is either a 20-pin or a 24-pin connector, which, if standard terminals
are used, is rated for up to 6 amps of current per terminal. If the connector were upgraded to HCS
terminals, the rating would increase to 9 amps per terminal, and if upgraded to Plus HCS terminals,
the rating would increase further to 11 amps per terminal. Prior to March 2005, all the power supply
form factor specifications called for using standard terminals, but all the ratings from March 2005 to
the present have changed to require HCS terminals instead. If your power supply connector has been
overheating, you can easily install HCS or Plus HCS terminals to increase the power-handling
capability of your connector by 50% or more.
By counting the number of terminals for each voltage level, you can calculate the power-handling
capability of the connector, as shown in
Table 18.7
.
Table 18.7. ATX 20-Pin Main Power Connector Maximum Power Handling Capabilities
This means the total power-handling capacity of this connector is only 251 watts if standard terminals
are being used, which is lower than most systems need today. Unfortunately, drawing more power
than this maximum rating through the connector causes it to overheat. I'm sure you can appreciate how
inadequate this has become today; for example, it certainly doesn't make sense to manufacture a 400-
or 500-watt power supply if the main power connector can handle only 251 watts without melting!
That would be like building a car that could go 200 mph and then equipping it with tires rated for only
100 mph. Everything would be fine until you exceeded the tires' rated speed, after which the results
would not be pretty.
This is why the official power supply form factor specifications were updated in March 2005 to
include HCS terminals, which have 50% greater power-handling capability than the standard
terminals. Using HCS terminals, the power-handling capability of the 20-pin main connector alone
increases to 377 watts, which is more than most systems need to run the entire system through all the
connectors combined.
Six-Pin Auxiliary Power Connector
As motherboards and processors have evolved, the need for power has become greater. The
terminals in the main power connector are rated for 6 amps (A) using standard terminals, which
