Hardware Reference
In-Depth Information
This means the total power-handling capacity of this connector is only 58 watts. Drawing more
power than this maximum rating through the connector will cause it to overheat.
Combining the 20-pin main plus the auxiliary power connector would result in a maximum power-
delivery capability to the motherboard of 309 watts.
Few motherboards actually used this connector, and few power supplies included it. Generally, if a
motherboard includes this connector, you need a power supply that has it as well, but if the power
supply includes the auxiliary connector but the motherboard does not, it can be left unconnected.
Starting in 2000, both motherboards and power supplies began including a different additional
connector that was a better solution than the auxiliary connector. The most recent power supply form
factor specifications have removed the auxiliary connector, rendering it an obsolete standard in
modern systems.
ATX12V 2.x 24-Pin Main Power Connector
Starting in June 2004, the PCI Express bus first appeared on motherboards. PCI Express is a type of
serial bus with standard slots having a single channel or lane of communications. These single-lane
slots are called x1 slots and are designed for peripheral cards such as network cards, sound cards,
and the like. PCI Express also includes a special higher-bandwidth slot with 16 lanes (called an x16
slot ), which is especially designed for use by video cards. During development it was realized that
PCI Express x16 video cards could draw more power than what was allowed by the existing 20-pin
main and 6-pin auxiliary power supply connectors, especially when it came to +12V power.
The problem was that the 20-pin main connector had only a single +12V pin, but the new video cards
required more +12V power than a single pin could safely deliver. The +12V connector that had
already been added, as discussed in the next section, was specifically for the CPU and was
unavailable to other devices. Rather than add another supplemental or auxiliary connector as it had
done before, Intel eventually decided that it was finally time to upgrade the main power connector to
supply more power.
The result was officially called ATX12V 2.0 and was released in February 2003. ATX12V 2.0
included two major changes from the previous ATX12V 1.x specifications: a new 24-pin main power
connector and the elimination of the 6-pin auxiliary power connector. The new 24-pin main power
connector included four more pins supplying additional +3.3V, +5V, and +12V power plus a ground.
The inclusion of these extra pins delivered extra power to satisfy the power requirements for PCI
Express video cards drawing up to 75 watts, but it also made the older 6-pin auxiliary connector
unnecessary. The pinout of the new 24-pin main power connector started to be implemented in
motherboards in mid-2004. The motherboard connector pinout is shown in Table 18.10 , and the PSU
connector is shown in Figure 18.24 .
Table 18.10. ATX12V 2.x 24-Pin Main Power Supply Connector Pinout (Motherboard
Connector)
 
 
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