An ATX power connector is a 20- or 24-pin primary connector that specifically plugs and supplies power into an ATX-type computer motherboard. This in turn distributes power to internal components, such as the CPU, memory module, hard disk and graphics card.
Unlike older motherboard power connectors, an ATX power connector features a key-in clip or orientation clip that holds the connector securely in place and ensures the connector is plugged in the right orientation. This feature eliminates the risk of incorrectly connecting power that can short circuit and damage motherboards.
According to Tech-FAQ, the ATX standard was developed by Intel in 1995 as a replacement to the older AT format.