Difference between AT and ATX Power Supply

In a computer system, power supply or power supply unit is a hardware component that supplies required electrical power to other components of the computer system. The power supply unit converts a 220 V AC (Alternating Current) supply into a low voltage DC (Direct Current) supply.

The major function that a computer power supply unit performs are −

• Rectification − Conversion of alternating current supply into direct current supply.

• Voltage transformation − Decreases the high AC voltage into low voltages.

• Voltage regulation − Regulates the output voltage to make it constant even when the input voltage is fluctuating.

There are several types of computer power supply units available in market. For personal computers, the two most widely used power supply standards are namely, AT (Advanced Technology) and ATX (Advanced Technology Extended). The fundamental difference between AT and ATX power supplies is in their physical size and the placement of the motherboard connectors

In this article, we will discuss the two types of power supplies namely – AT and ATX power supplies, and important differences between them. So, let's get started with a basic introduction of AT and ATX power supplies.

What is AT Power Supply?

AT power supply stands for Advanced Technology power supply. AT power supply was most commonly used in personal computers in the 1990s and early 2000s. AT power supplies are large sized and bulky power supply units.

They consists of two main power connectors −

• A 20-pin power connector for the motherboard

• A 4-pin power connector for the processor

There are many other power connectors for peripherals like hard disk drives, optical drives, CPU fan, etc.

The AT power supply standard for personal computers was developed by IBM in the 1980s. Hence, in that era, it became the standard power supply for all the IBM compatible personal computers.

AT power supplies are capable for providing a maximum output of 250 Watts. The major disadvantage of the AT power supply unit is that it does not support modern power saving features like standby power. Hence, the personal computers with AT power supply consumes more electricity even they are not in use.

Another significant disadvantage of AT power supply is that it has power switch located at back of power supply which made it very difficult to turn the computer ON and OFF without physically accessing the power supply unit.

These days, the AT power supply unit is not being used in modern personal computers, instead they use ATX power supply unit.

What is ATX Power Supply?

ATX stands for Advanced Technology Extended. It is a new power supply standard developed in 1995 as a replacement for the AT (Advanced Technology) power supply standard.

ATX power supply standard is a more efficient and reliable power supply standard. ATX power supply unit is capable to provide a relatively higher maximum output of up to 1600 Watts.

The ATX power supply unit consists of a 20-pin or 24-pin main power connector for the motherboard. It also has many other power connectors for peripherals like hard disk drives, optical drives, CPU fan, graphics card, etc.

ATX power supplies are available in several sizes and form factors, and hence, they can fit into different types of CPU cases. The most significant advantage of the ATX power supply over AT power supply is that it supports modern power saving features like standby power. Hence, it makes computers to consume less power while not in use. Another major advantage of the ATX power supply is that it has a power switch which is placed on the front of the CPU case. It makes the computer to turn ON and OFF easier without physically accessing the power supply unit.

Overall, ATX power supply is more advanced and reliable computer supply unit as compared to the older power supplies. This is because, it ensure the stable and reliable operation of the personal computer.

Difference between AT Power Supply and ATX Power Supply

The following table highlights all the significant differences between AT power supply and ATX power supply −

Parameter	AT Power Supply	ATX Power Supply
Full Form	Advanced Technology Power Supply.	ATX Power Supply stands for Advanced Technology Extended Power Supply.
Main Power Connectors	AT power supply has two main power connector, one for the motherboard and the second one for the CPU.	ATX power supply has a single power connector for the motherboard.
Number of Pins in the Motherboard Power Connector	AT power supply has 20-pins in the motherboard power connector.	ATX power supply has either 20- pins or 24-pins in the motherboard power connector.
Connectors for Peripherals	AT power supply has a limited number of power connectors for peripherals.	ATX power supply has relatively more number of power connectors for peripherals.
Size and Weight	AT power supply is larger in and size and heavier in weight.	ATX power supply is compact in size and lighter in weight.
Cooling Fan	AT power supply has a larger cooling fan typically located at back of the power supply.	ATX power supply has a smaller cooling fan that is located on the bottom of the power supply.
Fan Speed Control	AT power supply does not have the fan speed control feature.	ATX power supply has fan speed control feature which helps to reduce the noise and improve the cooling.
Power Switch	AT power supply has a power switch located on the back of the power supply.	ATX power supply has a power switch located on the front of the CPU case.
Modern Power- Saving Features	AT power supply does not support modern power saving feature like standby mode.	ATX power supply supports modern power saving features.
Power Consumption	Computers with AT power supply consume more power even when they are not in use.	Computers with ATX power supply consumes less power when they are not in use.
Voltage Tolerance	The voltage tolerance in the case of AT power supply is of ± 5 %.	The voltage tolerance in the case of AT power supply is of ± 3 %.
Form Factor	AT power supplies have the design that is compatible to AT- CPU cases.	ATX power supplies have design compatible to ATX-CPU cases.
Safety Features	AT power supply does not have any safety feature.	ATX power supply provides protection against over-voltage, over-current, and short-circuit.
Efficiency	AT power supplies are less efficient and generate more heat.	ATX power supplies are more efficient and generate less heat.

Conclusion

AT (Advanced Technology) power supply was the standard power supply used in PCs in the 1990s and early 2000s, whereas the ATX (Advanced Technology Extended) power supply was the standard power supply used in modern personal computers. ATX power supply is basically an improved version of the AT power supply.

ATX power supply offers several benefits over AT power supply, such as higher efficiency, modern power saving features, extra peripheral connectors, improved safety features, etc.

Hence, while selecting a power supply unit for a personal computer, it is always important to consider that the power supply unit offers all the feature which are required for the reliable and stable operation of the computer.