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Different between AT and ATX power supply??

Posted on 2001-08-02
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Can Some 1 tell me the different between at and atx power supply??

** i need the answer in detail **

hope to hear ur answer soon...thankx!!
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Question by:hwtang5401
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Don Thomson earned 100 total points
ID: 6345030
The AT Power supply if used for any Motherboard either 286/386/486 or Pentium 1  up to 233MHz

Ath ATX Power Supply is used on MB that are PentiumII class or higher

The Power connection on an AT powersupply has two connectors (blacks go together)

The ATX Powersupply has a single long connector that is keyed (you can't screw it up)

The ATX motherboard and case  has a momentary connect power switch (on-off)  that shorts out when you press it - Like a doorbell. This sends a signal to the motherboard to turn on the ATX Power Supply.  

The AT Case On-off switch is a toggle - Press once for on - once for off.   It actually cut off the power from the main 120V cable that feed the power supply.

The two powersupplies are NOT interchangable in any manner shape or form

AT PS works only in an AT style case and with an AT style MB

ATX PS works only on an ATX Case and with an ATX style MB

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by:hwtang5401
ID: 6345216
Dear DTHConsulting

Can u give me the different more detail on physical component??

Thankx!!
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by:Don Thomson
ID: 6345246
The main differance in appearance is the Mother board power connector - The AT  Power supply has several rectangular 4 pin RBBY  (plus one or more for the floppy power connectors for drives cds etc

In addition it has two other connectors that plug into the Motherboard. They are slightly longer and have 5 or 6 wires on them with one end of each having black wires - these always go to the centre when connected to the MB

The ATX power supply has the same device connectors and ONE long connector for the Motherboard. with two rows of wires.  Hard to miss
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by:frache
ID: 6345478
Your answer is here :
http://www.compute-aid.com/atxspec.html

Another thing :
AT power supply : supply +5,-5V,+12V,-12V voltages
ATX power supply  : supply  +5,-5V,+12V,-12V and 3,3V voltages.

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by:RoadWarrior
ID: 6347387
Sorry DTH, but.....


>>>The AT Power supply if used for any Motherboard either 286/386/486 or Pentium 1  up to 233MHz
>>> Ath ATX Power Supply is used on MB that are PentiumII class or higher

AT power supplies, cases and board form factors were the common standard from 286 systems right through Pentium 1 systems, but from then on became less common as most manufacturers switch to ATX. However, many people still had AT cases that they wanted to upgrade and there was/is quite an exess stock of AT cases on the market, so therefore AT didn't quite die with the last of the Pentium 1 class, PII/II, super 7 up to 550 Mhz boards are and have been available for AT form factor cases and PSUs.

>>>The two powersupplies are NOT interchangable in any manner shape or form

>>> AT PS works only in an AT style case and with an AT style MB

>>>ATX PS works only on an ATX Case and with an ATX style MB

There are some wierd mixtures around, for instance some motherboards in either AT or ATX form factor come with both AT and ATX power supply connectors on board, so you could have AT form boards in ATX cases, and ATX form boards running of AT PSUs. Just as a "for instance" I have an ATX form motherboard in a full AT case, running off an AT PSU, because this particular motherboard happens to have an AT power connector.

The most inportant thing as Frache mentioned and links to, is that ATX have a 3.3V supply, very important for modern motherboards, converting from 5v onboard just makes excess heat. Also ATX PSUs are designed from the ground up for such features as power management and soft power off, whereas AT PSUs with this feature have often had it added as an afterthought.

regards,

Road Warrior
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by:Don Thomson
ID: 6348697
Road Warrior - Your right of course - There were some manufacturers that used ATX powersupplys in earlier version but for 95% of the cases this was only on proprietary systems like PS2s.  There were also some Pentium II/Celeron MB that would still work with AT powersupplies  but again very few.

I believe that hwtang5401  was trying to get an answer to "how do I tell the difference.  Unfortunatly - unless it's marked on the case - you can't tell if the PS has 3.3V  without it being working in a system.. The easiest way to tell is based on the size of the MB plug and the fact that the AT powersupply will come with a heavier cable which goes to the power switch (4-wires)

Again the main thing is that you cannot ever use an AT power supply in a system that requires an ATX one and visa versa.

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by:frache
ID: 6349094
Note :
Gigabyte sells motherboard with ATX and AT power supply connectors. Exemple SG586GA ....
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by:Don Thomson
ID: 6349133
frache  - Yes I have seen one or two of those combo boards. In those cases you have to handle the on/off switch differently. Can be a pain if the case only supports one or the other.
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Expert Comment

by:magarity
ID: 6349651
I think hwtang needs to tell why this information is needed otherwise all these attempts at describing the differences are just guesswork to the mystery hidden question.
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by:pbessman
ID: 6350309
I have had these systems with both AT and ATX connectors.  There is actually a jumper on some of them that needs to be set based on which one you will be using.  Later models became jumperless.  I had preferred using the AT set up on systems that would be "always on" as it eliminates a lot of the challenges of the ATX advanced power management setups.  If you intend to use any of the new features like Wake on LAN, Wake on Ring or other Wake options it would require you to use the ATX power supply.  Since the AT systems are a hardware "On-Off" as DTH consulting mentioned, they cannot be controlled by motherboard events.  An ATX 2.0 compliant power supply can be set to provide the motherboard with reduced current to allow these "wake" events to occur.  Not all ATX power supplies will permit these functions.

Which brings me to Magaritys' comment, "just guesswork to the mystery hidden question."  What is it that hwtang5401 really needs to know beyond the fact that AT is hardware on and off with a positive switch while ATX provides switching using momentary switch and can be software controlled?
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by:pbessman
ID: 6350312
Possible Homework question???
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by:magarity
ID: 6350527
"Possible Homework question???"

Maybe, but I suspect that this power supply of person's AT powered computer died and since ATX are a lot more common these days he/she is trying to rewire a new ATX as the replacement.
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by:Don Thomson
ID: 6350618
If what magarity says is true - DON'T
You'll probably end up blowing your MB
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by:pbessman
ID: 6350632
Some motherboards have BOTH, maybe he is faced with this decision of what to get.  If this be the case go ATX(newer technology) as it will be supported by future boards.
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by:pbessman
ID: 6350663
The prices for AT cases are a lot lower as well it seems.  You can get a decent 250W one for 29.00.  The ATX of same brand and looks is 49.00.
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by:RoadWarrior
ID: 6350806
Heh, just to further confuse things some manufacturers like Acer  have a power management version of AT supplies, it's got exactly the same connector as an AT supply, but it also has an extra power management connector to the supply, that connects to the motherboard and no hard off switch on the front, the front power switch is a simple push to make, the switch on the rear actually controlling power.  I have also seem AT supplies that support suspend, and soft power off, you have to have en extra pushbutton or connect your case reset button to the PM jumper on the motherboard to power them up in "off" mode without having to use the hard power button. In suspend the keyboard or selected event wakes them up.
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by:pbessman
ID: 6350912
I had a 100.00 enlight case that had a lock on it that prevented "unauthorized" users from being able to access the system using a mouse or keyboard.  Since the motherboard had both connections it would only go so far.  Microsoft notes that the message that appears, "it is now safe to turn off your computer" which is a remnant of the AT technology is by design and is not a problem.  I don't see it everytime I shutdown, but often enough to notice it on my ATX systems.
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Author Comment

by:hwtang5401
ID: 6351439
Dear solutioner;

This is y i come here and ask the question...
--> coming exam is going to ask this question...but my text book didnt cover those thing lohh

--> somemore is, i really dont have time to go to library to seek for those information

Thankx
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