Editing IBM Personal Computer AT (section)

=== Power supply ===
The IBM PC AT came with a 192-watt [[switching power supply]], significantly higher than the 130-watt XT power supply.

According to IBM's documentation, in order to function properly, the AT power supply needed a load of at least 7.0 amperes on the +5&nbsp;V line and a minimum of 2.5 amperes on its +12&nbsp;V line. The power supply would fail to start unless these minimum load requirements were met, but the AT motherboard did not provide much load on the +12&nbsp;V line. To solve this problem, entry-level IBM AT models that did not have a hard drive were shipped with a 5-ohm, 50-watt resistor connected on the +12&nbsp;V line of the hard disk power connector. In normal operation this resistor drew 2.4 amperes (dissipating 28.8 watts), getting fairly hot.<ref name="Mueller2011">{{cite book|author=Scott M. Mueller|title=Upgrading and Repairing PCs|year=2011|publisher=Que Publishing|isbn=978-0-13-268218-3|page=882|edition=20th}}</ref>