Editing IBM PC AT (5170) (section)

== Power Supply ==

The 5170 includes a '''192 W switching power supply''' with two motherboard connectors (P8/P9). It requires a minimum load of '''7.0 A on +5 V''' and '''2.5 A on +12 V''' to start. Because the AT motherboard provides little +12 V load on its own, entry-level submodels that did not include a hard drive shipped with a '''5 Ω 50 W resistor''' fitted to the +12 V line of the hard drive power connector to satisfy the minimum load. The resistor draws roughly 2.4 A (about 29 W) in normal operation and gets fairly hot.

The AT serial port is built around the '''16450 UART''', which (like the 8250 in the PC/XT) has only a single-byte buffer; high-speed serial work is problematic without a 16550-equivalent replacement.