Baby AT Form Factor

The Baby AT form factor is so named because it is a smaller version of the original AT form factor. It has the same height and depth, but is about 2" narrower. Since it is "similar but smaller", the Baby AT power supply will fit both in Baby AT form factor cases and in full-size AT cases as well, in both tower and desktop styles. It has the same output motherboard and drive connectors as the AT. Due to this flexibility, and the fact that it was introduced at around the time that PCs began to really grow in popularity, the Baby AT form factor reigned as the most popular design for over a decade--far longer than any other. From around 1985 to 1995, a large percentage of new PCs were Baby ATs (though later on LPX form factor power supplies came to be used in many Baby AT systems.)

Diagram of the side and rear views of a Baby AT form factor power supply,
with approximate dimensions. Note that the dimensions are very similar
to that of the AT form factor; essentially the "overhang" shown on the right side
of the AT power supply rear view was removed because smaller Baby AT
motherboards and supplies no longer required it. A desktop version also exists
that is the same except for the addition of an external toggle switch on the side
(as shown in the AT desktop style diagram on the AT form factor page.)

Original image � PC Power & Cooling, Inc.
Image used with permission.

The Baby AT power supply was made in both a tower and desktop configuration, like the full-sized AT, and like the full-sized AT these differ only in the type of power switch used. Unlike the full-sized AT, however, in the Baby AT form factor tower versions became much more popular. Even in many desktop systems, tower-style power supplies began to be installed for the simple reason that most users prefer having a power switch on the front of the case and not in the rear.

This form factor has now been replaced in new systems by the ATX and other form factors. However, the huge installed base has given Baby AT momentum and given manufacturers of new components incentive to provide upgrade options for the millions who still use these systems.