This document provides an overview of the full size AT motherboard for personal computers.
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Saturday, October 19, 2013 6:14 PM
The Full Size AT Motherboard Form Factor
The full-size AT motherboard form factor matches the original IBM AT motherboard design. This allows for a large board of up to 12 inches wide by 13.8 inches deep. The full-size AT board first debuted in August 1984, when IBM introduced the Personal Computer AT (advanced technology). To accommodate the 16-bit 286 processor and all the necessary support components at the time, IBM needed more room than the original PC/XT-sized boards could provide. So for the AT, IBM increased the size of the motherboard but retained the same screw hole and connector positions of the XT design. To accomplish this, IBM essentially started with a PC/XT-sized board and extended it in two directions (see Figure 4.3).
A little more than a year after being introduced, the appearance of chipsets and other circuit consolidation allowed the same motherboard functionality to be built using fewer chips, so the board was redesigned to make it slightly smaller. Then, it was redesigned again as IBM shrank the board down to XT-size in a system it called the XT-286 (introduced in September 1986). The XT-286 board was virtually identical in size and shape to the original XT, a form factor which would later be known as Baby-AT.
The keyboard connector and slot connectors in the full-size AT boards still conformed to the same specific placement requirements to fit the holes in the XT cases already in use, but a larger case was still required to fit the larger board. Because of the larger size of the board, a full-size AT motherboard only fits into full-size AT desktop or tower cases. Because these motherboards do not fit into the smaller Baby-AT or mini-tower cases, and because of advances in component miniaturization, they are no longer being produced by most motherboard manufacturers—except in some cases for dual processor server applications.
The important thing to note about the full-size AT systems is that you can always replace a full-size AT motherboard with a Baby-AT (or XT-size) board, but the opposite is not true unless the case is large enough to accommodate the full-size AT design.
This hardware is considered obsolete and is explained here for reference purposes only.
The motherboard pictured here can support the following technologies:
Any Intel 486 based central processing unit designed on the left hand side of the motherboard.
(6) 8 bit ISA slots designed on the right hand side of the motherboard.
(2) 16 bit EISA slots designed at the bottom of the motherboard.
(8) Single Inline Memory Modules (SIMM's).
(1) AT Keyboard.
Other components need to plug into the ISA or EISA expansion slots on the motherboard.
This motherboard has no built in support for hard disk or optical storage drives. A seperate hard drive controller card was required to control a hard disk sub system.
Old and obsolete computer hardware.
Did set the standard for future AT based motherboards.
Designed for 8088, 80286, 80386, and 80486 based computers.