Motherboards and Buses - Upgrading and Repairing PCs - page 161

• Built-in double high external I/O connector panel —The rear portion of the motherboard
includes a stacked I/O connector area that is 6 1/4 inches wide by 1 3/4 inches tall. This
enables external I/O connectors to be located directly on the board and minimizes the need for
cables running from internal connectors to the back of the case as with Baby-AT designs.
• Single main keyed internal power supply connector —The ATX specification includes a
keyed and shrouded main power connector that is easy to plug in and install. This connector
also features pins for supplying 3.3V to the motherboard, helping to minimize the use of built-in
voltage regulators that are susceptible to failure.
See the Chapter 18 section, “ Motherboard Power Connectors , ” p. 870 .
• Relocated CPU and memory —The CPU and memory modules are relocated so they can't
interfere with bus expansion cards and can easily be accessed for upgrade without removing
any of the installed bus adapters.
• Relocated internal I/O connectors —The internal I/O connectors for the floppy and hard disk
drives are relocated to be near the drive bays and out from under the expansion board slot and
drive bay areas.
• Improved cooling —The CPU and main memory are designed and positioned to improve
overall system cooling compared to Baby-AT and older designs.
• Lower cost to manufacture —The ATX specification eliminates the need for the rat's nest of
cables to external I/O port connectors found on Baby-AT motherboards.
Figure 4.13 shows the typical ATX system layout and chassis features, as you would see them looking
in with the lid off on a desktop, or sideways in a tower with the side panel removed. Notice how
virtually the entire motherboard is clear of the drive bays and how the devices such as CPU, memory,
and internal drive connectors are easy to access and do not interfere with the bus slots.