The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)

Motherboards and Form Factors

The motherboard, sometimes referred to as the planar or system board, is the central part of a computer that brings together all devices attached to the computer. The main components on the motherboard are the CPU (Central Processing Unit) and CPU chipset, expansion bus, I/O (Input/Output) interface, disk drive controllers, and Random Access Memory (RAM). The motherboard's main function is to distribute power and data to all devices attached to it.

Motherboards have different form factors. A form factor is simply the physical size and layout of the motherboard and its components. Several form factors and their features are described below.

Advanced Technology (AT) and Baby AT

Until 1997, the Advanced Technology (AT) and baby AT form factors were the most popular types of motherboards on the market. The main difference between the two is the width of the motherboards, themselves. The AT motherboard is 12 inches wide by 13 inches long. The baby AT is 9 inches wide by 10 inches long. See Figure 2.1 for the baby AT and its components.

Figure 2.1: Baby AT (Socket 7) motherboard and components.

The AT and baby AT form factors have the processor and memory socket locations toward the front of the motherboard. Very long expansion cards were designed to extend over them, which made removing the processor difficult. One had to take the expansion cards out first to remove the processor or to get to the memory. It is important to note that an AT power supply gives an output of 12V and 5V to the motherboard. Additional regulators are needed on the motherboard if 3.3V cards (peripheral component interface, or PCI) or processors are used.

This design was acceptable when clearance and cooling were not issues. With the advent of faster Pentium-class processors, which required more cooling and memory sockets that extended off the motherboards, a better motherboard design was needed.

Study the motherboard diagrams very closely. The A+ Core Test may show you a similar graphic representation that requires you to identify individual motherboard components.

LPX

In 1987, Western Digital introduced the Low Profile Extensions (LPX) motherboard form factor. This form factor was developed to meet the need for a slimmer desktop. This goal was accomplished based on the implementation of a riser card that extended from the motherboard and allowed expansion cards to be installed parallel to the motherboard.

NLX

As the need for more expansion slots and easier access to components increased, the LPX form factor was redesigned by Intel and named the NLX (InteLex) form factor. The NLX form factor moved the riser card from the center of the motherboard to the outside edge.

ATX

The ATX form factor was developed to solve the problems associated with the baby AT form factor design (Figure 2.2). This new design had many advantages that affected not only the motherboard, but the system unit and power supply, as well. The dimensions of the ATX form factor are 12 inches wide by 9.6 inches long. A mini ATX is typically 11.2 inches wide by 8.2 inches long.

Figure 2.2: ATX (Slot 1) motherboard and its components.

The ATX design provides the following advantages:

• Integrated I/O port connection. Baby AT motherboards have cables connecting them to the physical serial and parallel ports mounted on the system unit. With the ATX form factor, this connection is integrated into the motherboard. The ATX form factor uses a 20-pin plastic power supply connector. This is called a keyed connector, and it can be plugged into the motherboard in one direction only.

• Integrated PS/2 mouse connector. ATX motherboards have PS/2 mouse ports integrated into the motherboard. Most baby AT motherboards do not have a PS/2 mouse port. Older-style AT motherboards required a serial mouse. (The serial interface is covered in Chapter 8.)

• Easier access to components. The ATX motherboard was designed with functionality and accessibility in mind. It provides much easier access to components than the baby AT form factor and offers more room in general for additional components.

• Improved power supply connection. The new ATX form factor incorporated a single 20-pin connector in place of the pair of 6-pin connectors used on the baby AT motherboard.

• Support for 3.3V. The ATX motherboard supports 3.3V power from the ATX power supply. This voltage is used by most newer processors.

• ‘Soft switch' power support. The ATX power supply uses a signal from the motherboard to turn itself off. This feature enables you to use the power management utilities offered with newer operating systems to shut down a computer, as opposed to physically turning it off with the power button.

• Better airflow. With the ATX form factor, the processor is moved closer to the power supply, providing it with better air circulation and cooling. For proper air circulation, it is also important to replace any slot covers on the back of a computer that may be missing as a result of removed expansion cards.

Some very important facts to remember for the exam: most AT-style motherboards use a five-pin DIN keyboard connector. The ATX motherboard uses the smaller, six-pin mini-DIN keyboard connector, which is more commonly referred to as a PS/2 connector. The keyboard PS/2 connector is identical to the mouse PS/2 connector. In addition, motherboards use ‘jumpers' to configure or adjust certain onboard settings, such as the motherboard's clock speed (which is measured in megahertz, or MHz). Older motherboards used Dual In-line Package (DIP) switches to perform this function.

Micro-ATX

The micro-ATX form factor was developed to meet the need for a smaller and less expensive motherboard. The micro-ATX design offers all of the functionality of the traditional ATX, and is also backward compatible. The micro-ATX form factor is not listed in the CompTIA 2003 Objectives. But, because it is better to be safe than sorry, it is mentioned here. If you are interested in educating yourself further about this technology, the First International Computer, Inc. Web site offers some information: http://www.fic.com.tw/support/motherboard/faq.aspx?type=microatx#qid470