This document provides an overview of the BTX motherboards for personal computers.
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Saturday, October 19, 2013 6:14 PM
The BTX Motherboard
Balanced Technology Extended (BTX) is a motherboard form factor specification that Intel released in September 2003, with 1.0a and 1.0b updates released in February 2004 and July 2005, respectively. BTX was designed to address the ever-increasing component power and cooling requirements, as well as enabling improved circuit routing and more flexible chassis designs. However, the recent trend toward more power efficient dual-core processor designs has slowed the need for the benefits inherent in the BTX standard, which has in turn slowed the adoption of BTX, causing Intel to announce in late 2006 that it was abandoning future BTX development. BTX was popular in many mass-produced retail-branded PCs sold between 2005 and 2007, such as those by Dell, Gateway, and others. Since then the BTX form factor has largely been abandoned.
BTX is not backward-compatible with ATX or other designs. A full-size BTX board is 17% larger than ATX, allowing room for more integrated components onboard. The I/O connectors, slots, and mounting holes are in different locations than with ATX, requiring new chassis designs. However, the power supply interface connectors are the same as in the latest ATX12V specifications, and newer ATX, TFX, SFX, CFX, and LFX power supplies can be used. The latter two power supply form factors were specifically created to support compact and low-profile BTX systems. The primary advantages to BTX include optimized inline component layout and routing, optimized airflow path, a support and retention module (SRM) for heavy heatsinks, scalable board dimensions, low-profile options, and flexible power supply designs with connector types that are compatible with ATX designs.
It was designed to alleviate some of the issues that arose from using newer technologies (which often demand more power and create more heat) on motherboards compliant with the circa-1996 ATX specification. The ATX and BTX standards were both proposed byIntel. Intel's decision to refocus on low-power CPUs, after suffering scaling and thermal issues with the Pentium 4, has added some doubt to the future of the form factor. The first company to implement BTX was Gateway Inc, followed by Dell and MPC. Apple's Mac Pro utilizes some elements of the BTX design system as well but is not BTX compliant, rather using a proprietary form factor.
BTX includes three definitions of motherboard size, as shown in Table 4.1.
Table 4.1. BTX Motherboard Form Factors
Size Versus BTX
12.8 in. (325mm)
10.5 in. (267mm)
134 sq. in. (867 sq. cm)
10.4 in. (264mm)
10.5 in. (267mm)
109 sq. in. (705 sq. cm)
8.0 in. (203mm)
10.5 in. (267mm)
84 sq. in. (542 sq. cm)
Each board has the same basic screw hole and connector placement requirements. So, if you have a case that fits a full-size BTX board, you can also mount a microBTX or picoBTX board in that same case (see Figure 4.10). Obviously, if you have a smaller case designed for MicroBTX or picoBTX, you won’t be able to put the larger microBTX or BTX boards there.
BTX requires up to 10 mounting holes and supports up to seven slots, depending on the size, as shown in Table 4.2.
Table 4.2. BTX Motherboard Mounting Holes
A, B, C, D, E, F, G, H, J, K
A, B, C, D, E, F, G
A, B, C, D
BTX also clearly specifies volumetric zones around the motherboard to prevent interference from the chassis or internal components such as drives, which allows for maximum interchangeability without physical interference or fit problems.
With processors exceeding 100W in thermal output, as well as voltage regulators, motherboard chipsets, and video cards adding to the thermal load in a system, BTX was designed to allow all the high-heat-producing core components to be mounted inline from front to back, so that a single high-efficiency thermal module (heatsink) can cool the system. This eliminates the need for an excessive number of fans. The thermal module includes a heatsink for the processor, a high-efficiency fan, and a duct to direct airflow through the system. Extra support for the thermal module is provided under the board via an SRM, which provides structural support for heatsinks that are much heavier than allowed in ATX designs (see Figure 4.11).
Figure 4.11. BTX thermal module containing a processor heatsink and fan.
BTX uses the same power connectors as in the latest power supply form factor specifications, including a 24-pin main connector for the board and a 4-pin ATX12V connector for the CPU voltage regulator module. The particular power supply form factor used depends mostly on the chassis selected.
A typical tower system has components arranged as shown in Figure 4.12.
Figure 4.12. BTX tower chassis layout.
From Figure 4.12, you can see that the main heat-producing core components are centrally located inline from front to rear, allowing the most efficient thermal design. Air flows from front to rear through the center, cooling the processor, motherboard chipset, memory, and video card.
To support the heavy processor heatsink and thermal module assembly, an SRM is mounted under the board. The SRM is essentially a metal plate affixed to the chassis under the board, and the thermal module is bolted directly to the SRM instead of to the motherboard. This helps carry the weight of the module and prevents excessive loads from being applied to the processor and motherboard, especially during the shipping and handling of the system.
The BTX I/O connector area is similar to ATX, except that it is at the opposite side of the rear of the board. The size of the area is slightly shorter but wider than ATX, allowing a large number of interfaces and connectors to be built into the motherboard.
Systems using BTX were produced primarily from 2005 through 2007 by companies such as Dell and Gateway. After that, a lack of new BTX motherboards and cases forced most system manufacturers and builders to abandon BTX and revert to the more popular ATX-based form factors. Other large manufacturers such as HP never jumped on the BTX bandwagon, instead staying with ATX-based systems. Because of the lack of BTX component popularity and other problems, I recommend avoiding BTX systems and components such as motherboards and chassis because they will be difficult to upgrade or replace in the future. ATX remains by far the most popular and recommended form factor for system builders and upgraders.