![[Bytes Link logo]](../../../cgif/bytelnk2.gif)
Motherboard Technology 2001
by By Herbert Wong, Jr., NOCCC Hardware SIG Leader - November 03, 2001 at 00:48:03:
The motherboard (also known as the mainboard) is the backbone of the personal computer. Except for mass storage and power supply, every major component of the computer is (or can be) directly or indirectly integrated into the motherboard.Form Factor
The form factor refers to the physical size and shape of the motherboard. In addition, the standardized placement of mounting screw holes, keyboard connector, expansion slots (ISA, PCI, AGP, etc.), etc. In the latest generations, form factors specify the placement of input-output ports such as USB, PS/2 keyboard, PS/2 mouse, serial, parallel, etc.
High frequency operation mandates the intimate placement of high-density integrated circuit components on the motherboard. As a result, motherboards are physically smaller than in the past. As a result, the earliest IBM PC and IBM PC-AT (known simply as AT) motherboard form factors are obsolete.
The baby-AT (BAT; 9 inches wide by 10 inches long) is a smaller version of the AT form factor (12 inches wide). Its most annoying flaw was the placement of the microprocessor (and, hence, microprocessor cooling fan) in the direct path of several expansion slots. As a result, medium length or longer cards frequently could not be used since they would be inside the cooling fan. In addition, memory slots and disk drive connectors were often placed behind hard disk drive bays (mountings), necessitating the removal of the entire drive bay to simply unplug a connector or add a memory module.
The baby-AT motherboard fixed placement of the keyboard connector (AT mini DIN type) to align with a hole in the case. Parallel and serial ports were simply a series of parallel pins sticking up from the motherboard. The motherboard's power connector required a pair of identically keyed power supply cables that if interchanged would destroy the motherboard.
The ATX (12 inches wide by 9.6 inches long) and mini-ATX (11.2 inches wide by 8.2 inches long) form factors attempt to correct the deficiencies of the baby-AT. The PS/2 keyboard, PS/2 mouse, USB, parallel port, and serial port connectors require no additional attachments or cables. They are simply exposed through cutouts in the case when the motherboard is properly mounted. This reduces component cost, speeds installation, and eliminates cable reversal errors. The motherboard's revamped power connector is a single unit that cannot be reversed.
The ATX design allows software control of the power supply. As a result, there is a constant flow of power to an ATX motherboard and removal of components from the motherboard can result in damage unless the power supply is deactivated. Some power supplies have a switch to shut off AC main power, even though this switch is not in the Intel ATX specifications. Otherwise, you will have to unplug the power cord to disconnect AC main power.
Other motherboard form factors are primarily used in small or low profile cases. The MicroATX (9.6 inches by 9.6 inches) uses standard ATX mounting for standard or micro-tower desktop cases.
The LPX is a smaller variant of the baby-AT. The Intel NLX (8.8 inches wide by 13 inches long) tries to update the LPX design. In these and other designs, additional components (such as video graphics, network interface card, modem, etc.) are integrated into the motherboard itself and further expansion is limited. Standard expansion cards are usually attached to a secondary riser card that is plugged into a special purpose motherboard slot.
Interface The latest motherboards have interface connectors built in so that installing the motherboard will fully emplace the connectors in the case. As mentioned before, parallel port, serial port, PS/2 keyboard, and PS/2 mouse connectors are now standard in ATX and later designs.
Depending upon the design, there can be up to two or four USB (universal serial bus) type-A connectors. However, after seeing piles of scorched USB cables for sale at swap meets (flea markets), I advise you to use a powered USB hub (with 500 milliamp hours of power per connection) when attaching high current USB devices to your computer. That way, you only jeopardize a $20 USB hub instead of a $120 motherboard.
Inexpensive digital still and video photography has prompted some designers to include support for IEEE1394 (also incorrectly known as Apple's FireWire), a digital high-speed serial bus. Recent IEEE1394 products include hard disk drives, CD-ROM/CD-R/CD-RW drives, flatbed scanners, etc.
Look for the fastest ATA (AT-Attachment) interface for your IDE (integrated drive electronics) drives. For now, they are Ultra ATA-33 (ultra DMA mode at 33 megabytes per second), Ultra ATA-66 (ultra DMA mode 4 at 66 megabytes per second), and Ultra ATA-100 (ultra DMA mode 5 at 100 megabytes per second). Needless to say, the next standard will likely be Ultra ATA-133.
Expansion Slots The most common method of adding electronic hardware to your computer will involve motherboard expansion slots. The preferred interface (except for video cards) is the PCI (peripheral component interface) bus slot. It is available in both 32 bit (that is designed for 133 megabytes per second) and 64 bit (that is designed for 266 megabytes per second) versions (commonly found on workstations and servers).
Avoid the antiquated ISA (industry standard architecture) bus slot since it was designed for extremely slow 2 to 8.33 megabytes per second performance. PCI devices are about 16 times faster.
The AGP (accelerated graphics port) bus slot is designed for 528 to 800 megabytes per second and faster, depending upon implementation. This is the best solution when high performance video is required.
Riser Cards Customers want a variety of features and manufacturers want to minimize production costs. To reach a compromise, a standardized motherboard is designed with a riser card slot. Now, the manufacturer creates a selection of riser cards to plug into this slot. Each card can contain a combination of one or more features such as audio, modem, and NIC (network interface card).
An older standard is the AMR (audio modem riser). The newest standard is the Intel CNR (communication and networking riser) for audio, modem, and LAN (local area network)
Memory and Chipset The chipset and microprocessor used determines the possible memory type and slot configurations. This is enough to require coverage in my next article entitled "Microprocessor Technology 2001."
Contact Information This article was originally published in the North Orange County Computer Club Orange Bytes newsmagazine for November 2001. Look for it on our award winning NOCCC Web site at http://www.noccc.org/. The latest version of this article can be found on my Web site at http://www.SingularityTechnology.com/articles/motherboardtech2001.html, assuming that I have time to create it... You can contact me, Herbert Wong Jr., at ocug@SingularityTechnology.com.
![[------STRIPE-----]](../../../cgif/str1.gif){kind=small}
Site Disclaimer Suggestions? E-Mail to webmaster@noccc.org