Motherboard Category

A comprehensive glossary of motherboard related terms


  • Voltage Regulator Module: used to absorb the voltage difference between a CPU which may be added in the future and the motherboard.


  • VESA Local Bus or VL-Bus: the 32-bit local-bus standard created by the Video Electronics Standards Association (VESA) to provide a fast data connection between CPUs and local-bus devices. The VL-Bus was widely used in 486 PCs, but has since been replaced by the Intel PCI Bus.

Ultra DMA

A hard drive protocol which doubled the previous maximum I/O throughput to 33 MBps.

System Bus

  • The primary pathway between the CPU, memory and high-speed peripherals to which expansion buses, such as ISA, EISA, PCI and VL-Bus, can connect. Also referred to as the external bus or host bus, and came to be used interchangeably with frontside bus (FSB) following the introduction of Intel’s Dual Independent Bus (DIB) architecture in 1997.


  • Refers to the Peripheral Bus Controller component of a Pentium chipset, responsible for implementing a PCI-to-ISA bridge function and for managing the ISA bus and all the ports. See also Northbridge.

Socket A

  • AMD’s 462-pin CPU interface form factor which replaced Slot A at the time of the introduction of the Thunderbird and Spitfire cores used by AMD’s Athlon and Duron desktop processor ranges respectively.

Socket 7

  • The CPU interface form factor for fifth-generation Pentium-class CPU chips from Intel, Cyrix, and AMD.

Socket 8

  • Intel’s proprietary CPU interface form factor used exclusively by their sixth-generation Pentium Pro CPU chip. Socket 8 is a 387-pin ZIF socket with connections for the CPU and one or two SRAM dies for the Level 2 cache.

Socket 478

  • Intel’s proprietary CPU interface form factor which replaced Socket 423 with the advent of the 0.13-micron Pentium 4 Northwood core.

Socket 423

  • Intel’s proprietary CPU interface form factor used by its early Pentium 4 processors.

Socket 370

  • Intel’s proprietary CPU interface form factor first introduced for its Celeron line of CPUs and subsequently adopted for later versions of the Pentium III family.

Slot A

  • AMD’s proprietary 242-way connector SEC cartridge used by their original Athlon processor. Physically identical to Slot 1 but electrically incompatible.

Slot 2

  • An enhanced Slot 1, which uses a somewhat wider 330-way connector SEC cartridge that holds up to four processors. The biggest difference from Slot 1 is that the Level 2 runs at full processor speed.

Slot 1

  • Intel’s proprietary CPU interface form factor for Pentium II CPUs. Slot 1 replaces the Socket 7 and Socket 8 form factors used by previous Pentium processors. It is a 242-contact daughtercard slot that accepts a microprocessor packaged as a Single Edge Contact (SEC) cartridge. Communication between the Level 2 cache and CPU is at half the CPU’s clock speed.


  • Small Computer System Interface: an American National Standards Institute (ANSI) interface between the computer and peripheral controllers. SCSI excels at handling large hard disks and permits up to eight devices to be connected along a single bus provided by a SCSI connection. The original 1986 SCSI-1 standard is now obsolete and references to “SCSI” generally refer to the “SCSI-2” variant. Also features in Narrow, Wide and UltraWide flavours. See also IDE.

RAS Line

  • Physical track on motherboard used to select which sides of which SIMMs will be involved in a data transfer. A given chipset supports only a certain number of RAS lines, thereby dictating how many SIMMs can be accommodated. A pair of SIMMs uses one RAS line; a pair of DIMMs uses two.


  • Power-On Self-Test: a set of diagnostic routines that run when a computer is first turned on.


  • PCI ISA IDE Xcelerator: a key component of the Peripheral Bus Controller chipset, responsible for integrating many common I/O functions found in ISA-based PC systems.


  • Mode Programmed Input Output Mode: a method of transferring data to and from a storage device (hard disk or CD device) controller to memory via the computer’s I/O ports, where the CPU plays a pivotal role in managing the throughput. For optimal performance a controller should support the drive’s highest PIO mode (usually PIO mode 4).


  • Peripheral Component Interface: the 32-bit bus architecture (64-bit with multiplexing), developed by DEC, IBM, Intel, and others, that is widely used in Pentium-based PCs. A PCI bus provides a high-bandwidth data channel between system board components such as the CPU and devices such as hard disks and video adapters. Superseded the VL-Bus, which was widely used in 486 PCs in the early 1990s.


  • Refers to the System Controller component of a Pentium chipset, responsible for integrating the cache and main memory DRAM control functions and for managing the host and PCI buses. See also Southbridge.


  • An Intel-designed motherboard form factor. It features a number of improvements over the ATX design providing support for new technologies such as AGP and allows easier access to motherboard components.


  • The PC’s main printed circuit board which houses the processor, memory and other components.


  • Micro Channel Architecture: a 32-bit bus architecture introduced by IBM for their PS/2 series microcomputers. Incompatible with original PC/AT (ISA) architecture.


  • A motherboard form factor which allows for smaller cases used in some desktop model PCs. The distinguishing characteristic of LPX is that expansion boards are inserted into a riser that contains several slots and are therefore parallel, rather than perpendicular, to the motherboard.

Local Bus

  • A bus which co-exists with the main bus and connects the processor itself to the main memory. PCI is now the standard local bus architecture, having replaced the older VL-Bus.


  • Small metal blocks with black plastic handles for enabling or disabling specific functions on a motherboard or expansion card.


  • Industry Standard Architecture: the architectural standard for the IBM XT (8-bit) and the IBM AT (16-bit) bus designs. In ISA systems, an adapter added by plugging the card into one of the 16-bit expansion slots enables expansion devices like network cards, video adapters and modems to send data to and receive data from the PC’s CPU and memory 16 bits at a time. See also EISA.


  • Interrupt ReQuest: a signal generated by a device to request processing time from the CPU. Each time a keyboard button is pressed or a character is printed to a screen, an IRQ is generated by the requesting device. IRQ signals are transmitted along IRQ lines, which connect peripheral devices to a programmable interrupt controller, or PIC. A PC has 16 IRQs, and no two operational devices can share the same IRQ.


  • Integrated Device Electronics or Intelligent Drive Electronics: a drive-interface specification for small to medium-size hard disks (disks with capacities up to 504Mb) in which all the drive’s control electronics are part of the drive itself, rather than on a separate adapter connecting the drive to the expansion bus. This high level of integration shortens the signal paths between drives and controllers, permitting higher data transfer rates and simplifying adapter cards. See also EIDE and SCSI.

Host Adapter

  • A plug-in board or circuitry on the motherboard that acts as the interface between the system bus and a peripheral device. IDE and SCSI are examples of peripheral interfaces that call their controllers host adapters.

Heat Sink

  • A structure, attached to or part of a semiconductor device that serves the purpose of dissipating heat to the surrounding environment; usually metallic and often aluminium.

Frontside Bus

  • The bus within a microprocessor that connects the CPU with main memory. See also Backside Bus.


  • The interface which allows a floppy or tape drive to be connected to the motherboard.

Expansion Bus

  • An input/output bus typically comprised of a series of slots on the motherboard. Expansion boards are plugged into the bus. ISA, EISA, PCI and VL-Bus are examples of expansion buses used in a PC.


  • Region of non-volatile memory used by BIOS and ICU (Intel Configuration Utility) or PnP operating system to record information about the current configuration of the system.


  • Enhanced Small Device Interface: an interface standard developed by a consortium of the leading PC manufacturers for connecting disk drives to PCs. Introduced in the early 1980s, ESDI was two to three times faster than the older ST-506 standard. It has long since been superseded by the IDE, EIDE and SCSI interfaces.


  • Extended Industry Standard Architecture: an open 32-bit extension to the ISA 16-bit bus standard designed by Compaq, AST and other clone makers in response to IBM’s proprietary MCA (Micro Channel Architecture) 32-bit bus design. Unlike the Micro Channel, an EISA bus is backward-compatible with 8-bit and 16-bit expansion cards designed for the ISA bus.


  • Enhanced Integrated Device Electronics or Enhanced Intelligent Drive Electronics: an enhanced version of the IDE drive interface that expands the maximum disk size from 504Mb to 8.4Gb, more than doubles the maximum data transfer rate, and supports up to four drives per PC (as opposed to two in IDE systems). EIDE’s primary competitor is SCSI-2, which also supports large hard disks and high transfer rates.

Dynamic Power Management Architecture – DPMA

  • Intel’s extensive set of power management features built in at the chipset level, with particular emphasis on intelligent power conservation and standby facilities.


  • Direct Memory Access: a process by which data moves directly between a disk drive (or other device) and system memory without requiring the involvement of the CPU, thus allowing the system to continue processing other tasks while the new data is being retrieved.

DIP Switch

  • Switch mounted on PC board for configuration options.

Concurrent PCI

  • An enhancement to the PCI bus architecture that allows PCI and ISA buses to transfer data simultaneously.

Communications and Networking Riser – CNR

  • An Intel riser card architecture that provides expanded audio, modem and networking functions.


  • Complementary Metal Oxide Semiconductor Random Access Memory: a bank of memory that stores a PC’s permanent configuration information, including type identifiers for the drives installed in the PC, and the amount of RAM present. It also maintains the correct date, time and hard drive information for the system.


  • A number of integrated circuits designed to perform one or more related functions.


  • An intermediate storage capacity between the processor and the RAM or disk drive. The most commonly used instructions are held here, allowing for faster processing.

Bus Master IDE

  • Capability of the PIIX element of Triton chipset to effect data transfers from disk to memory with minimum intervention by the CPU, saving its horsepower for other tasks.


  • Basic Input Output System: a set of low-level routines in a computer’s ROM that application programs (and operating systems) can use to read characters from the keyboard, output characters to printers, and interact with the hardware in other ways. It also provides the initial instructions for POST (Power On Self-Test) and booting the system files.

Baby AT

  • The form factor used by most PC motherboards in the early 1990s. The original motherboard for the PC-AT measured 12in by 13in. Baby AT motherboards are a little smaller, 8.5in by 11in.


  • The predominant motherboard form factor since the mid-1990s. It improves on the previous standard, the Baby AT form factor, by rotating the orientation of the board 90 degrees. This allows for a more efficient design, with disk drive cable connectors nearer to the drive bays and the CPU closer to the power supply and cooling fan.


  • Advanced Technology Packet Interface: a specification that defines device side characteristics for an IDE connected peripheral, such as CD-ROM or tape drives. ATAPI is essentially an adaptation of the SCSI command set to the IDE interface.


  • AT Attachment: the specification, formulated in the 1980s by a consortium of hardware and software manufacturers, that defines the IDE drive interface. AT refers to the IBM PC/AT personal computer and its bus architecture. IDE drives are sometimes referred to as ATA drives or AT bus drives. The newer ATA-2 specification defines the EIDE interface, which improves upon the IDE standard. See also IDE and EIDE.

AT Bus

  • The 16-bit bus started with the IBM-AT (Advanced Technology) systems. It is still the standard interface for most PC expansion cards. It is also known as the ISA (Industry Standard Architecture) bus.


  • Audio Modem Riser: an Intel specification that defines a new architecture for the design of motherboards. AMR allows manufacturers create motherboards without analogue I/O functions. Instead, these functions are placed on a separate card which plugs in perpendicular to the motherboard so that the motherboard and “riser” card form a right angle.


  • Accelerated Graphics Port: an Intel-designed 32-bit PC bus architecture introduced in 1997 allowing graphics cards direct access to the system bus (currently up to 100MHz), rather than going through the slower 33MHz PCI bus. AGP uses a combination of frame buffer memory local to the graphics controller, as well as system memory, for graphics data storage, vastly increasing the amount of memory available for 3D textures.

Advanced Communication Riser – ACR

  • A rival riser card architecture to Intel’s CNR specification, which emerged at about the same time and offers similar features.


  • Advanced Configuration and Power Interface: the successor to DPMA for controlling power management and monitoring the health of the system.


  • Zero Insertion Force: a socket allows a processor to be upgraded easily and without the need for specialist tools. It clamps down on the microprocessor pins using a small lever located to the side of the socket. Socket 5 and Socket 7 are common types of ZIF socket.


  • Land Grid Array 775: Intel’s proprietary CPU interface form factor introduced in the summer of 2004. Similar to a pin grid array (PGA), the connection between LGA775 chip packaging and the processor chip is via an array of solder bumps rather than pins. Also referred to as Socket T.

Socket 754

  • AMD’s 754-pin CPU interface form factor introduced with its 64-bit Athlon 64 processor in the autumn of 2003.


  • Balanced Technology Extended: Intel’s interface specification developed as an evolutionary follow-on to the ATX form factor and designed to better accommodate modern-day PC technologies and lead to cooler, quieter, and more efficient PCs of all sizes.


  • PCI Express; a version of the PCI computer bus that uses existing PCI programming concepts, but bases it on a completely different and much faster serial physical-layer communications protocol. While the original was a single parallel data bus that operated at 33MHz with a peak theoretical bandwidth of 132MBps, PCIe is a two-way serial connection that carries data in packets along two pairs of point-to-point data lanes. The first generation of PCIe architecture provided up to 8GBps of dedicated bi-directional bandwidth.

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