
In computing, a northbridge (also host bridge, or memory controller hub) is a
microchip
An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
that comprises the core logic
chipset
In a computer system, a chipset is a set of electronic components on one or more integrated circuits that manages the data flow between the processor, memory and peripherals. The chipset is usually found on the motherboard of computers. Chips ...
architecture on
motherboard
A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see #Nomenclature, "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It ho ...
s to handle high-performance tasks, especially for older
personal computer
A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...
s. It is connected directly to a
CPU via the
front-side bus (FSB), and is usually used in conjunction with a slower
southbridge to manage communication between the
CPU and other parts of the motherboard.
Historically, separation of functions between CPU, northbridge, and southbridge chips was necessary due to the difficulty of integrating all components onto a single
chip die. However, as CPU speeds increased over time, a
bottleneck
Bottleneck may refer to:
* the narrowed portion (neck) of a bottle
Science and technology
* Bottleneck (engineering), where the performance of an entire system is limited by a single component
* Bottleneck (network), in a communication network
* ...
emerged due to limitations caused by
data transmission
Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...
between the CPU and its support chipset. The trend for integrated northbridges began near the end of the 2000s for example, the
Nvidia GeForce 320M GPU in the 2010 MacBook Air was a northbridge/southbridge/GPU combo chip.
On older Intel based PCs, the northbridge was also named external memory controller hub or graphics and memory controller hub if equipped with integrated graphics. Increasingly these functions became integrated into the CPU chip itself,
beginning with memory and graphics controllers. Since the 2010s,
die shrink
The term die shrink (sometimes optical shrink or process shrink) refers to the List of semiconductor scale examples, scaling of metal–oxide–semiconductor (MOS) devices. The act of shrinking a Die (integrated circuit), die creates a somewhat ...
and improved
transistor density have allowed for increasing chipset integration, and the functions performed by northbridges are now often incorporated into other components such as southbridges or CPUs themselves.
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...
and
AMD
Advanced Micro Devices, Inc. (AMD) is an American multinational corporation and technology company headquartered in Santa Clara, California and maintains significant operations in Austin, Texas. AMD is a hardware and fabless company that de ...
have both released chipsets in which all northbridge functions had been integrated into the CPU.
The corresponding southbridge was renamed by Intel as the
Platform Controller Hub and by AMD as the
Fusion controller hub
This is an overview of chipsets sold under the AMD brand, manufactured before May 2004 by the company itself, before the adoption of open platform approach as well as chipsets manufactured by ATI Technologies after October 2006 as the completion ...
. AMD FX CPUs continued to require external northbridge and southbridge chips. Modern Intel Core processors have the northbridge integrated on the CPU die, where it is known as the
uncore or system agent.
Overview
The northbridge typically handles communications among the
CPU, in some cases
RAM, and
PCI Express
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed standard used to connect hardware components inside computers. It is designed to replace older expansion bus standards such as Peripher ...
(or
AGP) video cards, and the
southbridge. Some northbridges also contain integrated video controllers, also known as a Graphics and Memory Controller Hub in Intel systems. Because different processors and RAM require different signaling, a given northbridge will typically work with only one or two classes of CPUs and generally only one type of RAM.
There are a few chipsets that support two types of RAM; generally, these are made available when there is a shift to a new standard. For example, the northbridge from the 2002
Nvidia
Nvidia Corporation ( ) is an American multinational corporation and technology company headquartered in Santa Clara, California, and incorporated in Delaware. Founded in 1993 by Jensen Huang (president and CEO), Chris Malachowsky, and Curti ...
nForce2 chipset only worked with
Socket A processors combined with
DDR SDRAM
Double Data Rate Synchronous Dynamic Random-Access Memory (DDR SDRAM) is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) class of memory integrated circuits used in computers. DDR SDRAM, also retroactively called DDR ...
.
PowerPC
Northbridge chips are most commonly found on X86-based PCs, but they can also be found on other platforms, such as the
PowerPC
PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...
platform. A common example of a northbridge on a PowerPC platform is in Apple's older PowerPC-based computers like the
iMac G5, which utilized an IBM CPC945 Northbridge chip. According to an Apple Developer note, The
Power Mac G5
The Power Mac G5 is a series of personal computers designed, manufactured, and sold by Apple Computer, Inc. from 2003 to 2006 as part of the Power Mac series. When introduced, it was the most powerful computer in Apple's Macintosh lineup, a ...
's northbridge chip connected to a "Mid Bridge", which then connected to a south bridge.
Etymology
The name is derived from drawing the architecture in the fashion of a map. The CPU would be at the top of the map comparable to due north on most general purpose geographical maps. The CPU would be connected to the
chipset
In a computer system, a chipset is a set of electronic components on one or more integrated circuits that manages the data flow between the processor, memory and peripherals. The chipset is usually found on the motherboard of computers. Chips ...
via a fast bridge (the northbridge) located north of other system devices as drawn. The northbridge would then be connected to the rest of the chipset via a slow bridge (the southbridge) located south of other system devices as drawn.
Overclocking
The northbridge plays an important part in how far a computer can be
overclocked, as its frequency is commonly used as a baseline for the CPU to establish its own operating frequency. This chip typically gets hotter as processor speed becomes faster, requiring more cooling. There is a limit to CPU overclocking, as
digital circuit
In theoretical computer science, a circuit is a model of computation in which input values proceed through a sequence of gates, each of which computes a function. Circuits of this kind provide a generalization of Boolean circuits and a mathematica ...
s are limited by physical factors such as rise, fall, delay and storage times of the
transistors
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
, current gain bandwidth product,
parasitic capacitance
Parasitic capacitance or stray capacitance is the unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors a ...
, and
propagation delay
Propagation delay is the time duration taken for a signal to reach its destination, for example in the electromagnetic field, a wire, speed of sound, gas, fluid or seismic wave, solid body.
Physics
* An electromagnetic wave travelling through ...
, which increases with (among other factors)
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
; consequently most overclocking applications have software-imposed limits on the
multiplier and external clock setting. Additionally, heat is a major limiting factor, as higher voltages are needed to properly activate
field effect transistors inside CPUs and this higher voltage produces larger amounts of heat, requiring greater thermal solutions on the die.
Evolution

The overall trend in processor design has been to integrate more functions onto fewer components, which decreases overall motherboard cost and improves performance. The
memory controller
A memory controller, also known as memory chip controller (MCC) or a memory controller unit (MCU), is a digital circuit that manages the flow of data going to and from a computer's main memory. When a memory controller is integrated into anothe ...
, which handles communication between the CPU and RAM, was moved onto the processor
die by AMD beginning with their
AMD K8 processors and by Intel with their
Nehalem processors. One of the advantages of having the memory controller integrated on the CPU die is to reduce latency from the CPU to memory.
Some northbridge chips have supported dual processors, for example Intel's 5000X memory controller used in the original
Mac Pro
Mac Pro is a series of workstations and servers for professionals made by Apple Inc. since 2006. The Mac Pro, by some performance benchmarks, is the most powerful computer that Apple offers. It is one of four desktop computers in the current ...
from 2006.
Another example of this kind of change is
Nvidia
Nvidia Corporation ( ) is an American multinational corporation and technology company headquartered in Santa Clara, California, and incorporated in Delaware. Founded in 1993 by Jensen Huang (president and CEO), Chris Malachowsky, and Curti ...
's
nForce3 for
AMD K8 systems. It combines all of the features of a normal
southbridge with an
Accelerated Graphics Port
Accelerated Graphics Port (AGP) is a parallel expansion card standard, designed for attaching a video card to a computer system to assist in the acceleration of 3D computer graphics. It was originally designed as a successor to PCI-type connec ...
(AGP) port and connects directly to the CPU. On
nForce4 boards it was marketed as a media communications processor (MCP).
AMD Accelerated Processing Unit
AMD Accelerated Processing Unit (APU), formerly known as Fusion, is a series of 64-bit microprocessors from Advanced Micro Devices (AMD), combining a general-purpose AMD64 central processing unit ( CPU) and 3D integrated graphics processing un ...
processors feature full integration of northbridge functions onto the CPU chip or package, along with processor cores, memory controller, high speed
PCI Express
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed standard used to connect hardware components inside computers. It is designed to replace older expansion bus standards such as Peripher ...
interface (usually for graphics card), and integrated graphics processing unit (
iGPU
A graphics card (also called a video card, display card, graphics accelerator, graphics adapter, VGA card/VGA, video adapter, display adapter, or colloquially GPU) is a computer expansion card that generates a feed of graphics output to a displa ...
). This was an evolution of the AMD K8, since the memory controller was integrated on the CPU die in the AMD64.
The northbridge was replaced by the system agent introduced by the Intel
Sandy Bridge
Sandy Bridge is the List of Intel codenames, codename for Intel's 32 nm process, 32 nm microarchitecture used in the second generation of the Intel Core, Intel Core processors (Intel Core i7, Core i7, Intel Core i5, i5, Intel Core i3, i3). The Sa ...
microarchitecture in 2011, which essentially handles all previous Northbridge functions. Intel's Sandy Bridge processors feature full integration of northbridge functions onto the CPU chip, along with processor cores, memory controller, high speed PCI Express interface and integrated
graphics processing unit
A graphics processing unit (GPU) is a specialized electronic circuit designed for digital image processing and to accelerate computer graphics, being present either as a discrete video card or embedded on motherboards, mobile phones, personal ...
(GPU). This was a further evolution of the Westmere architecture, which also featured a CPU and GPU
in the same package.
Recent AMD processors starting with the
Zen 2 have moved some I/O functions out of the CPU die onto an I/O die on the same
MCM package as the CPU. This die is not normally considered to be part of the Northbridge, since it is in the same package as the CPU, but it serves some of the same functions.
See also
*
Intel Management Engine (ME)
References
{{Reflist
IBM PC compatibles
Chipsets