Motherboard Chipsets

by Kenny Bellew
March 2003

• Introduction
• What is a chipset?
• The North Bridge
• The South Bridge
• Chipset Manufacturers
  • VIA
  • SiS
  • nVidia (AMD only)
  • Intel
• Summary
• Intel Chipsets (Table)
• AMD Chipsets (Table)

Introduction

The goals and needs of today's computer hardware customer are more diverse than ever before.  Some people have a need for speed. Some will not buy a motherboard unless it has a list of specific features that he or she believes will be required for future upgrades. Others shy away from the cutting edge, instead requiring time-tested stability in a motherboard. Whether you are an over-clocker trying to squeeze the last MHz out of a CPU, or an IS manager who is looking for a corporate motherboard, you have to understand a motherboard's chipset.

This article will address popular chipsets for the most commonly used modern CPUs: Intel's Celeron and Pentium 4 and AMD's Duron and Athlon XP.

What is a chipset?

A motherboard chipset has both a general definition and a specific definition that varies by chipset manufacturer.  Generally speaking, a motherboard chipset controls the features and abilities of the motherboard.  If you understand which chipset a motherboard uses, you know a good deal about its potential features and abilities before ever reading the motherboard's specifications.

Modern motherboard chipsets nearly always consist of two separate chips. These two chips on the motherboard are called the north bridge and the south bridge. Together, the north bridge and the south bridge handle all of the communication between the processor, RAM, video options, PCI slots, BIOS, ATA controller, USB ports, integrated modem, integrated LAN port and integrated sound. The chipset also determines the type of RAM that can be used.

There are a dozen or so reputable motherboard manufacturers and about a half dozen popular chipset manufacturers.  Intel and AMD provide specifications to the chipset manufacturers, who, in turn, develop and sell chipsets with various features and abilities to motherboard manufacturers. Of course, the exceptions to this are Intel and AMD, who also create their own chipsets.

Figure 1: A = CPU slot, B = north bridge chip (covered by a cooling fan), C = south bridge chip	Figure 2: Intel 845PE chipset with 845PE north bridge chip (top) and the 82801DB south bridge chip

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The North Bridge

Front-Side Bus Speed

The north bridge controls the communication and throughput speed between AGP video, the RAM and the CPU.  The speed at  which the memory can communicate with the CPU is referred to as the front-side bus speed or system bus speed. For those who are looking for ultimate speed, the north bridge's front-side bus speed is a key item to study. If you want a fast CPU and fast RAM, you need a fast front-side bus.  Modern CPUs and RAM come in a variety of ratings for front-side bus speeds and must be matched with an appropriate chipset (which determines the motherboard's front-side bus speed). A speed mismatch will create a performance bottleneck.

For example, RAM can be purchased in a variety of speeds such as DDR200, DDR266, DDR333, or DDR400. Each number next to "DDR" represents a frequency speed rating. DDR266 should only be used with a front-side bus of at least 266MHz, and DDR400 requires at least a front-side bus speed of 400MHz. When the front-side bus speed is the same as the speed of the DDR RAM, this combination is described as being "synchronous." It is the motherboard chipset (within the north bridge) that specifies the front-side bus speed. See the glossary section for additional information on DDR speeds.

Sometimes a chipset will specify asynchronous combinations of front-side bus speed and RAM speed, such as allowing DDR400 to be used with a front-side bus speed of only 333MHz. Benefits from these asynchronous combinations usually require overclocking the front-side bus.

Modern Pentium 4 chipsets run at either 100MHz or 133MHz clock cycles. However, they are quad pumped (also known as quad data rate). Therefore, the front-side bus speeds are 400MHz or 533MHz.  To explain quad pumping - If a quad pumping 133MHz system bus were a car analogy, it would be analogous to taking a single 133MHz lane, and instead providing four 133MHz lanes of traffic.

AMD chipsets are similar, except that they operate at either 100MHz, 133MHz or 166MHz. AMD chipsets are double pumped (versus Intel's quad pumped). Therefore, the front-side bus operates at effective speeds of 200MHz, 266MHz or 333MHz respectively. However, do not be misled by the MHz rating of the chipset. While MHz is still important, it is no longer the sole determiner of system performance.

If we carry our car analogy further and compare MHz to horsepower, one car may have more horsepower but have a less efficient fuel system.  It is possible for a car that has a more efficient fuel system to run as fast as a car with more horsepower.  This is the case when comparing Pentium 4 and AMD chipsets. Intel's CPU and chipset runs at a higher total MHz than AMD's. However, AMD's CPU and chipset can run just as fast because it has higher efficiency (Specifically, In some scenarios, AMD is better at speculative branch predictions, which can increase the number of instructions per clock cycle).  This is the reason that AMD moved from identifying its processors by their megahertz rating to a name identified with a specific number.  The identifying number is meant to show that it is as fast as the corresponding Pentium 4. For example, the Althon XP 2700+ operates at 2166MHz; however, AMD asserts that it operates as fast as the Pentium 2.7GHz.

For more detailed information regarding front-side bus speeds, review Directron's article by Lee Penrod, "Understanding System Memory and CPU speeds: A layman's guide to the Front Side Bus (FSB)."

AGP Speed

Figure 3: Intel's 845E chipset diagram

The north bridge also controls the speed at which information is exchanged with the AGP video slot. In September of 2002, Intel released the final version of the AGP standard - AGP 3.0.  This moved the available speed of AGP video from 4X to 8X. AGP 8X can move data at twice the speed of AGP 4X.  While most people want fast AGP for gaming reasons, as of this writing (March 2003), there are no games available that can provide enough data to take advantage of AGP 8X. If you are deciding on which chipset to choose based on whether or not it supports AGP 8X, just understand that it may be a year or so before you will realize the fruits of this chipset capability.

Some north bridges have integrated graphics. In other words, you do not need to buy a separate video card. Video is built into the motherboard in the north bridge chipset.  This option is usually targeted toward the budget-conscious consumer who does not care whether or not a PC's graphics system can handle Unreal Tournament 2003. On the other hand, a few chipsets with integrated graphics have above average graphics-handling power, such as the nForce2 IGP chipset.

The South Bridge

The south bridge is often referred to as the I/O controller.  The features of the south bridge change less often than the those of the north bridge.  From chipset to chipset, nearly all south bridges have support for integrated sound, LAN and modem, ATA and USB. However, just because a chipset can support these features does not mean that the motherboard manufacturer will make that particular feature available. There are also some I/O components that are not controlled by current south bridges, such as RAID and Serial ATA. These have their own chips, separate from current north and south bridges. This will change in the future, as Intel is incorporating Serial ATA into their upcoming Springdale chipset.

When a chipset manufacturer releases a new chipset, it is common for the north bridge to change, while the south bridge may remain the same as the one used previously. There are two notable south-bridge controlled items that have changed over the last few generations of chipsets: USB 2.0 and ATA 133.

USB 2.0

USB 2.0 is forty times faster than USB 1.1, it is hardware dependent (the hardware must be USB 2.0 compatible) and it requires an operating system that supports it. For example, even if you are running Windows XP, you must have service pack one installed in order to utilize USB 2.0.  If you want USB 2.0, and you find a chipset you like that has everything except USB 2.0, you can always add a PCI card with USB 2.0 support fairly inexpensively.

Figure 4: Serial ATA cable

ATA 133

ATA is the IDE controller of the south bridge.  It controls your hard disk, CD/DVD drives, and any other IDE device. Modern chipsets all support ATA 100, and some support ATA 133.  The number after "ATA" represents, in theory, the amount of data in MB/second that can be transferred between your IDE device and the south bridge. Therefore, ATA 100 has a data throughput of 100MB/second and ATA 133 has a data throughput of 133MB/second.

ATA 133 is a standard that was developed by Maxtor in 2001. Maxtor holds the license for ATA 133, and they want to charge other hard disk manufacturers for the right to use this technology.  Currently, Maxtor is the only hard disk manufacturer that is producing hard disks with ATA 133 compatibilities. There are several reasons that other hard disk manufacturers have not adopted ATA 133. One reason is that Serial ATA hard disks are now becoming available. Serial ATA has a data throughput of 150MB/second.  Once Intel incorporates Serial ATA into its chipset, hard disk manufacturers will have even fewer reasons to license ATA133 from Maxtor.

Another reason is that data throughput speeds of the ATA 133 drives are being matched by ATA 100 hard disks with various configurations such as an 8MB cache.  Also, the additional 33% bandwidth of ATA 133 is more of a benefit when sudden bursts of data are required.  It quickly loses its efficiency over sustained transfers of data. 

ATA 133 used to have a capacity advantage over ATA100. The ATA 100 hard disks were limited to 137GB. However, in 2001, a standard was developed that allowed hard disks to utilize 48-bit logical block addressing. This removed the 137GB barrier to ATA100 hard disks. ATA hard disks with 48-bit addressing started appearing in 2002.

To summarize ATA 133, unless you have a very specific Maxtor hard disk you are looking to support, ATA 133 should not rank high on your chipset selection criteria list.

Audio Support in the South Bridge

Another way chipset manufacturers have differentiated their south bridge is by enhancing the audio support.  Most modern chipsets support six-channel audio (two front speakers, two rear surround channels, a center channel and a subwoofer).  The motherboard manufacturer may or may not provide six separate speaker connections, but the support is there for it in the chipset.  In addition, some chipset manufacturers, like nVidia, are incorporating AC3 (Dolby Digital) 5.1 encoding into the south bridge. 

Chipset Manufacturers

On the Pentium 4 side, the most popular chipset manufacturers are Intel, SiS and VIA. On the AMD side, the prominent chipset manufacturers are SiS, VIA, nVidia, AMD and ALi.

Earlier, it was mentioned that chipset manufacturers have their own specific way of naming and articulating the features of their chipsets.  Most chipset manufacturers will use the name of their north bridge as the name for the entire chipset, even though the south bridge has its own name. However, this is not always the case. For example, VIA's KT133A used a north bridge named VT8363A. Other chipset makers eschew the customary alphanumeric chipset name, and, instead, opt for a marketing name such as nForce. The north bridge usually gets the lime light; that is where the power lives. Advancing the features of the north bridge is what drives the release of a new chipset. In fact, it is not uncommon for a chipset to have its south bridge updated without changing the name of the chipset. For example, a chipset manufacturer may extend the life of a chipset by updating the south bridge to include ATA 133 and/or USB 2.0. 

Figure 5: CPU Market Share Early 2003

Not too long ago in the months between 2001 and mid 2002, the chipset market was dominated by VIA and Intel. However, recently, VIA has lost a dramatic amount of market share. SiS is now the second largest distributor of chipsets, with Intel still holding a dominant position distributing its own chipsets. For the various 3rd-party chipset manufacturers, market share is largely dependent on whether you develop chipsets for AMD, Intel or both.  Intel, however, can dominate the chipset market even though they do not develop AMD chipsets because, as of this writing, Intel has nearly 85% of the desktop, laptop and server market.  AMD has about  14% of total CPU market share (see Figure 4).

VIA

VIA has a long history of chipset development, and they have made fans and enemies along the way. A few years ago, VIA released a south bridge (686B) with PCI latency issues that caused havoc with sound cards, especially Creative Labs SoundBlaster cards (which were very popular cards at the time).  This gave VIA a bad name that lingers with some people, still long after the issue was resolved. All chipsets have hardware hiccups from time to time, and this was not VIA's last, but it continues to be very memorable to many.

Most recently, VIA has been wrestling with Intel over bus licensing rights that would allow them to advertise their 533MHz Pentium 4 chipset, P4X400, as supporting hyper-threading. VIA is claiming that Intel is using unfair competitive practices. This clash with Intel caused very few motherboard manufacturers to use the P4X400 initially. The licensing issue resolution has not been made public; however, VIA is now advertising hyper-threading support for the P4X400 chipset.  VIA's Pentium 4 chipset, P4X400, is very competitive, offering support for the 533MHz front-side bus, DDR400 and AGP 8X.

On the AMD side, the VIA KT400 has been a success.  The KT400 supports the fastest front-side bus possible for the AMD at 333MHz and AGP 8X, as well as the latest features in the south bridge, supporting USB 2.0 and ATA 133. However, VIA feels the pressure being presented by nVidia's nForce 2 line of chipsets that sport dual 64-bit memory controllers, allowing the use of dual-channel DDR configurations.  Recently (March 2003), VIA announced an update to the KT400 chipset, calling it the KT400A. 

The KT400A comes equipped with enhancements to the memory controller that VIA calls FastStream64?  This enhanced memory controller offers ten percent improvement in 3D applications over the previous KT400 chipset, and it officially supports DDR400.  It also offers native support for serial ATA when combined with the VT8237 south bridge.  If KT400A motherboards equipped with the VT8237 south bridge hit the streets before motherboards with Intel's Springdale chipset, they will be the first motherboards to support native serial ATA in the chipset.

Chipset manufacturers generally rely on motherboard manufacturers to provide direct technical support to end users. This is true for VIA as well. However, VIA does have a well-used forum for discussing chipset related problems called the VIA Arena. 

Figure 6: VIA's P4X400 Chipset Diagram	Figure 7: VIA's KT400 Chipset Diagram

SiS

SiS is aggressively pursuing the PC enthusiast market, and has just released a new chipset for the Pentium 4 called the SiS655. It  provides dual-channel DDR support, AGP 8X, USB 2.0 and integrated IEEE1394a.  Dual-channel DDR means that the north bridge memory controller will read from two DDR DIMMs at the same time, doubling (in theory) the maximum memory bandwidth capabilities. This chipset will compete with Intel's new E7205 chipset, which also supports dual-channel DDR.  However, the SiS655 chipset supports dual-channel DDR333, while Intel's E7205 only specifies DDR266 for dual-channel use.

SiS is often first on the chipset scene with new features and abilities. This time, they beat VIA to market for a dual-channel DDR solution. VIA will soon have the P4X600 chipset available to support dual-channel DDR.

SiS' latest AMD chipset is the SiS746FX. It supports 333MHz front-side bus, AGP 8X, USB 2.0 and ATA 133. One thing that is interesting about this release by SiS is that SiS is suggesting that you can use DDR400 with it. The following is from SiS' website: "The SiS 746FX DDR-400 memory controller delivering 3.2G/B bandwidth way adequate and satisfactory to the 333MHz S2K FSB bandwidth demand of 2.7 GB/s, absolutely brings out the best performance of each other, and still has a lot to spare for the multi-I/O masters, and AGP-8X masters."

Cutting through the hype and awkward sentences that are obviously composed by non-English speaking writers, a stock installation with a 333MHz front-side bus will not take full advantage of the bandwidth DDR400 has to offer.  However, the additional DDR bandwidth may appeal to those who like to overclock the front-side bus.

SiS' Latest Intel Chipset: SiS655

Figure 8: SiS655 north bridge for Pentium 4's	Figure 9: SiS963 South Bridge for SiS655

SiS' Latest AMD K7 Chipset: SiS647FX

Figure 10: SiS746FX Chipset Diagram

nVidia (AMD only)

nVidia has only been in the desktop chipset business for a couple of years, but they have quickly won a lot of enthusiastic fans in the AMD community. Being one of the most powerful names in desktop graphics, nVidia is no stranger to PC consumers. If you asked the average gaming enthusiast if he or she would like to have the same chipset in his or her computer that runs in Microsoft's Xbox, you would likely perk the gamer's attention. Of course, nVidia has had its chipset in the Xbox for over two years now.

nVidia's newest chipset for the desktop PC, the nForce2, offers motherboard manufactures a choice of four combinations for the north bridge and south bridge. The nForce2 builds on features of the original nForce chipset. The nForce2 has a choice of two north bridges: SPP and IGP. It also has two choices for the south bridge: MCP and MCP-T. These north and south bridges can be mixed and matched.

The main difference between the nForce2 SPP and the IGP is integrated graphics. SPP stands for Systems Platform Processor, and IGP stands for Integrated Graphics Processor. Both north bridges support dual-channel DDR with dual 64-bit memory controllers. Both support the option of AGP 8X. However, the IGP north bridge has an integrated GeForce 4 MX.

MCP stands for Media and Communications Processor. The MCP and MCP-T south bridges both offer ATA 133, USB 2.0, LAN and integrated audio. The MCP-T extends the features offering to include Dolby Digital 5.1 encoding, IEEE1394a and DualNet (two network controllers). The "T" in MCP-T stands for "Turbo", which refers to "more features" not "speed."

Currently, nVidia is only making chipsets for AMD CPU's. This probably suits Intel, SiS and VIA just fine, as nVidia is quickly capturing market share in the AMD community.  When nVidia approached Intel regarding developing chipsets for the Pentium 4, Intel's response was a licensing fee that made it very unattractive for nVidia.

An oddity that justifies mentioning is a slight naming convention difference for the nForce2 chipset from motherboard manufacturer to motherboard manufacturer. Some refer to the nForce2 south bridge as MCP and MCP-T and others use MCP2 and MCP2-T. For example, Abit and MSI refer to the nForce2 south bridge as MCP2 and MCP2-T. While Asus, EPoX, Chaintech, Leadtek, and Soltek call the nForce2 south bridge MCP and MCP-T. The reasoning for this is unclear; however, there are no differences within the nForce2 chipset that are identified by adding a "2" to the south bridge name. The danger is that someone might choose, for example, an MSI nForce2 MCP2-T motherboard over an Asus nForce2 MCP-T motherboard - thinking that the MCP2-T is more current or has more features than the MCP-T. This is not the case. It can further be confused by the fact the original nForce chipset referred to its south bridge as MCP and MCP-D. Of course, there is a difference between the nForce MCP and MCP-D and the nForce2 MCP and MCP-T.

Intel

Intel is still king of the chipset hill for market share.  For years, Intel has made a reputation of creating stable chipsets. Generally speaking, if you are looking for the ultimate in stability, you should investigate an Intel motherboard, which, of course, will have an Intel chipset. When you want the latest cutting-edge gaming features, like AGP 8X, you should see what is being offered by other chipset makers.  Intel's conservative approach can be illustrated by the fact that, even though there is a Intel chipset supporting AGP 8X (the E7205), there is not yet an Intel motherboard supporting AGP 8X (as of this writing).  Others, such as the motherboard manufacturer Gigabyte, have taken the Intel E7205 chipset and created the GA8INXP motherboard with AGP 8X. However, Intel has yet to release such a motherboard.

Saying Intel is conservative is not saying that their chipsets produce motherboards that are performance slouches. In fact, if you research which Pentium 4 motherboards are best for overclocking, you will usually find a 3rd-party manufacturer, such as Abit and Asus, using an Intel chipset.

Intel's latest desktop motherboard chipset is the 845PE, which supports a 533MHz front-side bus, Hyper-Threading, AGP 4X and DDR333. Its south bridge supports the usual south bridge inclusions and USB 2.0 and ATA 100.  All of the Intel chipsets with a 533MHz front-side bus support hyper-threading.

Figure 12: Intel 845PE north bridge and 82801DB south bridge	Figure 13: Intel 845PE chipset diagram

Intel's E7205 is technically designated as a workstation chipset. However, gaming enthusiast and those in search of the fastest desktop system with an Intel chipset are happily using E7205 motherboards, such as the GA8INXP motherboard, in home systems. So, in that sense, you could say that the E7205 is actually the latest Intel desktop chipset.

One of the most exciting things about the E7205 is that it supports dual-channel DDR. However, the fastest RAM supported by the chipset is DDR266. Later this year, Intel will release the Springdale chipset that will support dual-channel DDR400 with an 800MHz front-side bus.

Summary

It is important to realize that chipsets are not like your motherboard BIOS, which can be updated to add features. Chipsets are not like a CPU chip, which can be removed and changed. Chipsets cannot be updated without replacing the motherboard. You need to understand the features and capabilities of a motherboard's chipset to make sure that your goals are going to be met. If you are on a budget, you might look for a chipset that has integrated graphics in the north bridge and integrated sound, modem and LAN in the south bridge.  If you are looking for a gaming screamer, you need to understand the supported front-side bus speed and whether or not AGP 8X is important to you.

Study the chipset matrixes at the bottom of this article to see differences at a glance.