Chipsets
We can't talk about modern
motherboards without discussing chipsets. The chipset is
the motherboard; therefore, any two boards with the same chipsets are
functionally identical. The chipset contains the processor bus interface
(called front-side bus, or FSB), memory controllers, bus controllers, I/O
controllers, and more. All the circuits of the motherboard are contained within
the chipset. If the processor in your PC is like the engine in your car, the
chipset represents the chassis. It is the framework in which the engine rests
and is its connection to the outside world. The chipset is the frame,
suspension, steering, wheels and tires, transmission, driveshaft, differential,
and brakes. The chassis in your car is what gets the power to the ground,
allowing the vehicle to start, stop, and corner. In the PC, the chipset
represents the connection between the processor and everything else. The
processor can't talk to the memory, adapter boards, devices, and so on without
going through the chipset. The chipset is the main hub and central nervous
system of the PC. If you think of the processor as the brain, the chipset is
the spine and central nervous system.
Because the chipset controls
the interface or connections between the processor and everything else, the
chipset ends up dictating which type of processor you have; how fast it will
run; how fast the buses will run; the speed, type, and amount of memory you can
use; and more. In fact, the chipset might be the single most important
component in your system, possibly even more important than the processor. I've
seen systems with faster processors be outperformed by systems with slower
processor but a better chipset, much like how a car with less power might win a
race through better cornering and braking. When deciding on a system, I start
by choosing the chipset first because the chipset decision then dictates the
processor, memory, I/O, and expansion capabilities.
Chipset Evolution
When IBM created the first PC
motherboards, it used several discrete (separate) chips to complete the design.
Besides the processor and optional math coprocessor, many other components were
required to complete the system. These other components included items such as
the clock generator, bus controller, system timer, interrupt and DMA
controllers, CMOS RAM and clock, and keyboard controller. Additionally, many
other simple logic chips were used to complete the entire motherboard circuit,
plus, of course, things such as the actual processor, math coprocessor
(floating-point unit), memory, and other parts. Table lists all the primary
chip components used on the original PC/XT and AT motherboards.
In addition to the
processor/coprocessor, a six-chip set was used to implement the primary
motherboard circuit in the original PC and XT systems. IBM later upgraded this
to a nine-chip design in the AT and later systems, mainly by adding more
interrupt and DMA controller chips and the nonvolatile CMOS RAM/Real-time Clock
chip. All these motherboard chip components came from Intel or an
Intel-licensed manufacturer, except the CMOS/Clock chip, which came from
Motorola. To build a clone or copy of one of these IBM systems required all
these chips plus many smaller discrete logic chips to glue the design together,
totaling 100 or more individual chips. This kept the price of a motherboard
high and left little room on the board to integrate other functions.
In 1986, a company called
Chips and Technologies introduced a revolutionary component called the
82C206—the main part of the first PC motherboard chipset. This was a
single chip that integrated into it all the functions of the main motherboard
chips in an AT-compatible system. This chip included the functions of the 82284
Clock Generator, 82288 Bus Controller, 8254 System Timer, dual 8259 Interrupt
Controllers, dual 8237 DMA Controllers, and even the MC146818 CMOS/Clock chip.
Besides the processor, virtually all the major chip components on a PC
motherboard could now be replaced by a single chip. Four other chips augmented
the 82C206 acting as buffers and memory controllers, thus completing virtually
the entire motherboard circuit with five total chips. This first chipset was
called the CS8220 chipset by Chips and Technologies. Needless to say, this was
a revolutionary concept in PC motherboard manufacturing. Not only did it
greatly reduce the cost of building a PC motherboard, but it also made
designing a motherboard much easier. The reduced component count meant the
boards had more room for integrating other items formerly found on expansion
cards. Later, the four chips augmenting the 82C206 were replaced by a new set
of only three chips, and the entire set was called the New Enhanced AT (NEAT)
CS8221 chipset. This was later followed by the 82C836 Single Chip AT (SCAT)
chipset, which finally condensed all the chips in the set down to a single
chip.
The chipset idea was rapidly
copied by other chip manufacturers. Companies such as Acer, Erso,
Opti, Suntac, Symphony,
UMC, and VLSI each gained an important share of this market. Unfortunately for
many of them, the chipset market has been a volatile one, and many of them have
long since gone out of business. In 1993, VLSI had become the dominant force in
the chipset market and had the vast majority of the market share; by the next
year, VLSI (which later was merged into Philips Semiconductors), along with
virtually everybody else in the chipset market, was fighting to stay alive.
This is because a new chipset manufacturer had come on the scene, and within a
year or so of getting serious, it was totally dominating the chipset market.
That company was Intel, and after 1994, it had a virtual lock on the chipset
market. If you have a motherboard built since 1994 that uses or accepts an
Intel processor, chances are good that it has an Intel chipset on it as well.
More recently, Intel has
struggled somewhat with chipsets because of its reliance on RDRAM memory. Intel
originally signed a contract with Rambus back in 1996
declaring it would support this memory as its primary focus for desktop PC
chipsets through 2001. I suspect this has turned out to be something Intel
regrets (the contract has since expired). RDRAM memory has had a significantly
higher price than SDRAM memory—although the
prices have recently come down a bit—and it does
have some performance advantages when used in a dual-channel mode. There is a
lot of momentum in the market for supporting double data rate (DDR) SDRAM.
Consequently, Intel introduced the 845 chipset (code named Brookdale),
which supports DDR-SDRAM with the Pentium 4. Intel's latest chipsets for
Pentium 4, the i865 (code named
Although AMD has developed its
own chipsets for the K6 and Athlon family of
processors, it now emphasizes encouraging third-party chipset developers to
support its products. Today, VIA Technologies is the leading developer of AMD Athlon/Athlon XP/Duron chipsets
for both discrete and integrated uses. The popularity of AMD processors has
also encouraged SiS, ATI, NVIDIA, and ALi Corporation to develop chipsets for both Intel- and
AMD-based systems.
It is interesting to note that
the original PC chipset maker, Chips and Technologies, survived by changing
course to design and manufacture video chips and found a niche in that market
specifically for laptop and notebook video chipsets. Chips and Technologies was subsequently bought out by Intel in 1998 as a part of
Intel's video strategy.
Intel Chipsets
You can't talk about chipsets
today without discussing Intel because it currently owns the vast majority of
the chipset market. It is interesting to note that we probably have Compaq to
thank for forcing Intel into the chipset business in the first place!
The thing that really started
it all was the introduction of the EISA bus designed by Compaq in 1989. At that
time, it had shared the bus with other manufacturers in an attempt to make it a
market standard. However, Compaq refused to share its EISA bus chipset—a set of custom chips necessary to implement
this bus on a motherboard.
Enter Intel, who decided to fill
the chipset void for the rest of the PC manufacturers wanting to build EISA bus
motherboards. As is well known today, the EISA bus failed to become a market
success except for a short-term niche server business, but Intel now had a
taste of the chipset business and this it apparently wouldn't forget. With the
introduction of the 286 and 386 processors, Intel became impatient with how
long it took the other chipset companies to create chipsets around its new
processor designs; this delayed the introduction of motherboards that supported
the new processors. For example, it took more than two years after the 286
processor was introduced for the first 286 motherboards to appear and just over
a year for the first 386 motherboards to appear after the 386 had been
introduced. Intel couldn't sell its processors in volume until other
manufacturers made motherboards that would support them, so it thought that by
developing motherboard chipsets for a new processor in parallel with the new
processor, it could jumpstart the motherboard business by providing ready-made
chipsets for the motherboard manufacturers to use.
Intel tested this by
introducing the 420 series chipsets along with its 486 processor in April 1989.
This enabled the motherboard companies to get busy right away, and in only a
few months the first 486 motherboards appeared. Of course, the other chipset
manufacturers weren't happy; now they had Intel as a competitor, and Intel
would always have chipsets for new processors on the market first!
Intel then realized that it
made both processors and chipsets, which were
90% of the components on a typical motherboard. What better way to ensure that
motherboards were available for its Pentium processor when it was introduced
than by making its own motherboards as well and having these boards ready on
the new processor's introduction date. When the first Pentium processor debuted
in 1993, Intel also debuted the 430LX chipset as well
as a fully finished motherboard. Now, besides the chipset companies being
upset, the motherboard companies weren't too happy, either. Intel was not only
the major supplier of parts needed to build finished boards (processors and
chipsets), but was now building and selling the finished boards as well. By
1994, Intel dominated the processor and chipset markets and had cornered the
motherboard market as well.
Now as Intel develops new
processors, it develops chipsets and motherboards simultaneously, which means
they can be announced and shipped in unison. This eliminates the delay between
introducing new processors and waiting for motherboards and systems capable of
using them, which was common in the industry's early days. For the consumer,
this means no waiting for new systems. Since the original Pentium processor in
1993, we have been able to purchase ready-made systems on the same day a new
processor is released.
In my seminars, I ask how many
people in the class have Intel-brand PCs. Of course, Intel does not sell or
market a PC under its own name, so nobody thinks they have an "Intel-brand"
PC. But, if your motherboard was made by Intel, for all intents and purposes
you sure seem to have an Intel-brand PC, at least as far as the components are
concerned. Does it really matter whether Dell, Gateway, or Micron put that same
Intel motherboard into a slightly different looking case with their name on it?
If you look under the covers,
you'll find that many, if not most, of the systems from the major manufacturers
are really the same because they basically use the same parts. Although more
and more major manufacturers are offering AMD Athlon-
and Duron-based systems as alternatives to Intel's,
no manufacturer dominates AMD motherboard sales the way Intel has dominated OEM
sales to major system manufacturers.
To hold down pricing, many
low-cost retail systems based on micro-ATX motherboards use non-Intel
motherboards (albeit with Intel chipsets in most cases). But, even though many
companies make Intel-compatible motherboards for aftermarket upgrades or local
computer assemblers, Intel still dominates the major vendor OEM market for
midrange and high-end systems.
Intel Chipset
Model Numbers
Starting with the 486 in 1989,
Intel began a pattern of numbering its chipsets as follows:
|
Chipset
Number |
Processor
Family |
|
420xx |
P4 (486) |
|
430xx |
P5 (Pentium) |
|
440xx |
P6 (Pentium Pro/PII/PIII) |
|
8xx |
P6/P7 (PII/PIII/P4) with hub
architecture |
|
450xx |
P6 server (Pentium
Pro/PII/PIII Xeon) |
|
E72xx |
Xeon workstation with hub
architecture |
|
E75xx |
Xeon server with hub
architecture |
|
460xx |
Itanium processor |
|
E88xx |
Itanium 2 processor with hub
architecture |
The chipset numbers listed
here are abbreviations of the actual chipset numbers stamped on the individual
chips. For example, one of the popular Pentium II/III chipsets was the Intel
440BX chipset, which consisted of two components: the 82443BX
Intel has used two distinct
chipset architectures: a North/South Bridge
architecture and a newer hub architecture. All its more recent 800 series
chipsets use the hub architecture.
AMD Athlon/Duron Chipsets
AMD took a gamble with its Athlon family of processors (Athlon,
Athlon XP, Athlon MP, and
the now-discontinued Duron). With these processors,
AMD decided for the first time to create a chip that was Intel compatible with
regards to software but not directly hardware or pin compatible. Whereas the K6
series would plug into the same Socket 7 that Intel designed for the Pentium
processor line, the AMD Athlon and Duron would not be pin compatible with the Pentium II/III
and Celeron chips. This also meant that AMD could not take advantage of the
previously existing chipsets and motherboards when the Athlon
and Duron were introduced; instead, AMD would have to
either create its own chipsets and motherboards or find other companies who
would.
The gamble seems to have paid
off. AMD bootstrapped the market by introducing its own chipset, referred to as
the AMD-750 chipset (code named Irongate). The AMD
750 chipset consists of the 751 System Controller (
Hub Architecture
The newer 800 series chips
from Intel use a hub architecture in which the former
·
It's faster. The hub
interface is a 4X (quad-clocked) 66MHz 8-bit (4x66MHzx1 byte = 266MBps)
interface, which has twice the throughput of PCI (33MHzx32 bits = 133MBps).
·
Reduced PCI loading. The
hub interface is independent of PCI and doesn't share or steal PCI bus
bandwidth for chipset or Super I/O traffic. This improves performance of all
other PCI bus connected devices because the PCI bus is not involved in these
transactions.
·
Reduced board wiring.
Although twice as fast as PCI, the hub interface is only 8 bits wide and
requires only 15 signals to be routed on the motherboard. By comparison, PCI
requires no less than 64 signals be routed on the board, causing increased
electromagnetic interference (EMI) generation, greater susceptibility to signal
degradation and noise, and increased board manufacturing costs.
This hub interface design
allows for a much greater throughput for PCI devices because there is no South Bridge
chip (also carrying traffic from the Super I/O chip) hogging the PCI bus. Due
to bypassing PCI, hub architecture also enables greater throughput for devices
directly connected to the I/O Controller Hub (formerly the
The hub interface design is
also very economical, being only 8 bits wide. Although this seems too narrow to
be useful, there is a reason for the design. By making the interface only 8
bits wide, it uses only 15 signals, compared to the 64 signals required by the
32-bit-wide PCI bus interface used by North/South Bridge chip designs. The
lower pin count means less circuit routing exists on the board, less signal
noise and jitter occur, and the chips themselves have many fewer pins, making
them smaller and more economical to produce.
Although it transfers only 8
bits at a time, the hub interface executes four transfers per cycle and cycles
at 66MHz. This gives it an effective throughput of 4x66MHzx1 byte = 266MB per
second (MBps). This is twice the bandwidth of PCI,
which is 32 bits wide but runs only one transfer per 33MHz cycles for a total
bandwidth of 133MBps. So, by virtue of a very narrow but very fast design, the
hub interface achieves high performance with less cost and more signal
integrity than with the previous North/South Bridge design.
The MCH interfaces between the
high-speed processor bus (533/400/133/100/66MHz) and the hub interface (66MHz)
and AGP bus (533/266/133/66MHz), whereas the ICH interfaces between the hub
interface (66MHz) and the ATA (IDE) ports (66/100MHz) and PCI bus (33MHz).
The ICH also includes a new
low-pin-count (LPC) bus, consisting basically of a stripped 4-bit wide version
of PCI designed primarily to support the motherboard ROM BIOS and Super I/O
chips. By using the same 4 signals for data, address, and command functions,
only nine other signals are necessary to implement the bus, for a total of only
13 signals. This dramatically reduces the number of traces connecting the ROM
BIOS chip and Super I/O chips in a system as compared to the 96 ISA bus signals
necessary for older North/South Bridge chipsets that used ISA as the interface
to those devices. The LPC bus has a maximum bandwidth of 6.67MBps, which is
close to ISA and more than enough to support devices such as ROM BIOS and Super
I/O chips.
Figure shows
a typical Intel motherboard that uses bus architecture—the
Intel D845PEBT2, which supports the Intel Pentium 4 processor. Unlike some of Intel's
less-expensive hub-based motherboards, the 845PEBT2's Intel 845 chipset doesn't
incorporate video.
Figure . Intel D845PEBT2 motherboard
showing component locations. Illustration used
by permission of Intel Corporation.
Let's examine the popular
chipsets, starting with those used in 486 motherboards and working all the way
through to the latest Pentium III/Celeron, Pentium 4, Athlon
XP, and Athlon 64 chipsets.