Billy Newsom · 01-01-1997 · Category:
What Is a Chipset?
Chipset: An integrated set of VLSI chips that perform
all of the vital functions of a computer system, including the
functions that once required separate chips. The types of devices
replaced by the chipset includes:
- memory controller
- EIDE controller
- PCI bridge
- RTC (real-time clock)
- DMA controller
- IrDA controller
- keyboard controller
- PS/2 mouse controller
- secondary cache controller
- low-power CMOS SRAM
Note that some of the above are not integrated with every chipset.
Every bit of information that is stored in memory or is sent
to any I/O device has passed through the chipset on its way to
the CPU. You can think of the CPU as a terminus or node, while
the chipset is the hub. The chipset is all about I/O and
multiplexing and data transfer. Peripherals need the chipset to
access other peripherals.
Have you ever heard of DMA? Have you ever wondered how data
bypasses the CPU on its way to the appropriate device? The DMA
controller inside the chipset does that. What keeps data pouring
in from the hard disk to the CPU from colliding with data from
other devices? The bus controllers (memory, PCI, ISA, EISA)
inside the chipset do that.
The chipset runs the show. When new chipsets emerge,
motherboard manufacturers redesign their boards to accommodate
them. Presently, more chipsets are having greater functionality,
even as costs are staying relatively constant.
The CPU can be changed. The memory can be upgraded. The hard
disk can be swapped. But the motherboard has been designed around
the capabilities of the chipset, and until you change the
motherboard, your PC will function largely the same.
Here are some examples of what properties the chipset dictates.
- Memory type: FPM, EDO, BEDO, SDRAM, parity-checking, ECC
- Secondary cache: burst, pipeline burst, synchronous, asynchronous
- CPU type: 486, P-24T, P5, P54C/P55C, Pentium Pro, Pentium II
- Maximum memory bus speed: 33, 40, 50, 60, 66, 75, 83, 100 MHz
- PCI bus synch: synchronous or asynchronous to memory bus speed
- PCI bus type: 32-bit or 64-bit
- SMP capability: single, dual, trio, or quad CPU support
- Support for features like: AGP, IrDA, USB, PS/2 mouse
- Support for built-in PCI EIDE controller and every
possible EIDE feature you can imagine: DMA mode, PIO mode, ATA/33, etc.
- Built-in PS/2 mouse, keyboard controller and BIOS, and real-time clock circuitry
As you can see, a lot of what makes a chipset nice is that it
can replace the dozens of chips that used to pock-mark a
motherboard and require detailed compatibility testing for the
motherboard designers. With a single-chip or 2-chip solution,
many chipsets can replace nearly every major controlling chip on
the motherboard. This cuts the design and testing phase of a
motherboard by perhaps 60% or more. It also, unfortunately,
increases the time it takes to bring a new chipset to market, and
reduces the options allowed. This problem is obviated with the
way Intel has built chipsets for the Pentium. (And yes, I made that
word up.) There are now (in
practice) only two chipset choices for builders of laptop and
desktop Pentium motherboards: the "Triton II," and the
430TX. The Triton I, the Triton III, and the 430MX have recently
been superseded. With only two Intel chipset options (I discount
the Triton III on purpose here), you shouldn't be surprised
that there are a lot of similarities in motherboards based on
these two designs. Intel is the leading manufacturer of chipsets
for Pentium, Pentium Pro, and Pentium II motherboards.
This description of chipsets is not meant to be a definitive
description of the underlying technologies associated with
motherboards. However, a brief description of what is hot and
what is not deserves some mention. Each definition comes complete
with a link to some more detailed information where necessary.
What Is a Chipset?
Graphics Port & practice) bus used in combination with the standard 32-bit 33MHz
PCI bus for graphics adapters to receive data from main memory
Northbridge & major bus controller circuitry, like the memory, cache, and PCI controllers.
The north bridge may have more than one discrete chip. The entire chipset is
named after the numbers on the primary or largest north bridge chip.
e.g. "FW82439HX" designates the Intel 430HX PCIset.
Southbridge & peripheral and non-essential controllers, like EIDE and serial
port controllers. The south bridge usually has only one discrete
chip, and has the benefit of being interchangeable on many different
chipsets, for example the SiS 5513 and the Intel PIIX.
BEDO Burst Enhanced Data-Out RAM & only a bit faster.
Dynamic RAM & memory bus. SDRAM is normally rated at 8, 10, or 12 ns, while
standard DRAM is rated at 60, 70, or 80 ns. In practice, SDRAM is
packaged in the relatively new 3.3 volt 168-pin unbuffered DIMM modules.
SDRAM is slowly replacing EDO and FPM.
DIMM Dual In-Line Memory Module & refers to the 168-pin 64-bit/72-bit/80-bit modules found in many
Socket 7 and Slot 1 motherboards. A 168-pin DIMM may be SDRAM,
EDO, FPM, or BEDO RAM. As far as I know, DIMM's are always 3.3 V
devices and cannot be mixed with 5 V SIMM's.
FPM Fast Page Mode & on most 386, 486, and P5 motherboards. EDO is gradually replacing
FPM. Most FPM RAM is rated at 60, 70, 80, or 100 ns, and is most
often packaged in 5 V 30-pin or 72-pin SIMM's.
Code & checking of data integrity. Memory buses may use ECC to automatically
correct single-bit errors in real-time and detect two-bit errors. Note
that a 2-bit error will usually hang the system. For main memory,
your chipset or your memory must support ECC before you gain the
benefits of it. ECC memory is very expensive and is normally
found only on high-end servers. (Some people have
tried to correct this assumption, however it is still accurate.)
Slot 1 & for the Pentium II's Single Edge Connector (SEC) module. The Pentium II
CPU and heatsink fit into the Slot 1 using rails mounted on plastic inserts.
Slot 1 to Socket 8 adapters are made to allow for Pentium Pro processors to fit
into a Slot 1.
Socket 8 & connector for the Pentium Pro CPU. The Socket 8 is a
zero-insertion force (ZIF) design that makes CPU installation quick
and easy, unlike the Slot 1 design which requires a manual and a
half-dozen pieces of plastic.
Socket 7 & originated by Intel that can be used for any P54C or P55C processor,
including the AMD K5 and K6, the Intel Pentium and Pentium MMX,
the IDT C6, and the Cyrix/IBM 6x86, 6x86L, and 6x86MX
processors. The Socket 7 is a ZIF design like the Socket 8,
and it supersedes the older Socket 5/6's that earlier P54C
(single-voltage) processors used.
Socket 4 & 5 volt Pentium. Sockets prior to the Socket 4 were less
well-defined and were used on 486-style motherboards.
Symmetric Multi-Processing & more than one microprocessor to share the load of CPU requests.
The Intel Pentium Pro natively supports four
CPU's. The Intel Pentium and Pentium II support only two
CPU's. With the aid of specialized circuitry, systems can be built with
many more than just four CPU's, although this sometimes
requires an asymmetric (front-end, back-end) system.
Multi-Processor Standard (MPS) is the specification
used by chipset makers and software developers for SMP systems.
Intel's MPS allows the owner of an Intel SMP
system to buy an off-the-shelf software product such as Linux,
Microsoft NT, SCO MPX, FreeBSD, Sun Solaris, Novell NetWare, or
IBM OS/2 by simply installing the software's
multi-processing HAL for Intel microprocessors.
Universal Serial Bus & USB is a "peripheral connection interface" for external devices.
To describe it is also to imply that it is known in the industry
as "vaporware." There just aren't many devices
that use USB for it to be a serious technology yet. Its speed is
a staggering 24 MHz (12 Mb/sec), making a run for the i-link, IEEE-1394
(Apple's FireWire) market. USB is supposed to be what you'll
connect joysticks, keyboards, modems, scanners, mice, and anything else
you use today that needs a slow SCSI or RS-232 interface.
Sure, RS-232 was the hot product of the 1980's, but hey - it still works
fine for my modem. With as slow as it is adopting USB, many
people believe that the IEEE-1394 spec will blow the doors off
USB (USB maxes out at a puny 12 Mbps compared to 400 Mbps for
i-link), leaving USB to a fate somehow reminiscent of the 80487.
Others see USB used for low-to-medium bandwidth products,
supplementing the high-end i-link products that may soon run at
speeds up to 1 Gbps.
BIOS Basic Input/Output System & software stored in ROM that is executed first during a
system's boot. The BIOS performs a power-on-self-test (POST)
which verifies vital component functions like memory, CPU, cache,
DMA, keyboard, A20 address gate, video, floppy, and hard disks.
This software may be stored on a EEPROM so that the user may
"flash" or write to the ROM. Not to be confused with
CMOS. A system's BIOS was what actually introduced me to the
idea of reverse-engineering. Now, the famous Compaq BIOS that won
court approval paved the way for Compaq to be the first
manufacturer of a 386 computer, beating IBM in their own game.
Back then, clones were declared illegal if you merely copied the
IBM BIOS and didn't pay a licensing fee. Compaq had to find
a bunch of virgin BIOS-code writers who had never seen IBM's
PC BIOS. The virgin engineers received carefully-worded
instructions from "dirty" engineers who had seen the BIOS
code. All of this was scrutinized as part of a landmark court decision
regarding cloning, reverse-engineering, and NDA's.
This revolution opened up the third-party unlicensed
BIOS-writing industry as Phoenix, AMI, and others began selling and
licensing BIOS code to clone PC builders around the world. The
story of the BIOS is what defined the IBM clone industry of the 1980's
CMOS Complementary Metal Oxide Semiconductor
& for. Although there are quite a few ways to describe CMOS (you
can always get into a TTL/CMOS logic debate or a discussion on
the properties of doped silicon), the CMOS on a motherboard is
not the generic, all-encompassing term you may be familiar with.
Rather, CMOS is merely the small 64-byte memory circuit that
holds vital configuration data used by the BIOS every time the
system is booted. The CMOS is what the Setup program writes to
whenever you update your hard disk or memory settings. The
motherboard's CMOS is sometimes in two parts & the password, the other for the setup info. Many motherboards
allow you to clear setup CMOS and/or password CMOS separately if
you wish. Since the CMOS circuit must have constant power to it
to keep its contents stored, you can clear it by moving the
jumper provided for this function. Most motherboards have a
mercury or alkaline battery to maintain the RTC and the CMOS
circuits supplied with power. Note that CMOS actually refers to
the process employed to manufacture the circuit, and it is more
properly called NVRAM (non-volatile RAM) to distinguish it from
other CMOS circuits.
ROM read-only memory & this stores the BIOS code, and is most often a 64 KB or 128 KB
Types include EPROM (erasable, programmable ROM), which
uses UV light to erase and a ROM burner to program, and EEPROM
(electrically erasable, programmable ROM), known as Flash ROM,
which can be written and erased while in-circuit.
The ROM is usually socketed with 28 pins and has a reflective sticker on
it to cover the EPROM's window. Shining UV light through this window
will erase the EPROM's memory so it can be reprogrammed.
RTC Real-Time Clock & only self-explanatory, it's the most predictable of
components on the motherboard. It receives power from a small
battery on the motherboard.
PnP Plug & that allows devices to be automatically detected and configured
by the system software, both the BIOS and the OS. Microsoft
Windows 95 is the only major OS with native PnP capabilities.
Configuration and Power Interface & API that goes beyond what APM's suspend and doze modes would
do. It was introduced by the Intel 430TX chipset as part of its
Rev. 2.1 Concurrent PCI & specification used in all current Intel chipsets, including the
430VX, 430HX, 430TX, and 440FX.
Cache-on-a-stick & found on Socket 7 motherboards. There are at least two different
versions of COAST, each related to the chipset of the
motherboard. COAST seems to be a short-lived technology with its
niche in 1996. Caches made prior to or after this time mainly use good
old-fashioned SRAM soldered to the motherboard.
& upon by Intel (for the chipsets), Microsoft (for the operating
system), and Toshiba (for the mobile PC industry) to improve
power management, increase conformity for the notebook computer,
and to specify the technologies that computer manufacturers
should comply with for maximum compatibility. This initiative
includes ACPI, Ultra DMA, Concurrent PCI, and SDRAM. See also
For other words not covered here, I will refer you to ZD's
index or the PC
- What Is a Chipset?
- A Brief History of Pentium Chipsets
- Triton: It All Started Here
- Intel Pentium Chipsets
- Non-Intel Pentium Chipsets
- Pentium Pro/II Chipsets
- The $69.00 Motherboard
- High-End Chipsets