INTRODUCTION TO CHIPSETS
Socket Type
The socket type used to mount the CPU on the motherboard is the most common grouping for chipsets. You will find Socket 7 chipsets in one group, Socket 8 chipsets in another, Socket 1 and 370 chipsets in a third, and Slot Achipsets in another. There are chipsets that do not conform to this grouping technique, such as AMD’s K7 chipset and others that generally form their own separate groupings.
North Bridge and South Bridge
Another
characteristic that sets one chipset apart from another is whether it has one,
two, or more chips in the set. The two-chip chipset, which contains what is
called the north bridge and the south bridge, is the most common, but some
manufacturers, such as SiS and VIA, produce mostly single chipsets today. Other
chipsets have as many as six chips in the set. The north bridge is the major
bus circuitry that provides support and control for the main memory, cache
memory, and the PCI bus controllers. The north bridge is typically a single
chip (usually the larger of a two or more chipset), but it can be more than one
chip. In a chipset, the north bridge supplies the chipset its alpha designation
and distinction in a chipset family. For
example, the chip FW82439HX is the north bridge chipof the Intel 430HX
chipset. The south bridge includes the controllers for the peripheral
devices and any controllers not essential to the PC’s basic functions, such as
the EIDE (Enhanced Integrated Device Electronics) controller and the serial
port controllers. The south bridge is typically only one chipand is common
among all variations in a chipset family and even between manufacturers, such
as the SiS 5513 and the Intel PIIX south bridge chips.
Processor
Generations
Another
grouping technique that is fading away is the chipset’s, and processor’s,
generation. As processors have evolved from the early days, processors have
been grouped by their evolutionary generation. For example, the 8088 was a first-generation
processor, the 386 a third-generation processor, the 486 a fourth-generation
processor, the Pentium a fifth-generation processor, and so on. When Intel was
the dominant processor manufacturer, the generations were much easier to
follow, but now that AMD and VIA Cyrix processors have gained a foothold in the
market, the generation of processors is more fuzzy. Chipsets emerged on the
processor’s fourth generation, and you will see some legacy chipsets
categorized to the generation of the processor it supports.
CONTROLLER CHIPS
Generally, a chipset does not
incorporate all of the controllers used to direct the actions of every
peripheral device on the PC. In addition to the chipset, there are at least
two, and possibly more, controllers mounted directly on the motherboard. In
most cases, the motherboard will have at minimum a keyboard controller and an
I/O controller (a.k.a. the Super I/O controller). Some expansion cards, such as
video adapters, sound cards, network interface cards (NICs), and SCSI (Small
Computer System Interface) adapters, have built-in controller chips. Individual
controller chips come in all sizes and shapes, as illustrated in Figure.
A controller chip controls the
transfer of data to and from a peripheral device, such as a disk drive, the
monitor, the keyboard, or a printer. All of these devices depend on a device controller
to interact with the CPU and the rest of the PC. For the most part, PC users don’t
ever think about controller chips on their systems. In fact, most users
probably don’t even know they exist.Howdata gets to and from the keyboard is
not of concern, only that it does.
On a PC, a controller is
typically a single chip that either mounts directly on the motherboard or on a
card that is inserted in an expansion slot on the motherboard. Because they
control the flow of data to and from peripheral devices, controllers must be
matched to the bus architecture of the PC.
Bus Architectures
The
bus architecture of the PC is made upof the wires, connectors, and devices that
move data and instructions around the PC
(see Chapter 11 for more information on expansion bus architectures). The bus
structure, which got its name from the fact that it resembles the lines on a
city bus map, connects the controllers on the motherboard, the CPU, memory, I/O
ports, and expansion slots. The PC’s bus architecture becomes very important
when you add additional device controller cards to the motherboard’s expansion
slots. Most of the latest motherboard designs include expansion slots for
multiple bus structures, including PCI (Peripheral Component Interconnect) and
AT Bus, and possibly SCSI. Each of the bus architectures supported on a
motherboard requires a bus controller chip. While not technically a bus
architecture, another interface type you will see listed as a major feature of
some, especially the newer chipsets, is support for AGP (Accelerated Graphics
Port).AGPis a 66MHz bus that is usually combined with a 32-bit 33MHz PCI
bus to provide advanced support and faster data transfers from main memory for
video and graphics adapters.
AT Bus
The
AT expansion bus is included on current PC motherboards primarily for
backward compatibility to expansion
cards from older systems, such as network adapters. The AT bus, which runs at
8MHz and uses a 16-bit data path, is commonly referred to as ISA (Industry Standard Architecture). However, the ISA bus standard
also includes the 8-bit PC XT bus, which is rarely used on any current PC. Another
bus related to the AT bus is the Extended
Industry Standard Architecture, or EISA, bus. EISA bus expansion slots
have been included on some motherboards since the time of the 386 processor. It
is a 32-bit bus but is also backward compatible to the AT and ISA buses.
Local Bus
AT
and ISA bus structures are unable to keepupwith the speeds required for
high-resolution graphics and faster processors, so many manufacturers have
moved to what are called local bus
architectures.Alocal bus architecture is more directly connected to
the microprocessor than nonlocal buses by communicating directly to the
processor through its dedicated controller and bypassing the standard bus controller.
Although they provide for faster data movement, local buses do not support many
devices, which is why most motherboards
also include AT or ISA expansion slots as well. The most common of the local
bus architectures are the PCI and the VESA (Video Electronics Standards
Association) local bus, or VL-bus. Of these two, the PCI, promoted by Intel, is becoming the de facto standard
for virtually all Pentium class computers.
SCSI Bus
The
Small Computer System Interface, or SCSI (pronounced “skuzzy”) is a bus
architecture that attaches peripheral devices to a PC through a dedicated
controller card. SCSI supports very fast data transfer and multiple devices over
the same I/O bus structure. Very few PCs, outside of the Macintosh, feature a
SCSI interface as a standard, and if this bus is desired, it must be added to
the PC through an expansion slot, typically a PCI slot.
Keyboard
Controller
The
keyboard controller’s name describes what it does—it controls the keyboard.
More specifically though, it controls the transfer of data from the keyboard to
the PC. The keyboard controller on the motherboard interacts with a controller
located inside the keyboard over a serial link built into the connecting cable
and connector. When the keyboard controller receives data from the keyboard, it
checks the data’s parity, translates the scan code, places the data in its
output buffer, and notifies the processor that the data is in its buffer. The
keyboard controller is quite common on
most older PCs, but newer PCs either include this control function in the chipset
or in the Super I/O chip.
The functions performed by the keyboard controller, or its equivalent, are as follows:
1. Keyboard control and translation When a key is pressed on the keyboard, a scan code is sent from the controller inside the keyboard to PC’s keyboard controller, which then signals the processor through IRQ1 (interrupt request 1). The keyboard controller then translates the scan code into the character it represents and places it on the bus to move it to the appropriate location in memory.
2. Support for the PS/2 mouse On those systems that have an integrated PS/2 connector on the motherboard, the keyboard controller supports its functions. This port is most commonly used to connect a PS/2-style mouse.
3. Access to the HMA Although the support for the High Memory Area of system memory (RAM) is now incorporated into the system chipset on most newer PCs, access to this part of memory is controlled through the keyboard controller. See Chapter 7 for more information on the High Memory Area.
Super I/O Controller
The Super I/O (input/output)
controller chip includes many controller functions that were previously
performed by many separate chips. Combining these functions provides an economy
of scale for similar activities and minimizes the space required on the
motherboard and the cost of the chips used to support these activities. The “super”
in its name refers to the fact that the Super I/O controller combines many other chips and not what or how it carries
out its functions. This chip controls the standard input/output peripheral
devices and ports found on virtually every system. These functions can be
combined onto a single chipbecause they control mature standardized devices
that are virtually the same on every PC. Combining them on a single I/O chip frees
the motherboard and system chipset to control other high-priority functions.
On some older PCs, many of the
functions of the Super I/O controller were provided through I/O controller
expansion cards, such as control for serial and parallel ports and the hard
disk drive. Because these functions are common to every PC, incorporating them into
a single chip placed on the motherboard has also freed up an expansion slot.
The major functions of the Super I/O controller chip are as follows:
1. Serial ports The UART (universal asynchronous receiver-transmitter) is used to drive the serial ports and the control functions of data transfer are included in the Super I/O chip.
2. Parallel ports The functions that drive the parallel ports, including the various parallel port standards, EPP (Enhanced Parallel Port) and ECP (Enhanced Capabilities Port), are included in the Super I/O controller.
3. Floppy disk drives Support for the floppy disk drive and floppy-disk type tape drives are included on the Super I/O chip.
4. Miscellaneous functions Newer versions of the Super I/O controller may also incorporate the keyboard controller’s functions, the real-time clock, and perhaps the IDE hard disk controller, although this is more commonly found in the system chipset.
CHIPSETS
One of the fundamental design
facts of a PC is that its microprocessor is always faster than the peripheral
devices to which it must communicate. This fact has forced designers to
develop interfaces that serve as buffers between the slower devices and the
faster CPU to match up their speeds and help with the timing of the operations.
The very first PCs had an individual chip to control each of the various operations.
It was common for an early PC to have the following separate chips:
1. Math coprocessor interface This chip controls the flow of data between the processor and math coprocessor.
2. Clock generator This chip controls the timing of the PC’s operations.
3. Bus controller chip This chip controls the flow of data on the motherboard’s buses.
4. DMA controller This chip controls the processes that allowed peripheral devices to interact with memory without involving the processor.
5. Programmable peripheral interface (PPI) This chip supervises some of the simpler peripheral devices.
6. Floppy disk controller (FDC) This chip controls the PC’s diskette and tape drives.
7. CRT controller This chip facilitates the PC’s display.
8. UART (universal asynchronous receiver transmitter) This chip is used to send and receive synchronous serial data.
Chipset
Characteristics
The characteristics of a chipset
can be broken down into six categories: host, memory, interfaces, arbitration,
south bridge support, and power management. Each of these categories defines
and differentiates one chipset from another.
The characteristics defined in each of these categories are as follows:
1. Host This category defines the host processor to which the chipset is matched along with its bus voltage, usually GTL+ (Gunning Transceiver Logic Plus) or AGTL+ (Advanced Gunning Transceiver Logic Plus), and the number of processors the chipset will support.
2. Memory This category defines the characteristics of the DRAM support included in the chipset, including the DRAM refresh technique supported, the amount of memory support (in megabits usually), the type of memory supported, and whether memory interleave, ECC (error-correcting code), or parity is supported.
3. Interfaces This category defines the type of PCI interface implemented and whether the chipset is AGP-compliant, supports integrated graphics, PIPE (pipelining), or SBA (side band addressing).
4. Arbitration This category defines the method used by the chipset to arbitrate between different bus speeds and interfaces. The two most common arbitration methods are MTT (Multi- Transaction Timer) and DIA (Dynamic Intelligent Arbiter).
5. South bridge support All Intel chipsets and most of the chipsets for all other manufacturers are two processor sets. In these sets, the north bridge is the main chip and handles CPU and memory interfaces among other tasks, while the south bridge (or the second chip) handles such things as the USB and IDE interfaces, the RTC (real-time clock), and support for serial and parallel ports.
6. Power management All Intel chipsets support both the SMM (System Management Mode) and ACPI (Advanced Configuration and Power Interface) power management standards.
Chipset Built-in Controllers
The controllers and devices included in a chipset are typically those that are common to virtually every PC of the type the chipset is designed to support.
The controllers and devices usually included in a chipset are as follows:
1. Memory controller This is the logic circuit that controls the reading and writing of data to and from system memory (RAM). Other devices on the PC wishing to access memory must interface with the memory controller. This feature also usually includes error handling to provide for parity checking and ECC (error-correcting code) for every memory word.
2. EIDE controller Nearly all mid- to upper-range motherboards now include at least one EIDE connector for hard disks, floppy disks, CD-ROMs, DVDs, or other types of internal storage drives. The EIDE controller typically supports devices with ISA, ATA, and perhaps an ATA-33 or Ultra-DMA (UDMA) interface.
4. PCI bridge Like a network bridge that connects two dissimilar networks, this device logically connects the PCI expansion bus on the motherboard to the processor and other non-PCI devices.
5. Real-time clock (RTC) This clock holds the date and time on your PC; this is the date and time that is displayed to you on the monitor and is used to date-stamp file activities. This should not be confused with the system clock that provides the timing signal for the processor and other devices.
6. DMA (Direct Memory Access) controllers The DMA controller manages the seven DMA channels available for use by ISA/ATA devices on most PCs. DMA channels are used by certain devices, such as floppy disk drives, sound cards, SCSI adapters, and some network adapters, to move data into memory without the assistance of the CPU.
7. IrDA controller IrDA (Infrared Data Association) is the international organization that has created the standards for short-range, line-of-sight, point-to-point infrared devices, such as a keyboard, mouse, and network adapters. The IrDA port on your system is that small red window on the front or side of notebook and some desktop computers.
8. Keyboard controller A chipset may include the keyboard controller, and many of the newer ones do. The keyboard controller is the interface between the keyboard and the processor. See the previous section for more informatio on this device.
9. PS/2 mouse controller When IBM introduced the PS/2 system, the controller for the mouse was included in the keyboard controller. This design has persisted and usually wherever the keyboard controller is, so is the PS/2 mouse controller. This device provides the interface between the PS/2 mouse and the processor.
10. Secondary (Level 2, or L2) cache controller Secondary (L2)
cache is located on the motherboard, a daughter board, or as on the Pentium Pro,
in the processor package, and caches the primary memory (RAM), the hard disk,
and the CD-ROM drives. The secondary cache controller controls the movement of
data to and from the L2 cache and the processor.
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