Chipset

In computing, the term "chipset" is commonly used to refer to a set of specialized chips on a computer's motherboard (or "main board"), and even expansion cards.

North and South Bridges of a Mainboard

Based on Intel Pentium-class microprocessors, the term chipset often refers to a specific pair of chips on the motherboard: the northbridge and the southbridge.

The northbridge links the CPU (Central Processing Unit) to very high-speed devices, especially main memory and graphics controllers, and the southbridge connects to lower-speed peripheral buses (such as PCI or ISA). In many modern chipsets, the southbridge typically contains some on-chip integrated peripherals, such as Ethernet, USB, and audio devices.

A chipset is usually designed to work with a specific family of microprocessors. Because it controls communications between the processor and external devices, the chipset plays a crucial role in determining system performance.

Chipset Manufacturing

The manufacturer of a chipset often is often independent from the manufacturer of the motherboard.

Current manufacturers of chipsets for PC-compatible motherboards include NVIDIA, AMD, VIA Technologies, SiS, Intel and Broadcom. Apple computers and Unix workstations from Sun, NeXT, SGI, and others have traditionally used custom-designed chipsets.

VLSI (Very Large Scale Integration) of Chipsets

VLSI is the process of creating integrated circuits by combining thousands of transistors into a single chip.

VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor, or CPU, is a VLSI device. The term is no longer as common as it once was, as chips have increased in complexity into billions of transistors.

VLSI Challenges

As microprocessors become more complex due to technology scaling, microprocessor designers have encountered several challenges which force them to think beyond the design plane, and look ahead to post-silicon:

Power Usage and Heat Dissipation

As threshold voltages have ceased to scale with advancing process technology, dynamic power dissipation has not scaled proportionally. Maintaining logic complexity when scaling the design down only means that the power dissipation per area will go up. This has given rise to techniques such as dynamic voltage and frequency scaling (DVFS) to minimize overall power.

Process Variation

As photolithography techniques tend closer to the fundamental laws of optics, achieving high accuracy in doping concentrations and etched wires is becoming more difficult and prone to errors due to variation. Designers now must simulate across multiple fabrication process corners before a chip is certified and ready for production.

Stricter Design Rules

Due to lithography and etch issues with scaling, design rules for layout have become increasingly stringent. Designers must keep ever more of these rules in mind while laying out custom circuits. The overhead for custom design is now reaching a tipping point, with many design houses opting to switch to electronic design automation (EDA) tools to automate their design process.

Timing and Design Design Closure

As clock frequencies tend to scale up, designers are finding it more difficult to distribute and maintain low clock skew between these high frequency clocks across the entire chip. This has led to a rising interest in multi-core and multiprocessor architectures, since an overall speedup can be obtained by lowering the clock frequency and distributing processing.

First-pass Success

As chip die sizes shrink (due to scaling), and wafer sizes go up (to lower manufacturing costs), the number of dies per wafer increases, and the complexity of making suitable photomasks goes up rapidly. A mask set for a modern technology can cost several million dollars. This non-recurring expense deters the old iterative philosophy involving several "spin-cycles" to find errors in silicon, and encourages first-pass silicon success.

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