VIA/CYRIX Overclocking – how to Tweak Your PC to Unleash Its Power


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Chapter 8: VIA/CYRIX Overclocking

One Chip, Many Names

VIA Technologies, a Taiwan-based computing giant, acquired the aging Cyrix processing platform in June 1999. In the same time-frame, the company bought rights to the Centaur WinChip architecture, allowing it to enter the processor design business. While VIA is now actively developing processing platforms, it still relies on outside resources to produce its models.

Many computer users have never heard of a VIA processor. This lack of visibility can best be attributed to poor marketing, though the quality of the processors has also been in question. The original VIA Cyrix III processor never shipped to market; its architecture simply could not compete with similarly priced offerings from Intel and AMD.

In acquiring Centaur, VIA moved to redesign its failed chip. The Centaur design team had posted moderate success with WinChip; VIA was hoping to leverage that success into a viable processor design. The VIA Cyrix III, called Samuel, was derived from Centaur; it shared little technology with any earlier Cyrix design. The Samuel was underpowered, but it did establish VIA’s presence in the microprocessor market.


Figure 8-1: The VIA C3 processor

The current VIA processing platform is called C3, a name derived from Cyrix III but shortened to neutralize the stigma associated with earlier Cyrix models. The VIA C3 is essentially a fifth-generation 80586 core architecture, with extensions for compatibility with MMX and 3DNow! instruction sets. 3DNow! support is a real blessing, as the base floating-point unit of the C3 leaves much to be desired. The C3 fairs slightly better in desktop applications; it usually performs within a few percentage points of the popular Intel Celeron II for most integer-based calculations. Comparing the C3 against the AMD Duron is pointless; the entry-level Duron often outperforms even the powerful Pentium III.


Table 8-1: VIA C3 Specifications

Processor Family Model Name VIA C3

Performance Rating 733 – 933+ MHz Generation Fifth: 80586 IA-32

Operational Rates Level 1 Cache Speed 1.0x Core Rate

Level 2 Cache Speed 1.0x Core Rate Front-side Bus Speed 100 – 133 MHz

Multiplier Ratio 4.5x – 8.0+x

Physical Design Interface Packing 370 Pin Socket Core Die Size .15 micron, 52 mm2

.13 micron, 52 mm2 Transistor Count 15.8 Million

Voltage Interface Split Core and I/O Core Voltage .15 micron: 1.6 volts

.13 micron: 1.35 volts I/O Voltage 3.3 volts

Power Consumption 6.8 – 10.6 watts

Maximum Power 9.6 – 17.7 watts

Architectural Design

Core Technology In-order and Pipelined Execution


Register Support Integer = 32 bit

Floating-Point = 80 bit

Table 8-1: VIA C3 Specifications

Processor Family Model Name VIA C3

MM = 64 bit Execution Units 1x Integer

1x FPU (1/2 Speed) Data Bus Width 64 bit

Max Memory Support Physical = 4 Gigabyte

Virtual = 64 Terabyte Multi-Processor Support Not Supported

Level 1 Code Cache 64 KB 4-way Level 1 Data Cache 64 KB 4-way

Level 2 Cache 64 KB Exclusive Pre-fetch Queue 3x 16 Byte

Static Branch Prediction Supported Dynamic Branch 128 Entry


RSB Branch Prediction 16 Entry Floating-Point Processor Integrated

Multimedia Extensions MMX, 3DNow!

VIA C3 Overclocking

The VIA C3 processor’s specifications suggest great overclocking opportunities. The C3 boasts a small core die size and extremely low thermal loads, even at its highest frequency ratings. It is compatible with the widest variety of popular socket-370 motherboards, plus it offers a decent execution pipeline. Sadly, though, the C3 remains a modest overclocking option for most configurations.

The C3’s overclocking potential is highest with lower processor-speed grades. Users may find that the chip responds unfavorably to front-side bus overclocking. Most C3 chips are multiplier unlocked, however, and can scale to an additional 100 MHz.

Overclocks can peak at 950 to 1000 MHz for the best .13-micron processors. Multiplier adjustments can be performed directly within Windows using H.Oda’s popular WCPUID freeware testing application, which can be obtained at

Proper voltage can be a serious concern for the C3. Unlike competing designs from Intel, the C3 is not well suited for large increases in core voltage rates. The fastest

.13-micron models are designed for 1.35 core volts; pushing these units beyond 1.4 volts is discouraged because it seriously increases potential for core failure. Earlier

.15-micron units typically operate at .16 volts, though it is not wise to attempt more than 1.7 to 1.75 volts when overclocking them.

Expensive cooling solutions are not really necessary when overclocking the VIA C3. This chip accommodates thermal generation loads unparalleled by anything other than the mobile processor families from Intel. However, junking the passive heatsink

cooler that many companies ship with the C3 is a good idea. This cheap heatsink can barely pass for a decent socket-7 cooler, it is not a cooler for the overclocking enthusiast. Any quality socket-370 forced-air heatsink should work well for overclocking the C3.


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