30H (SiS 85C496/85C497 chipset) - MAME machine

Motherboard published 32 years ago:

30H © 1994 Soyo

Released by SOYO Computer in late 1994, the 30H is a high-performance Baby AT motherboard that bridges the gap between fourth-generation (486) processing power and fifth-generation (Pentium) peripheral standards. While earlier 486 boards relied on the long, electrically volatile VESA Local Bus (VLB), the SOYO 30H implemented a native PCI (Peripheral Component Interconnect) bus architecture, making it a premium choice for power users transitioning into the Windows 95 era.

The board centers around a standard Socket 3 configuration, featuring highly versatile voltage regulation capabilities (supporting both 5V and power-saving 3.3V configurations). This allows it to natively drive everything from older Intel 486DX-33 chips to high-speed clock-tripled Intel 486DX4-100 processors, as well as the enthusiast-favorite AMD Am486DX4-100 and late-model Am5x86-133 chips. The memory layout completely drops the restrictive 30-pin SIMM format, offering four high-density 72-pin SIMM slots across two banks. Its external Level 2 cache layer utilizes standard DIP-packaged SRAM chips, easily expandable up to 256KB or 512KB.

The 30H features a hybrid expansion array consisting of 4 industry-standard 16-bit ISA slots paired with 3 white 32-bit PCI slots. The logic engine driving the entire board is typically powered by a highly reliable, late-generation 486 PCI chipset—most notably the SiS 85C496 / 85C497 or an optimal UMC equivalent—which provides robust PCI-to-ISA bridging and built-in IDE data transfer optimizations.

TRIVIA
The SiS 496/497 Golden Combo: The choice of chipset on the 30H was a major selling point. The Silicon Integrated Systems (SiS) 85C496/497 chipset is legendary among retro-hardware builders for being one of the fastest and most trouble-free 486 PCI architectures ever manufactured. Unlike early Intel Saturn (420TX) chipsets, which suffered from severe bugs and lacked modern features, the SiS chipsets on the SOYO 30H provided full PCI 2.0 compliance, giving users perfect compatibility with early PCI graphics cards like the S3 Trio64 or Matrox Millennium.

The 30H Secret Type Code: During the 1990s, SOYO rarely splashed long model numbers on the surface silkscreen of their motherboards. Instead, they relied on a shorthand internal cataloging code. In official tech support documentation from the era, older boards were group-sorted by these signatures; the "25J/K/L" line handled standard VLB setups, while the "30H" marker was exclusively reserved for their top-of-the-line PCI 486 variants.

The 31,000-Note System Parallel: Just like the 486 processing world it inhabited, the 30H motherboard relies heavily on precise system timings. Because the PCI bus on this board runs asynchronously or synchronously with the CPU's Front Side Bus (FSB), pushing the motherboard beyond its standard 33MHz limit to "overclock" an AMD chip to a 40MHz or 50MHz bus speed will instantly alter the PCI divider, frequently causing early PCI controllers or sound cards to drop data packets.

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