Tomato board 4DPS © 1995 ZIDA
The Tomato Board 4DPS is one of the most famous and widely distributed late-generation 80486 Baby AT motherboards, manufactured by Zida Technologies starting around 1995. Built around a flexible 168-pin Socket 3 architecture, it is driven by the highly acclaimed SiS 85C496 (Northbridge) and SiS 85C497 (Southbridge) "Green PCI" core logic chipset. The board accommodates an exhaustive matrix of 486-class processors, including Intel 486SX/DX/DX2/DX4, AMD Am486, and Cyrix chips, with full support for late-era 3.3V and write-back cache microprocessors like the AMD Am5x86-133. Its expansion layout includes three 32-bit PCI slots and four 16-bit ISA slots, alongside natively integrated PCI Multi-I/O controllers managing dual Enhanced IDE (PIO Mode 4), Floppy, and high-speed Serial/Parallel interfaces. Memory handling consists of four 72-pin SIMM sockets supporting up to 64 MB of RAM, complemented by a modular DIP static RAM (SRAM) L2 cache subsystem expandable up to 512 KB.
The "Fake Cache" Controversy: The Tomato 4DPS is notorious in retro-computing history for being at the center of the 1990s "fake cache" scandal. To achieve impossibly low retail prices, some batches of this board shipped from factories with non-functional plastic DIP pieces stamped "Write-Back Cache" or SRAM soldered directly into the cache sockets, or with real chips that weren't actually wired to the chipset traces. Users had to verify via diagnostic software if their L2 cache was authentic.
The Tiny PCI Champion: Despite its budget nature, the SiS 496/497 chipset implementation on the 4DPS made it an absolute workhorse. It bypassed the timing instabilities and short distance restrictions of the older VESA Local Bus (VLB), allowing users to safely pair late-486 CPUs with modern, inexpensive PCI components like the 3dfx Voodoo, S3 Trio64, or Realtek network cards.