PWA-IH4077D © 1992 Mitac
The PWA-IH4077D is a high-performance 80486 Baby AT motherboard engineered and manufactured by the major Taiwanese OEM system vendor MiTAC around 1992 to 1993. Built to deliver an optimized local bus platform for mid-range desktop clones and workstations, the mainboard relies on the highly stable UMC UM8401 (Northbridge) and UM8402 (Southbridge) core logic chipset. It centers around a flexible 168-pin Socket 1/2 footprint that natively accommodates Intel 80486SX, DX, and clock-doubled DX2 microprocessors running at synchronous Front-Side Bus (FSB) speeds of 25 MHz or 33 MHz. Its physical expansion capabilities are driven by three high-speed 32-bit VESA Local Bus (VLB) slots integrated at the base of six rugged 16-bit ISA slots. Memory routing configurations are split into two distinct generation topologies, offering four 30-pin SIMM sockets alongside two high-density 72-pin SIMM sockets supporting Fast Page Mode (FPM) DRAM, complemented by a modular DIP-packaged secondary L2 write-back static cache (SRAM) matrix expandable up to 256 KB.
The OEM Mass Production Specialist: While names like AMI or Supermicro targeted high-end boutique servers, MiTAC was a massive hardware powerhouse focused on high-volume, enterprise-grade reliable manufacturing. The PWA-IH4077D layout was optimized to eliminate unneeded auxiliary logic, allowing third-party international system builders to bundle ultra-fast 32-bit VLB graphics and caching controllers at a highly competitive retail price point.
The Mixed SIMM Transitional Layout: This motherboard revision represents a fascinating technological bridge in early 1993 computing layout trends. By mounting both old 30-pin SIMM sockets and the newer, wider 72-pin SIMM sockets on the same PCB, MiTAC saved money for upgrading users, allowing corporate IT departments to reuse legacy memory modules from discarded 386 systems alongside newer, higher-capacity RAM sticks.