Epson 723-MA PII-M1 Motherboard Intel 386SX i387SX 20MHz Y72320100101 9103G

Epson 723-MA PII-M1 Motherboard Intel 386SX i387SX 20MHz Y72320100101 9103G

The Epson 723-MA is a proprietary system board designed and manufactured by Epson Portland, Inc. for use in Epson's 386SX-based personal computers. It carries the board revision designation PII-M1 and PCB assembly number Y72320100101, with a date code of 9103G placing manufacture in early 1991. The board is built around an Intel 80386SX processor and includes an Intel i387SX math coprocessor (N80387SX-20, 20 MHz) for floating-point acceleration — a separate coprocessor chip that was optional on many 386SX systems but is present here.

Specifications & What's Included

• Manufacturer: Epson Portland, Inc.
• Board Model: 723-MA
• Board Revision: PII-M1
• PCB Assembly Number: Y72320100101
• Date Code: 9103G (Week 3, 1991)
• CPU: Intel 80386SX
• Math Coprocessor: Intel i387SX 20 MHz (N80387SX-20, SZ369) — installed
• Memory: 30-pin SIMM slots — multiple banks visible (at least 7 slots across two areas)
• Bus: ISA expansion slots along right edge
• Storage Interface: 40-pin IDE/floppy-style header connector
• I/O: PS/2 keyboard port, 2× DB9 serial ports, 1× DB25 parallel port — all integrated on-board
• Form Factor: Proprietary (Epson system-specific)
• Certifications: UL listed (mark visible on board)
• Included: Board only — no RAM modules, cables, or accessories

Applications

The Intel 386SX was Intel's mainstream 32-bit processor of the late 1980s and early 1990s, offering a 32-bit internal architecture with a 16-bit external data bus that reduced system cost compared to the full 386DX. Epson was a significant player in the IBM-compatible PC market of that era, producing complete desktop and tower systems under its own brand. The 723-MA PII-M1 is a proprietary board built for a specific Epson system rather than a generic AT-form-factor design, which means it is primarily of interest to collectors maintaining or restoring Epson 386SX machines, or to researchers and enthusiasts working with early-1990s Epson PC hardware. The i387SX math coprocessor installed on this board was used to accelerate floating-point-intensive applications such as CAD, spreadsheets, and scientific software — programs that ran noticeably faster with a coprocessor present. This board dates firmly to the early ISA/DOS computing era, prior to the widespread adoption of PCI bus and Windows 3.1.