Micro Expander

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Micro Expander Model 1, also known as the Expander (sold in Europe as the PAL), was an S-100-based microcomputer released in May 1981. It was designed by Lee Felsenstein, the creator of the Sol-20 home computer. The machine combined a built-in full-size keyboard, four S-100 expansion slots, and a Z80A CPU running at 3.58 MHz. It started with 64 KB of RAM, expandable to 512 KB, and could display video in monochrome or color across several modes.

The Expander could run CP/M, MP/M, or other Z80 software. It shipped with Microsoft BASIC on disk, a cassette BASIC interpreter, and a 4 KB ROM monitor. It included a real-time clock, a small sound system, and cassette and RS-232 interfaces. Video options included monochrome text (80×24), monochrome graphics (160×72), color text (40×24), and color graphics (80×72) with up to 256 colors.

The device used the S-100 bus, with four expansion slots (one already filled by RAM). Cards could be piggybacked to add more. In Europe it was marketed as the PAL. A 16-bit upgrade board appeared in 1982, and the Expander stayed listed into 1983, but only about 200 units were produced. Micro-Expander, Inc. faced financial difficulties and shut down in January 1987. The project began after Processor Technology’s Sol-20 line ended; Swedish investor Mats Ingemanson helped market and fund manufacturing through Manu-Tronics in Wisconsin.