Forethought Systems produced a motherboard, the KIMSI, for the KIM-1 in 1977 that enables to add 8 S-100 boards to a KIM-1.
The S-100 standard, developed for the IMSAI and such 8080/Z80 systems, was a huge success that made affordable standardized systems available, mostly with CP/M as operating system.
The KIMSI married the 6502 world to these pool of boards. The KIMSI was sold as kit, with one S-100 connector. OF the KIMSI’s I have seen most were used with a memory board.

I acquired a KIMSI in August 2026. It was build into a plexiglas/aluminium case, with a KIM1 (Rev G) and a ‘microcalculator board’. For photos see below.

	KIMSI Interface/Motherboard Assembly /Operating manual Improved version August 2026
	KIMSI brochure

The BETSI: S-100 bus for the PET

My KIMSI

I acquired a KIMSI in August 2026. It was build into a plexiglas/aluminium case, with a KIM1 (Rev G) and a ‘microcalculator board’. I took the system apart, no room to store the big ugly thing.

Other KIMSI photos from the internet