As Framework detailed, the mainboard is a standard Mini-ITX form factor with ATX headers, a PCIe x4 slot, and a typical set of rear I/O (2x USB4, 2x DisplayPort, HDMI, and 5Gbit Ethernet), meaning ...
[Mike] from Leaded Solder has a soft spot for old computers ... The MSX has two cartridge slots, an ‘internal’ slot for the BIOS and RAM and a fourth for ‘misc’ use.