What this base unit packs
Mitsubishi FX3U-128MT/ES-A combines CPU, power supply, 64 inputs, and 64 transistor outputs in a 350 mm wide chassis. Built-in high-speed counters and positioning outputs mean many motion control applications don't need a separate module. The transistor source outputs sink loads directly at switching speeds a relay type can't match.
350 mm wide unit — check your DIN-rail or backplane span. Depth is 86 mm; shallow enclosures work. Inputs accept 24 VDC sink or source; outputs are transistor source. The 64 inputs and 64 outputs are arranged in banks; verify the terminal layout in the hardware manual before laying out cable ducts. High-speed counter inputs share some input points — plan accordingly if you use them.
Common sourcing questions
Will this drop into a panel wired for an FX5U-80MT/ESS? No — different width, different I/O count (40 vs 64 per side), and different terminal assignments. You'd need a new layout and possibly a program port.