PM 904F CPU Module. This CPU module is the high-end base unit of the Freelance AC 900F controller family and has and 8 MB battery buffered SRAM. It is good enough for around 1.500 IOs, depending on the application. 4 Ethernet interfaces, 800 MHz CPU clock, 48 MB Controller Memory: 16 MB battery buffered SRAM, 32 MB DRAM. 4 slots for assembling Communication Interface Module.