Hi Kevin, output after boot: R0 R4 SP PC(at time of boot initiated) $ boot device codes, suffix n for unit number n, n=0,1,..., empty=0 TT terminal paper tape DK RK11 moving head cartridge DT DECtape MT TM11 magtape (7 or 9 track, 800 BPI, odd parity, dump mode) DP RP11 moving head disk pack CT TA11 cassettes PR PC11 high-speed paper tape reader DX RX11 diskette some M9301 versions additionally support MASSBUS devices. DX<cr> should work fine for you. The DX boot appears to be at address 173546. I will fax the program code at that address. Do you have the RX11 controller register descriptions ? John