An Arduino Uno runs at 16MHz, and averages about 1.5 instructions per clock (estimated by multiplying the best case 1 instruction per clock by 1.5), so about 11M instructions per second.
The FACOM128B is asynchronous, and takes about 0.15s per instruction using the same estimation (1.5x best case), so about 7 instructions per second. See timings at: http://museum.ipsj.or.jp/en/computer/dawn/0012.html
However, the FACOM128B is 69bit, and the Atmega is only 8bit (it can do some 16bit operations, but those are limited to certain registers and operations, so I'll just assume it's only 8bit). 69 is about 9 times bigger than 8, so I'll assume the FACOM128B can do about 9 times as much work per operation (there is overhead in calculating wider results from narrow operations, but the full width isn't always needed, so this simple estimate seems reasonable to me).
Therefore the FACOM128B is like an Arduino with about a 190000x slower clock.
The FACOM128B is asynchronous, and takes about 0.15s per instruction using the same estimation (1.5x best case), so about 7 instructions per second. See timings at: http://museum.ipsj.or.jp/en/computer/dawn/0012.html
However, the FACOM128B is 69bit, and the Atmega is only 8bit (it can do some 16bit operations, but those are limited to certain registers and operations, so I'll just assume it's only 8bit). 69 is about 9 times bigger than 8, so I'll assume the FACOM128B can do about 9 times as much work per operation (there is overhead in calculating wider results from narrow operations, but the full width isn't always needed, so this simple estimate seems reasonable to me).
Therefore the FACOM128B is like an Arduino with about a 190000x slower clock.