What is speed of first generation of computer?

There really isn't exactly a "first" computer. Some of the really early ones:

• Harvard Mark I - 3 operations per second
• ABC - 30 additions/subtractions per second
• ENIAC - 5000 additions/subtractions per accumulator per second
• Zuse Z3 - roughly 1 to 3 operations per second
• Colossus - roughly 5000 enciphered characters per second