Simplify the following text for a Grade 13 native English-speaking person.
Original: Historically , 4-bit microprocessors were replaced with 8-bit , then 16-bit , then 32-bit microprocessors , then 64-bit microprocessors .
Simplified: Historically , 4-bit microprocessors were replaced with 8-bit , then 16-bit , then 32-bit microprocessors .