**1. Serial Adder:**

A serial adder is used to add two binary numbers in serial form. The two binary numbers to be added serially are stored in two shift registers. The circuit adds one pair at a time with the help of one full adder. The carry output from the full adder is applied to a D flip-flop, the output of which is then used as a carry input for the next pair of significant bits. However the sum bit S from the output of the full adder can be transferred into a third shift register.

**2. Parallel Adder:**

A parallel adder is a combinational digital circuit that adds two binary numbers in parallel form. It consists of full adders connected in cascade, with the output carry from each full adder connected to the input carry of the next full adder.

**Difference between Serial Adder and Parallel Adder:**

Serial Adder | Parallel Adder |
---|---|

It is used to add two binary numbers in serial form. | It is used to add two binary numbers in parallel form. |

A serial adder uses shift registers. | A parallel adder uses registers with parallel loads. |

It requires single full adder. | It requires multiple full adders. |

Carry flip-flop is used in serial adder. | Ripple carry adder is used in parallel adder. |

Serial adder is a sequential circuit. | Parallel adder is a combinational circuit. |

In serial adder, propagation delay is less. | In parallel adder, propagation delay is present from input carry to output carry. |

Number of required full adder is fixed i.e. one. | Number of required full adder is equal to the number of bits in the binary number. |

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