Why NAND Based Design is better than NOR Based Design

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i) PMOS in NAND is in parallel while that in NOR is in series

ii) Parallel PMOS makes a stronger pull up network than serial PMOS

iii) Since hole mobility is lesser than electron mobility, NAND-based design is faster than that of NOR-based design (because of parallel PMOS)

iv) t_phl and t_plh (high to low, low to high times) are more symmetric in NAND than in NOR. t_plh of NOR is slower because of the series PMOS.