Question

Explain the implications of data bus which is multiplexed with address bus!

Answer 1

Generally ,not all processors used to multiplex their address and data buses. Most of processors that possess this feature of multiplexed data bus and address bus are older processors from the 70s and 80s, like the 8086, which multiplexed the data bus with the primary 16 bits of the address bus.

The primary advantage is fairly straightforward : you would like less pins on your processor, making it smaller and cheaper.

However, there's an outsized disadvantage therein each access now takes an additional cycle, and can't be overlapped. This impacts processor bandwidth.

This working model for processors was fine with these early CISC chips, when every instruction took multiple cycles to execute and the chip itself wasn't pipelined. But with modern architectures with single cycle instructions, deep pipelining, and multiple load/stores per clock, this is not doable anymore.