The address bus in the 8085 is 16 bits wide.
The 8086/8088 has an internal 20-bit address bus and 16-bit data bus. Externally, the address bus is 20-bits, and the data bus is 16-bits for the 8086 and 8-bits for the 8088.The data bus in the 8086 is 16 bits in size, while the address bus is 20.
You need 20 bits of address bus to address 1 Mb of memory.
MCA
8 bits
The external data bus can be as wide as desired, given the necessary compromises between performance, complexity, and cost. The wider the bus, the faster the theoretical aggregate data transfer rate. In the 8085 and 8088, the external data bus is 8 bits wide; in the 8086, it is 16 bits wide; in the 80386, it is 32 bits wide; and in the modern incarnations of 64 bit processors, it is 64 bits wide.
For the Pentium the front side data bus is 64 bits wide. The back side is 32 bits wide.
Width
The original XT PC computers internal data bus was 8 bits wide and was called the ISA bus or Industry Standard Architecture An improvement to this design was the internal data bus that was 16 bits wide and named EISA or Extended Industry Standard Architecture EISA was the cutting edge design when the Intel 386 processor was introduced.
32 bits wide
The data bus in the 8086 is 16 bits in size, while the address bus is 20 (16bits would only address 64KB of memory, an extra 4 bits allows to address the total of 1MB, this is done trough segmentation of the memory). To form a multiplexed of data bus and address bus, four bits of 8086 address bus are grounded.
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