The question asks about the size of the address bus in an 8086 microprocessor. Understanding the address bus is crucial for comprehending how a microprocessor interacts with memory.

8086 Address Bus Fundamentals

An address bus is a collection of electrical lines used by the central processing unit (CPU) to specify a physical address in memory or an input/output (I/O) device. The number of bits in the address bus determines the total amount of memory a microprocessor can directly access. Each unique address corresponds to a specific memory location.

8086 Address Bus Specification

The 8086 microprocessor is well-known for its specific architecture. It features a 20-bit address bus. This means that the 8086 has 20 separate lines dedicated to carrying address information. Each of these 20 lines can be either a 0 or a 1, allowing for a vast number of unique address combinations.

With a 20-bit address bus, the 8086 can generate $2^{20}$ unique memory addresses. To calculate the total memory capacity this allows, we perform the following calculation:

• The number of unique addresses is $2^{20}$.
• We know that $2^{10}$ is approximately 1 kilobyte (KB) or 1024 bytes.
• Therefore, $2^{20}$ bytes can be expressed as $2^{10} \times 2^{10}$ bytes, which is $1 \text{ KB} \times 1 \text{ KB}$.
• This results in $1 \text{ MB}$ (Megabyte) of addressable memory.

So, the 20-bit address bus of the 8086 allows it to directly address 1 Megabyte of physical memory space, from address 00000H to FFFFFH.

8086 Microprocessor Key Features

Beyond its address bus, the 8086 microprocessor has several other defining characteristics:

• It is a 16-bit microprocessor, meaning its data bus is 16 bits wide, allowing it to process 16 bits of data at a time.
• It has a 20-bit address bus, enabling it to access 1 MB of memory.
• It was introduced by Intel in 1978.
• It has a powerful instruction set.

Conclusion on 8086 Address Bus Bits

Based on the architecture of the 8086 microprocessor, its address bus is indeed 20-bit wide. This 20-bit address bus is a fundamental characteristic that defines its memory addressing capabilities and is a key distinguishing feature of the 8086 architecture.