Which of the following is a classic example of a one address, accumulator based microprocessor architecture?

Introduction / Context:
Instruction set architectures can be classified by how many explicit addresses appear in each instruction. One address architectures are often accumulator based, where most operations implicitly use the accumulator register and specify only one explicit operand. This question asks you to identify a microprocessor that is a classic example of such a one address, accumulator based design.

Given Data / Assumptions:

• We are comparing different Intel processors and coprocessors.
• We focus on instruction format and whether it is accumulator based with one explicit address.
• The question expects knowledge of the programming style and architecture of the 8085 and other devices.

Concept / Approach:
In a one address instruction set, many instructions have an implicit accumulator operand. For example, an instruction may operate on the accumulator and a memory or register operand specified in the instruction. The 8085 microprocessor is a well known 8 bit processor that uses the accumulator heavily. Instructions such as ADD M or ADD B implicitly add to the accumulator. Other architectures, like modern 32 bit processors, provide more general register to register operations with multiple explicit operands.

Step-by-Step Solution:
Step 1: Recall that the 8085 instruction set uses the accumulator as an implicit operand in many arithmetic and logic instructions.Step 2: Recognize that this style is characteristic of one address accumulator based architectures.Step 3: Compare with the 8087 numeric coprocessor, which primarily uses a stack based register file for floating point operations.Step 4: Compare with the 80386 and Pentium class processors, which use more general register addressing with multiple explicit operands.Step 5: Conclude that the 8085 is the classic example requested.

Verification / Alternative check:
Look at sample assembly code. On the 8085, instructions such as ADD B mean accumulator equals accumulator plus register B. The accumulator is not mentioned explicitly in the instruction format, which is typical of a one address design. In contrast, in 80386 assembly, you might write ADD EAX, EBX with both operands explicitly shown. This difference supports classifying the 8085 as the example of a one address, accumulator based architecture.

Why Other Options Are Wrong:
Option B: The 8087 is a numeric coprocessor with a stack oriented register model and is not a classic one address accumulator based microprocessor.Option C: The 80386 is a complex 32 bit microprocessor with rich addressing modes and two operand instructions, not a simple one address architecture.Option D: The Pentium 4 is a much newer superscalar processor with multiple pipelines and general purpose registers, again not a one address accumulator based example.

Common Pitfalls:
Students sometimes confuse the concept of one address instructions with the number of physical address lines. One address refers to the instruction format, not the hardware address bus. Another mistake is assuming that all older processors are one address architectures. While many early microprocessors were accumulator based, others used different styles, so you should always look at the instruction set to be sure.

Final Answer:
The correct answer is Intel 8085 microprocessor, which is largely accumulator based and often uses one address instructions.