Historical microprocessors — data bus width of the first commercial CPU Identify the data bus width of the first commercial microprocessor introduced (e.g., Intel 4004).

Introduction / Context:
The evolution of microprocessors began with very modest word sizes. Knowing the data bus width of the earliest commercial CPU helps place later 8-bit and 16-bit families in historical context and illustrates why early systems focused on simple calculators and control tasks.

Given Data / Assumptions:

• “First microprocessor” refers to the early commercially available CPU-on-a-chip, exemplified by the Intel 4004.
• Data bus width is the number of bits transferred in parallel for data.

Concept / Approach:
The Intel 4004 used a 4-bit data path aligned with its original application in desktop calculators, where decimal digits could be conveniently represented as binary-coded decimal (BCD) nibbles. This constrained width simplified the architecture and transistor count of the first-generation microprocessor, paving the way for subsequent 8-bit (8080/8085) and 16-bit (8086) designs.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer literature and textbooks consistently classify the 4004 as a 4-bit microprocessor, while its successors (e.g., 8008/8080) expanded to 8 bits.

Why Other Options Are Wrong:

• 1-bit/2-bit: too narrow and not representative of the 4004.
• 8-bit/16-bit: later generations, not the first commercial CPU-on-a-chip.

Common Pitfalls:

• Confusing CPU “word size” with address bus width or instruction length; the earliest device was unequivocally 4-bit in data handling.

Final Answer:
4-bit data bus