Word Size Identification — Valid Widths Which of the following is not commonly used as a processor word size in mainstream computing contexts?

Difficulty: Easy

Correct Answer: 28

Explanation:


Introduction / Context:
Word size refers to the typical width of the CPU internal registers and the size the processor handles efficiently. Recognizing common widths helps when reading ISA specifications and ABI documentation.


Given Data / Assumptions:

  • Common word sizes historically include 16, 32, and 64 bits.
  • Bytes are 8 bits but usually not called a word in mainstream usage.
  • Exotic or niche machines may vary but standards dominate practice.


Concept / Approach:
Identify which of the listed values is not a typical standard word width across common architectures. While 8, 16, and 64 all have roles in terminology or extended word concepts, 28 is unusual and not standardized as a word size in mainstream ISAs.


Step-by-Step Solution:
1) 16 and 64 are widely recognized as word and double word sizes in many ISAs.2) 8 is the byte size; though not a word, it is a standard width term.3) 28 is not a common register or bus width for word definitions.4) Therefore 28 is not a typical word size.


Verification / Alternative check:
Survey mainstream ISAs such as x86, ARM, RISC-V, MIPS: none define 28-bit word sizes as a norm.


Why Other Options Are Wrong:

  • 64: Common in 64-bit architectures.
  • 16: Canonical word size in many legacy systems.
  • 8: Standard byte size; although not called a word, it is a recognized fundamental size.


Common Pitfalls:
Equating byte and word terminology; overlooking that architectures may define word differently but still not use uncommon values like 28.


Final Answer:
28

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