In computer architecture and data manipulation: A number used to control or shape the form of another number (for example by selective bit operations) is called what?

Introduction / Context:
Low-level programming and digital logic often use a special value to clear, set, or test selected bits of another value. Recognizing the correct terminology is essential for understanding bitwise operations and systems programming.

Given Data / Assumptions:

• The operation is numerical but focuses on bits.
• The controlling value determines which bits pass through, are set, or are cleared.
• Common operations include AND, OR, XOR, and NOT.

Concept / Approach:

A bitmask, or simply mask, is a number whose bits are used to select or modify bits in another number. For example, AND with 0 clears a bit; OR with 1 sets a bit. Thus the controlling number is called a mask.

Step-by-Step Solution:

Verification / Alternative check:

Example: To zero the lower 4 bits of 0xAB (10101011), AND with 0xF0 (11110000). The value 0xF0 is the mask controlling the operation.

Why Other Options Are Wrong:

• Map: refers to associations, not bit control.
• Marker: annotation concept, not a numeric controller.
• Modulo: arithmetic operator for remainders, not bit selection.
• None of the above: incorrect because 'Mask' is exact.

Common Pitfalls:

• Confusing 'mask' with 'map' due to similar spelling.
• Assuming masking only means hiding; in computing it is precise bit manipulation.

Final Answer:

Mask.