Historically, what was a key disadvantage of early Numerical Control (NC) machine tool systems in shop-floor operation?

Introduction / Context:
Early NC systems relied on punched tape and electromechanical readers to load part programs. While NC revolutionized repeatability and precision, the medium and readers introduced fragility on the shop floor, affecting uptime and quality.

Given Data / Assumptions:

• We are considering legacy NC prior to widespread CNC with solid-state storage.
• Physical tapes were subject to wear, dirt, moisture, and misfeeds.
• Readers had mechanical parts requiring frequent maintenance and alignment.

Concept / Approach:
Punched tape is a serial storage medium; errors in holes or feed mechanism cause program faults. Tape splicing or damage leads to toolpath interruptions. Compared to modern CNCs with flash storage and networks, tape reliability was a dominant operational drawback despite the conceptual benefits of NC.

Step-by-Step Solution:
1) Identify the component most failure-prone: tape and reader. 2) Assess other options: machine overheating is not unique to NC; operator staffing depends on operations policy, not NC itself; computer unreliability is not the key historical pain point versus tape. 3) Choose the disadvantage tied to the tape subsystem.

Verification / Alternative check:
Manufacturing histories frequently cite tape tears, misreads, and feed issues as daily headaches prompting the move to DNC/CNC storage and later to networked program transfer.

Why Other Options Are Wrong:
Option A: Early controllers had limits but were not the primary failure mode compared to tape mechanics.
Option C: Staffing patterns vary; this is not a definitive disadvantage of NC itself.
Option D: Overheating relates to cutting parameters and cooling, not intrinsic to NC technology.
Option E: Invalid since a clear disadvantage is known.

Common Pitfalls:
Assuming modern CNC reliability retroactively applies to tape-based NC; medium mechanics were the weak link.

Final Answer:
The tape and tape reader are not reliable