Troubleshooting SIMMs – capacity misreporting A 64-Mbyte SIMM is installed, but a memory test detects it as only 32-Mbyte. Which fault best explains this symptom in digital hardware troubleshooting?

Introduction / Context:
When system firmware or diagnostic tools report half of an expected memory capacity, it often indicates an addressing issue rather than a complete module failure. Understanding how address lines map the accessible space helps quickly isolate the fault.

Given Data / Assumptions:

• Expected capacity: 64 MB; observed: 32 MB.
• Module is otherwise detected and operates at least partially.
• Modern SIMMs map capacity by address line decoding across chip banks.

Concept / Approach:
If a most significant address (MSA) line is stuck at 0 or 1, the system can only access half the address space because it cannot toggle into the higher or lower half. Therefore the reported capacity becomes 1/2 of the true size. This is a classic symptom of a stuck MSB address line or a break in the address path.

Step-by-Step Solution:

Verification / Alternative check:
Technicians often probe the address bus or perform boundary tests that flip the high address bit. If content mirrors every 32 MB block, it indicates the MSB cannot change state, confirming the diagnosis.

Why Other Options Are Wrong:

• Not installed properly: Often results in no detection, intermittent errors, or parity/ECC faults, not a consistent 50% capacity.
• Incorrect voltage: Would likely cause instability or total failure rather than a clean 50% reduction.
• Faulty decoder on the SIMM: Possible but the hallmark symptom of exactly half capacity most directly points to a stuck MS address line in the system or module path.

Common Pitfalls:

• Assuming power issues first; while important, a precise halving is a strong hint of addressing, not power.
• Overlooking simple continuity issues on connectors or traces affecting a single address pin.

Final Answer:
The most significant address line is stuck high or low.