Interpreting POST codes: On classic IBM-PC–style systems, a POST code in the 2xx range generally indicates a problem with which subsystem?

Introduction / Context:
Power-On Self-Test (POST) uses numeric codes to report failures before the screen, keyboard, and drives are reliably available. Understanding the general meaning of code ranges speeds diagnosis when only beeps or hex codes are shown.

Given Data / Assumptions:

• Classic IBM-PC/AT–style POST conventions are assumed.
• We are mapping the 2xx range to a subsystem category.
• The goal is a quick triage, not a vendor-specific microcode list.

Concept / Approach:

While exact mappings vary by BIOS vendor, many legacy references associate 2xx POST codes with memory subsystem checks, including RAM presence, addressing, and sometimes ROM checksum conflicts within that broader initialization phase. Practically, a 2xx code focuses attention on memory integrity and related low-level firmware validation close to memory tests.

Step-by-Step Solution:

Verification / Alternative check:

Cross-check with motherboard documentation for the exact BIOS (AMI, Award, Phoenix). Even when tables differ, 2xx almost always points near the memory test stage of POST.

Why Other Options Are Wrong:

• Hard drive: typically tested later, after controller init.
• System board (generic): too broad and not specifically signaled by 2xx in most lists.
• Second adapter card: adapter issues usually present as later bus initialization faults.
• CMOS battery: low battery results in configuration loss, not a dedicated 2xx fault.

Common Pitfalls:

Relying on a single universal table when vendors differ; failing to isolate by removing all but essential hardware; overlooking bent DIMM pins or mixed timings that pass intermittently.

Final Answer:

RAM or ROM