Where is the Power-On Self-Test (POST) routine stored that begins by counting system board RAM?

Introduction / Context:
When a PC powers up, firmware runs diagnostic checks known as POST. One visible step is counting system memory. Knowing where these routines are stored clarifies the roles of ROM, CMOS, CPU, and RAM during boot.

Given Data / Assumptions:

• Traditional PC architecture with a firmware chip (legacy BIOS) on the motherboard.
• CMOS holds configuration parameters with a battery.
• CPU executes instructions but does not store firmware code permanently.

Concept / Approach:
POST code is firmware residing in read-only memory (historically ROM, EPROM, or flash), commonly called the ROM BIOS. At reset, the CPU fetches instructions from a fixed address mapped to this firmware, which initializes hardware, counts RAM, and prepares to load the operating system. CMOS only stores settings (e.g., boot order, date/time); RAM is not yet initialized when POST begins and cannot contain the code that initializes itself.

Step-by-Step Solution:

Verification / Alternative check:
Flashing the BIOS updates the firmware image that includes POST routines. Removing the CMOS battery resets settings but does not erase the firmware code, confirming it is stored in ROM/flash.

Why Other Options Are Wrong:

• RAM: Volatile and uninitialized at power-on; cannot contain POST.
• Microprocessor: Executes code but does not store it permanently.
• CMOS: Holds configuration data, not executable firmware.
• 8259: A programmable interrupt controller, not a storage location for POST.

Common Pitfalls:
Confusing CMOS setup utility (a program in ROM) with the CMOS memory that simply stores its settings.

Final Answer:
ROM BIOS