Where is the BIOS Stored? - Understanding BIOS Location

Understanding BIOS Storage: A Beginner's Guide

The BIOS, or Basic Input/Output System, can appear complex to those unfamiliar with computer hardware. A common question arises: where exactly is the BIOS located and how is it stored within a computer system?

This article addresses these inquiries, providing clarity for newcomers to the world of computing.

What is the BIOS?

The BIOS serves as the initial software a computer runs when powered on. It's responsible for testing hardware components and loading the operating system.

Understanding its storage location is crucial for troubleshooting and potential updates.

Where is the BIOS Stored?

Traditionally, the BIOS was stored on a ROM chip (Read-Only Memory) located on the motherboard. This meant the BIOS was permanently written and couldn't be easily modified.

However, modern systems predominantly utilize Flash memory, a type of EEPROM (Electrically Erasable Programmable Read-Only Memory).

The Shift to Flash Memory

The transition to Flash memory allows for BIOS updates without physically replacing the chip. This is a significant advantage, enabling manufacturers to release fixes and improvements.

Users can often update their BIOS through software utilities provided by the motherboard manufacturer.

Locating the BIOS Chip

The BIOS chip is typically a small, rectangular component on the motherboard. Its exact location varies depending on the motherboard model.

It's usually labeled with a manufacturer's code and a chip number.

SuperUser Q&A Source

The information presented here originates from a question and answer session on SuperUser, a community-driven Q&A platform that is part of the Stack Exchange network.

SuperUser provides a valuable resource for technical support and knowledge sharing.

Image credit: Richard Masoner / Cyclelicious (Flickr).

Understanding BIOS Storage

A SuperUser user, T..., has posed a question regarding the location and nature of BIOS storage. The inquiry stems from apparent contradictions within the Wikipedia article on BIOS.

The Core of the Question

The Wikipedia entry states that BIOS software resides on a non-volatile ROM chip. However, it also notes that modern systems utilize a flash memory chip, allowing for rewritable BIOS contents. This raises a key question: if ROM is inherently read-only, how can the BIOS be updated?

Furthermore, the user asks whether "flash memory chip" and "non-volatile ROM" are synonymous terms, both referring to the same storage location for the BIOS.

Disambiguating ROM and Flash Memory

The confusion arises from the evolution of technology. Traditionally, BIOS was indeed stored on a read-only memory (ROM) chip. This meant any changes required physically replacing the chip.

However, modern motherboards employ flash memory, a type of electrically erasable programmable read-only memory (EEPROM). While still considered non-volatile – meaning it retains data even without power – flash memory *can* be written to and erased electronically.

A Single Medium, Evolving Technology

Therefore, the BIOS is not stored on two separate mediums. Instead, the storage medium has evolved.

• Initially, it was a true ROM chip.
• Now, it's a flash memory chip, a more advanced form of non-volatile memory.

The term "non-volatile ROM" in the Wikipedia article is somewhat of a generalization. It accurately describes the *function* – persistent storage – but doesn't specify the underlying technology.

Implications of Flash Memory

The use of flash memory allows for convenient BIOS updates. These updates can add new features, improve compatibility, or address security vulnerabilities.

However, as the article correctly points out, this rewriteability also introduces a potential security risk: the possibility of BIOS rootkits, malicious software that infects the BIOS itself.

In conclusion, the BIOS is currently stored on a flash memory chip, which is a type of non-volatile memory capable of being rewritten, representing an advancement over the original read-only ROM technology.

Understanding BIOS Rewriting and Memory Types

A SuperUser community member, Varaquilex, provides insight into why the BIOS can be rewritten despite being stored on what is traditionally considered read-only memory.

ROM vs. EEPROM and Flash Memory

The term "read-only" concerning the BIOS program refers to the memory's non-volatile nature. This means data is retained even when power is removed, unlike volatile RAM.

However, the BIOS is actually stored on EEPROM (Electrically Erasable Programmable Read-Only Memory) or flash memory, which can be rewritten or updated.

Historically, BIOS updates required physically replacing the chip or sending it to a manufacturer for reprogramming. Modern EEPROMs allow for electrical rewriting without chip removal.

Flash Memory and Non-Volatile ROM: Are They the Same?

According to Wikipedia, flash memory is a non-volatile storage medium capable of electrical erasing and reprogramming.

Flash memory evolved from EEPROM technology. There are two primary types – NAND and NOR – distinguished by their underlying logic gate structures.

• NAND flash is written and read in blocks or pages.
• NOR flash allows individual byte-level writing and reading to erased locations.

While related, EEPROM and flash memory aren't identical. They represent distinct memory types with differing transistor configurations, but both serve as storage for the BIOS program.

BIOS Settings and the CMOS Chip

It’s important to differentiate between the BIOS settings and the BIOS program itself. The settings are stored on a CMOS chip.

This chip is continuously powered by the motherboard battery, explaining why removing the battery resets the BIOS to its default configuration. The core program remains unchanged, but the user-defined settings are lost.

For a comprehensive understanding of memory usage during the boot process, a related discussion can be found in another answer.

CMOS and NVRAM Considerations

Thanks to community member Andon M. Coleman, it’s worth noting that BIOS settings aren't exclusively stored in volatile CMOS memory.

Many embedded systems utilize NVRAM (Non-Volatile RAM) for settings storage. PCs have historically used CMOS due to the existing battery powering the real-time clock, making it a cost-effective solution.

• The use of CMOS is largely a historical artifact.
• It allowed for cheaper volatile memory to be used for system settings.

Further contributions and a complete discussion thread are available on Stack Exchange. Feel free to share your thoughts and insights in the comments section.