BIOS files arrive with half a dozen extensions, and the extension says surprisingly little about what is inside. A .bin might be a full chip dump or only the BIOS region; a .cap may be an Asus update with a header in front; an .exe from a vendor's website may hide a perfectly usable image. Knowing what each file really is decides whether you can write it to a chip as it is, need to extract something from it, or should not use it at all.
Two kinds of BIOS file
Every BIOS file falls into one of two groups:
- Full chip images — an exact copy of the whole SPI flash chip, the same size as the chip (4, 8, 16 or 32 MB), including descriptor, ME region and board data on Intel systems. These are what a programmer reads and writes.
- Update packages — files made for the vendor's update tool. They may contain only the BIOS region, sometimes the ME and EC updates, often wrapped in a header, a capsule format or an executable. They are not meant for a programmer.
The first question for any file is therefore: is it exactly the size of my chip? If yes, it is probably a full image. If not, it is probably an update package or a single region.
Extensions you will meet
| Extension | What it usually is | Programmer-ready? |
|---|---|---|
.bin | Full chip dump from a programmer, or a single region | Often, if the size matches the chip |
.rom | Full image or BIOS region, depending on who made it | Sometimes |
.cap | Capsule update (Asus and others): image with a header | After removing the header, sometimes |
.fd | Firmware volume or BIOS region from UEFI builds | Usually only part of a full image |
.F1, .F2, .10, .1A0 | Desktop vendor updates (Gigabyte, ASRock, MSI) | Often the BIOS region, sometimes full |
.exe | Vendor update utility with the image packed inside | No — extract first |
.hdr, .wph, .fl1 and others | Vendor-specific update packages | No — extract first |
These are tendencies, not rules. Always check size and content.
Checking what you have
Size
Compare the file size with the chip capacity in bytes:
- 4 MB = 4,194,304 bytes
- 8 MB = 8,388,608 bytes
- 16 MB = 16,777,216 bytes
- 32 MB = 33,554,432 bytes
An exact match suggests a full image. A file a little larger than a power of two often has a header (common with capsule files). A smaller file is usually a region or a compressed package.
Structure
Open the file in UEFITool or a similar image viewer. A full Intel image shows a descriptor followed by regions: ME, BIOS and sometimes GbE. A region-only file shows firmware volumes but no descriptor. An update package may not open at all.
Strings
Search in a hex editor for the board's model name, the BIOS version and vendor strings. They tell you which machine the file belongs to — and whether it carries another machine's serial number, which matters for the reasons explained in BIOS Dump vs Clean BIOS: What's the Difference.
Getting a usable image from an update package
When you only have the vendor's update, you can often still build a full image:
- Extract the package. Many vendor executables are self-extracting archives that a good archiver opens, or have a command-line option to unpack. Community tools exist for several vendors' formats.
- Locate the BIOS region inside the extracted files — usually the largest file, often with a clear name.
- Remove any header if the file is slightly larger than expected; capsule files typically have a header of a few kilobytes in front of the image.
- Insert the region into your own full image. Take your board's original dump (read with a programmer), and replace only its BIOS region with the one from the update. Your descriptor, ME region and identity data stay intact.
- Verify the result before writing — How to Verify a BIOS File Before Flashing lists the checks.
This route is often better than downloading someone else's full dump, because the BIOS region comes from the vendor and everything else from your own board.
Example: building an image from a vendor update
A laptop's BIOS region is corrupted; the rest of the chip reads fine. The catalog has no full image for the board, but the vendor's website offers the latest BIOS update as an executable.
- The executable opens in an archiver and reveals several files, including one about 12 MB in size with the platform name in it — the BIOS region and a capsule header.
- UEFITool shows the header and the firmware volumes inside. The technician extracts the BIOS region body without the header.
- The board's original dump, read twice and verified, is opened in the same tool. Its descriptor shows the BIOS region size, which matches the extracted region exactly.
- The extracted region replaces the BIOS region of the original dump. The descriptor, ME region and identity data remain the board's own.
- A binary compare confirms that only the BIOS region changed. The image is written and verified, and the laptop boots with the newest firmware and its original serial number.
This is often the cleanest result possible: vendor firmware, the board's own data, nothing from anyone else's machine.
Desktop motherboards
Desktop vendors usually provide update files that their built-in flash tools accept directly from a USB stick. Many of these files are full images or nearly full images for the chip, and some boards accept them through built-in recovery features without a programmer. When you do use a programmer, check sizes the same way: a desktop update file that matches the chip size can usually be written, after you have backed up the original.
EC firmware files
Archives labelled "BIOS & EC" or "BIOS + KBC" contain two images: one for the BIOS chip, one for the EC. EC images are much smaller — often 64 KB to 1 MB, depending on the EC — and must go to the EC's own flash, never to the BIOS chip. Mixing them up is a classic mistake. EC storage is explained in EC/KBC Firmware: The Second BIOS in Your Laptop.
Naming your own files
Whatever you download, rename working copies so you know what they are:
LA-D312P_full-image_16MB_from-vendor-v1.15_with-own-ME_2026-10-21.bin
It looks long, but six months later you will know exactly what you wrote to that board.
FAQ
Can I write a .cap file directly with a programmer?
Not as it is, in most cases. The capsule header in front of the image shifts everything. Remove the header with a tool that understands the format, or use the vendor's own flashing method.
Is a .rom file the same as a .bin file?
Only by convention. Both are raw binary data; the contents depend on who made the file. Check the size and structure.
Why is my BIOS file smaller than the chip?
It probably contains only the BIOS region. It needs to be combined with the descriptor, ME and other regions from a full image before writing.
Can I flash a vendor update file from the BIOS setup on a dead laptop?
Not on a dead laptop. On a working one, the vendor's built-in update function is the right way to use those files.
Which file should I prefer from the catalog?
A full image for your exact board code and revision, ideally one with a clean ME region, which you then personalise with your board's identity data from your own backup.
Bottom line
Extensions are hints; size and structure are facts. Full images match the chip size exactly and can be written after preparation; update packages need extracting, and their BIOS region is best combined with your own board's original image. Check every file before it goes near a chip, and keep each working file clearly named. For the meaning of a raw bios dump versus a prepared image, see the glossary.