Most laptops keep their firmware in one SPI flash chip. Some, particularly boards from a certain period of Intel platforms, split it across two chips — for example an 8 MB chip and a 4 MB chip together holding a 12 MB image. To the chipset they appear as one continuous memory space; to a technician with a programmer they are two separate chips that must each be read and written correctly. Getting the order or the split point wrong produces a board that never starts. This guide explains how split images work and how to handle them safely.
Why firmware is split
When a platform's firmware grew beyond the size of a single affordable chip, or a designer chose two smaller chips for cost or availability, the chipset's ability to address two flash components allowed the image to span both. The chipset sees:
- component 0 — the first chip, starting at address 0;
- component 1 — the second chip, continuing where the first ends.
The flash descriptor at the beginning of component 0 describes both chips' sizes and the regions spread across them. The descriptor is explained in The Intel Flash Descriptor: Regions, Locks and Why It Matters.
How to recognise a two-chip board
- Two SPI flash chips near the chipset or EC, often of different sizes.
- In the schematic, two flash chips sharing clock and data lines but with separate chip-select signals.
- A BIOS image for the board whose size equals the sum of two chip sizes, such as 12 MB.
Not every board with two flash chips splits its BIOS: some have a separate chip for the EC firmware or for another controller. The schematic tells you which chip serves which function.
Which chip is first
The order is set by the chip-select lines, not by size or position on the board:
- the chip on the chipset's first chip-select is component 0 — it holds the start of the image, including the descriptor;
- the chip on the second chip-select is component 1 — it holds the rest.
Check the schematic for the chip-select net names. Many boards put the larger chip first, but do not assume it.
Reading a two-chip board
- Identify both chips and their sizes from their markings.
- Read component 0 twice and compare checksums.
- Read component 1 twice and compare checksums.
- Save both reads with clear names — board code, chip position, size, date.
- If you need a combined image, join them in order: component 0 first, then component 1.
Standard reading practice applies to each chip; see How to Read and Write a BIOS Chip with a CH341A Programmer and How to Back Up the Original BIOS Before Flashing.
Splitting a combined image
When you have a single image for the whole board — for example a 12 MB file — and need to write it to an 8 MB chip and a 4 MB chip:
- Confirm the total size equals the sum of the chips exactly.
- Take the first part, equal to component 0's size, for the first chip.
- Take the remaining part for the second chip.
- Check each part's size matches its chip exactly.
The split point is the size of component 0 in bytes — for an 8 MB chip, 8,388,608 bytes, which is 0x800000. Converting offsets is easy with the Hex, Decimal and Binary Converter.
Writing a two-chip board
- Write each chip with its own part of the image, and verify each.
- If only one chip is corrupted and the other is fine, you may need to write only that one — but make sure both parts come from consistent images. Mixing a component 0 from one version with a component 1 from another can break the board.
- Keep the board's unique data — serial numbers, MAC address, licensing data — from the original reads.
When only one chip is readable
Sometimes one of the two chips is damaged or cannot be read reliably. Save whatever you can from both. The first chip usually holds the descriptor and the board-specific regions, which are the most valuable; the second chip often holds the remainder of the BIOS code, which can be taken from a clean image for the same board and version.
Combined images and their sizes
Combined images for two-chip boards have sizes that do not match any single chip, such as 12 MB or 6 MB. That confuses people into thinking the file is wrong or needs padding. It does not; it needs splitting. General rules for matching images to chips are in 8 MB, 16 MB or 32 MB: Matching the BIOS Dump to the Chip.
Tools for splitting and joining
Splitting and joining are simple byte operations, and any reliable tool will do:
- programmer software that can save a selected range of a buffer to a file;
- a hex editor that can select a range by offset and size and save it;
- command-line tools that copy a number of bytes from a file, available on every operating system.
Whatever you use, check the result's size in bytes, and compare the joined image with the original combined file to confirm they are identical before writing anything.
Labelling and storing two-chip images
Two-chip boards double the chance of mixing files up. Name every file with the board code, the chip's position (first or second chip-select), its size and the date, and keep the pair together in one folder. When you store a combined image, note the split point next to it. A year later, those notes are what let you recover the same model quickly.
Symptoms of a two-chip problem
| Symptom | Possible cause |
|---|---|
| Dead board after writing a combined image to one chip | Image not split; second chip not written |
| Board starts but behaves oddly, settings lost | Second chip from a different version |
| Programmer reports wrong size on one chip | That chip is component 1 and smaller |
| Board dead after swapping chips | Component order reversed |
Example: a 12 MB file and two chips
A dead board has an 8 MB and a 4 MB flash chip. The downloaded image is 12,582,912 bytes — exactly 8 MB plus 4 MB. The schematic shows the 8 MB chip on the first chip-select. The technician first reads both chips and saves them; the first chip's read shows a corrupted area in the BIOS region. The first 8,388,608 bytes of the downloaded image are taken for the 8 MB chip, after transferring the board's serial and MAC from the original read, and the remaining 4,194,304 bytes for the 4 MB chip. Both are written and verified. The board starts.
FAQ
How do I know which chip is first?
From the chip-select lines in the schematic. The chip on the first chip-select holds the start of the image.
Can I write the combined file to the larger chip?
No. It will not fit, and the second chip would not be updated. Split it.
Do both chips need to come from the same image?
Yes. Mixing parts from different versions can stop the board starting.
Why is my BIOS file 12 MB?
It is probably a combined image for a two-chip board. Check the board for two flash chips.
What if the second chip holds EC firmware instead?
Then the board does not split its BIOS. Treat each chip according to its function in the schematic.
Bottom line
Two-chip boards spread one image across two flash chips. Identify both chips and their order from the chip-select lines, read and save each one, split combined images exactly at the first chip's size, write and verify each part, and keep both parts from the same consistent image with the board's own unique data.