Checksums tell you whether two files are identical; this tool tells you where they differ. That matters at two moments in BIOS repair: when two reads of the same chip do not match, and when you want to see what changed between an original dump and a modified or clean one. Both files are read locally in your browser; nothing is uploaded.
How to use it
- Choose the first file — for example the first read of a chip.
- Choose the second file — the second read, or the file you are comparing against.
- Read whether they are identical, how many bytes differ, and the list of differing address ranges.
Nearby differences (within 16 bytes of each other) are grouped into one region, so a changed block shows as a single range rather than hundreds of single bytes.
Interpreting the result
| What you compare | What to expect |
|---|---|
| Two reads of the same chip | Identical. Any difference means an unreliable read. |
| Original dump vs a clean BIOS for the same board | Differences in the ME region, NVRAM and areas holding serials, UUID and MAC |
| Dump before and after a BIOS settings change | Small differences in the NVRAM area |
| Two different board revisions | Large differences throughout |
Worked example: unreliable reads
Two reads of a 16 MB chip differ in 37 bytes spread across a dozen regions, at seemingly random addresses. Real data changes would cluster in a few areas; scattered single-byte differences point at a connection problem. After cleaning the chip's legs and reseating the clip, two new reads are identical. Only then is the dump trustworthy enough to keep as the original backup, as explained in How to Back Up the Original BIOS Before Flashing.
Worked example: what a clean BIOS changes
Comparing a board's original dump with a downloaded clean file of the same size, the differences gather in a large block early in the file and a few small areas later. Using the board's flash layout, the large block falls in the ME region, and the small ones contain the serial number and LAN MAC address. Those small areas are exactly what must be carried over from the original, as covered in Serial Number, UUID and MAC Address in BIOS: How to Preserve Them. Addresses can be converted with Hex, Decimal and Binary Converter.
FAQ
Are my files uploaded?
No. Both files are read and compared in your browser.
Why do my two reads differ only slightly?
Unreliable contact or power during reading. Scattered single-byte differences are typical; reseat and read again.
Can I compare files of different sizes?
Yes. Bytes beyond the end of the shorter file count as different, and the result notes the size difference.