A checksum is a fingerprint of a file: change a single bit and the fingerprint changes completely. In BIOS work, checksums answer three practical questions. Did two reads of the chip give the same data? Did a download arrive intact? Is the file I am about to write the one I think it is? This tool calculates the common checksums in your browser — the file is never uploaded.

How to use it

  1. Choose the file: a dump you read from a chip, a file you downloaded, or any other file.
  2. Wait a moment for large files; a 16 MB dump takes about a second.
  3. Read the size, CRC32, SHA-256 and SHA-1, the share of blank bytes and the first 16 bytes.

The tool also points out two useful facts about firmware files: whether the file starts with an Intel flash descriptor (a full SPI image), and whether it is entirely 0xFF or 0x00 — the signature of an erased chip or a failed read.

Which checksum to use

  • SHA-256 — the standard for comparing files; practically impossible to fake by accident.
  • SHA-1 — still common in older listings and tools.
  • CRC32 — short and quick to compare by eye; many programmer applications display it.

Compare like with like: a SHA-256 can only be checked against a SHA-256.

Worked example: read twice, compare

Before writing anything to a BIOS chip, read it twice and compare. Two reads of a chip on a healthy clip connection give identical checksums. If the SHA-256 values differ, the clip is not making reliable contact or the chip's supply is unstable, and neither read can be trusted. The full backup routine is in How to Back Up the Original BIOS Before Flashing; to see where two reads differ, use BIOS Dump Compare Tool.

Reading the extra checks

  • "Every byte is 0xFF" — the file is blank: an erased chip, or a read with the clip on the wrong pins.
  • "Every byte is 0x00" — almost always a failed read: no contact, wrong voltage or wrong chip selected.
  • "Intel flash descriptor signature at 0x10" — the file is a full SPI image beginning with the descriptor, as described in The Intel Flash Descriptor: Regions, Locks and Why It Matters.
  • "_FVH found" — the file contains UEFI firmware volumes.

FAQ

Is my file uploaded anywhere?

No. The calculation runs in your browser, and the page never sends the file.

Why do two reads of the same chip have different checksums?

A bad connection or unstable power during reading. Reseat the clip, check the voltage and read again.

Can a checksum tell me the dump is for my board?

No — only that two files are identical. Board match depends on the source and the contents.