An MD5 checksum is a signature computed from a file's contents. Two identical files share the same checksum; a single differing byte changes it completely. It is the only reliable way to know whether the bios you just downloaded is the one the emulator expects.
For bios files, start with the built-in bios manager:
START→BIOS CHECKING. It automatically verifies the checksum of every file inshare/biosand tells you which ones are missing or wrong. The manual check described here is mostly useful to inspect a file before copying it onto the Recalbox.
Open PowerShell.
Run:
Get-FileHash "C:\path\to\file.bin" -Algorithm MD5
To check every file in a folder, including its subfolders, move into it then run:
Get-ChildItem -Recurse | ForEach-Object { Get-FileHash $_.FullName -Algorithm MD5 } | Select-Object Path, Hash | Format-Table -AutoSize
HashCheck Shell Extension adds a Checksums tab to any file's properties: a right click is all it takes, no command line.
Open a terminal and type:
md5sum /path/to/file.bin
On macOS, the native command is called md5:
md5 /path/to/file.bin
Tip: in the Terminal, type md5sum then drag the file from Finder or your file manager — the path types itself.
To check a whole folder:
find . -type f -exec md5sum {} \;
The computation gives you a 32-character string, for example a860e8c0b6d573d191e4ec7db1b1e4f6. Compare it against the reference checksum:
.dat file — see clrmamepro or RomCenter, which perform that comparison across thousands of files at once.Checksums are not compared "roughly": either they match exactly, or the file is the wrong one.
Romset
.datfiles often use CRC32 or SHA-1 rather than MD5. Rom management tools handle all three: one more reason to let them verify an entire collection for you.