MD5 hashes are a way of verifying that your file is the correct one and/or that it's not corrupt. There's a few ways to check; for Windows users, try using WinMD5.

PS1 BIOS:
SCPH1001.BIN: 924e392ed05558ffdb115408c263dccf
SCPH101.BIN: 6e3735ff4c7dc899ee98981385f6f3d0
SCPH5000.BIN: eb201d2d98251a598af467d4347bb62f
SCPH5500.BIN: 8dd7d5296a650fac7319bce665a6a53c
Scph5502.bin: e56ec1b027e2fe8a49217d9678f7f6bb
Scph7000.bin: 8e4c14f567745eff2f0408c8129f72a6
scph7502.bin: b9d9a0286c33dc6b7237bb13cd46fdee
Scph7003.bin: 490f666e1afb15b7362b406ed1cea246
SCPH7001.BIN: 1e68c231d0896b7eadcad1d7d8e76129

PS2 BIOS:
PS2 Bios 30004R V6 Pal.bin: 28922c703cc7d2cf856f177f2985b3a9
PS2 Bios 30004R V6 Pal.MEC: 3faf7c064a4984f53e2ef5e80ed543bc
PS2 Bios 30004R V6 Pal.NVM: ea592129bf0c9189cafe772657261148
rom1.bin: 44552702b05697a14ccbe2ca22ee7139
scph10000.bin: acf4730ceb38ac9d8c7d8e21f2614600
scph10000.NVM: 0f343b0931126a20f133d67c2b018a3b
scph39001.bin: d5ce2c7d119f563ce04bc04dbc3a323e
scph39001.MEC: 3faf7c064a4984f53e2ef5e80ed543bc
scph39001.NVM: 0639a9ff5f5f3fd7833b924b9d97a8ae
SCPH-70004_BIOS_V12_PAL_200.BIN: dc752f160044f2ed5fc1f4964db2a095
SCPH-70004_BIOS_V12_PAL_200.EROM: 9feb1fdeadd6232a13b95e60b34ccef9
SCPH-70004_BIOS_V12_PAL_200.NVM: 5195b9111609959d3a20e2fb9527edbd
SCPH-70004_BIOS_V12_PAL_200.ROM1: 82dc50fa18e636850f557c4ea66c7bfd
SCPH-70004_BIOS_V12_PAL_200.ROM2: 82dc50fa18e636850f557c4ea66c7bfd

Dreamcast BIOS:
DC - BIOS (All).bin: d407fcf70b56acb84b8c77c93b0e5327
DC - BIOS.bin: e10c53c2f8b90bab96ead2d368858623
DC - Flash (All).bin: 93a9766f14159b403178ac77417c6b68
DC - Flash.bin: 0a93f7940c455905bea6e392dfde92a4
DC - Utopia CD Loader V1.1.cdi: 965014e4ea7247c24c8a746d2a219df7
DC - Utopia CD Loader V1.1.nrg: 70a3385cb638912f8637a8f1e9300727
DC - VMS BIOS (Full).bin: 4bffb9b29b9aeb29aa618f3891a300ce