The REG COMPARE command.

REG.EXE, built into Windows XP, Windows Server 2003, and later operating systems, or installed from the Windows 2000 Support Tools, has a COMPARE command.

When you type: REG COMPARE /?, you receive:

REG COMPARE KeyName1 KeyName2 [/v ValueName | /ve] [Output] [/s]  KeyName    [\Machine\]FullKey    Machine  Name of remote machine - omitting defaults to the current machine             Only HKLM and HKU are available on remote machines    FullKey  ROOTKEYSubKey             If FullKey2 is not specified, FullKey2 is the same as FullKey1    ROOTKEY  [ HKLM | HKCU | HKCR | HKU | HKCC ]    SubKey   The full name of a registry key under the selected ROOTKEY  ValueName  The value name, under the selected Key, to compare             When omitted, all values under the Key are compared  /ve        compare the value of empty value name   /s         Compare all subkeys and values  Output     [/oa | /od | /os | /on]             When omitted, output only differences    /oa      Output all of differences and matches    /od      Output only differences    /os      Output only matches    /on      No outputReturn Code:  0 - Succussful, the result compared is identical  1 - Failed  2 - Successful, the result compared is differentExamples:  REG COMPARE HKLMSoftwareMyCoMyApp HKLMSoftwareMyCoSaveMyApp    Compares all values under the key MyApp with SaveMyApp  REG COMPARE HKLMSoftwareMyCo HKLMSoftwareMyCo1 /v Version    Compares the value Version under the key MyCo and MyCo1  REG COMPARE \ZODIACHKLMSoftwareMyCo \. /s    Compares all subkeys and values under HKLMSoftwareMyCo on ZODIAC    with the same key on the current machine