De acordo com a Microsoft, no link e outros:
GDR service branches contain only those fixes that are widely
released to address widespread, critical issues. LDR service
branches contain hotfixes in addition to widely released fixes.
Para o Windows 7 e amp; Server 2008, estes são:
6.1.7600.16xxx Windows 7 and Windows Server 2008 R2 RTM GDR
6.1.7600.20xxx Windows 7 and Windows Server 2008 R2 RTM LDR
6.1.7601.17xxx Windows 7 and Windows Server 2008 R2 SP1 GDR
6.1.7601.21xxx Windows 7 and Windows Server 2008 R2 SP1 LDR
Portanto, para versões X86 do Win7 - dependendo dos hotfixes instalados - você pode ter qualquer um dos seguintes:
Ntoskrnl.exe 6.1.7600.17207 3,902,312 05-Jan-2013 05:02
Ntoskrnl.exe 6.1.7600.21417 3,915,112 05-Jan-2013 04:53
Ntoskrnl.exe 6.1.7601.18044 3,913,064 05-Jan-2013 05:00
Ntoskrnl.exe 6.1.7601.22210 3,916,648 05-Jan-2013 04:49