OK after disabling the automatic reboot, I saw that the BSOD is with the dreaded stop code 0x7B. I am familiar with this, so on the laptop that boots fine, I just applied my great old usb_all.reg that changes important USB-related registry entries (usbehci, usbohci, usbuhci, usbccgp, usbhub, USBSTOR). Afterwards,
now Windows 7 boots fine on both laptops from USB HDD !
Note that depending on the hardware, you are asked to reboot once to update the ACPIPIC/ACPIAPIC device (other drivers like network, sound... are already automatically searched and installed). So this is not 100% "portable" as with my current XP booting from USB HDD using usboot from usboot.org.
The method of usb_all.reg applied for Vista too already, so there is nothing new. usbwatcher.exe method seemingly tries to set to right values in registry, and
karyonix's method seems to create a planned job that does same thing at initial boot time. I don't know why it does not work in my case.
Anyhow, to be sure,
before any reboot, and especially after Windows update or driver update or USB plug-and-play,
remember to apply usb_all.reg. This ensures that no BSOD 0x7B is hit on next boot. If ever you still get it, you have to offline change the registries (using RegEditPE or RegistryLoaderPE ) for these USB-related values (in fact the important key is Start which must be set to 0, usually we got BSOD 0x7B because Windows resets it to 3).
Here is usb_all.reg content:
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbccgp]"DisplayName"="Microsoft USB Generic Parent Driver""Group"="Boot bus extender""ImagePath"=hex(2):5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,64,00,72,\ 00,69,00,76,00,65,00,72,00,73,00,5c,00,75,00,73,00,62,00,63,00,63,00,67,00,\ 70,00,2e,00,73,00,79,00,73,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbccgp\Enum]"0"="Root\\LEGACY_USBCCGP\\0000""Count"=dword:00000001"NextInstance"=dword:00000001[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbehci]"DisplayName"="Microsoft USB 2.0 Enhanced Host Controller Miniport Driver""Group"="Boot bus extender""ImagePath"=hex(2):73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\ 52,00,49,00,56,00,45,00,52,00,53,00,5c,00,75,00,73,00,62,00,65,00,68,00,63,\ 00,69,00,2e,00,73,00,79,00,73,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001"Tag"=dword:00000019[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbehci\Enum]"0"="PCI\\VEN_8086&DEV_24CD&SUBSYS_001F1025&REV_03\\3&18d45aa6&0&EF""Count"=dword:00000001"NextInstance"=dword:00000001[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbhub]"DisplayName"="Microsoft USB Standard Hub Driver""Group"="Boot bus extender""ImagePath"=hex(2):73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\ 52,00,49,00,56,00,45,00,52,00,53,00,5c,00,75,00,73,00,62,00,68,00,75,00,62,\ 00,2e,00,73,00,79,00,73,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001"Tag"=dword:0000001b[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbhub\Performance]"Library"=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,25,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,75,\ 00,73,00,62,00,70,00,65,00,72,00,66,00,2e,00,64,00,6c,00,6c,00,00,00"Open"="OpenUsbPerformanceData""Close"="CloseUsbPerformanceData""Collect"="CollectUsbPerformanceData""InstallType"=dword:00000001"PerfIniFile"="usbperf.ini""First Counter"=dword:00000d60"Last Counter"=dword:00000d82"First Help"=dword:00000d61"Last Help"=dword:00000d83[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbhub\Enum]"0"="Root\\LEGACY_USBHUB\\0000""Count"=dword:00000005"NextInstance"=dword:00000005"1"="USB\\ROOT_HUB\\4&b71b443&0""2"="USB\\ROOT_HUB\\4&1b0914a3&0""3"="USB\\ROOT_HUB\\4&33f1b84&0""4"="USB\\ROOT_HUB20\\4&dd5a51b&0"[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbohci]"DisplayName"="Microsoft USB Open Host Controller Miniport Driver""Group"="Boot bus extender""ImagePath"=hex(2):5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,64,00,72,\ 00,69,00,76,00,65,00,72,00,73,00,5c,00,75,00,73,00,62,00,6f,00,68,00,63,00,\ 69,00,2e,00,73,00,79,00,73,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbohci\Enum]"0"="Root\\LEGACY_USBOHCI\\0000""Count"=dword:00000001"NextInstance"=dword:00000001[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\USBSTOR]"DisplayName"="USB Mass Storage Driver""ImagePath"=hex(2):73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\ 52,00,49,00,56,00,45,00,52,00,53,00,5c,00,55,00,53,00,42,00,53,00,54,00,4f,\ 00,52,00,2e,00,53,00,59,00,53,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001"Group"="Boot bus extender""Tag"=dword:00000008[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\USBSTOR\Enum]"0"="Root\\LEGACY_USBSTOR\\0000""Count"=dword:00000002"NextInstance"=dword:00000002"1"="USB\\VID_067B&PID_2506\\0"[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbuhci]"DisplayName"="Microsoft USB Universal Host Controller Miniport Driver""Group"="Boot bus extender""ImagePath"=hex(2):73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\ 52,00,49,00,56,00,45,00,52,00,53,00,5c,00,75,00,73,00,62,00,75,00,68,00,63,\ 00,69,00,2e,00,73,00,79,00,73,00,00,00"ErrorControl"=dword:00000001"Start"=dword:00000000"Type"=dword:00000001"Tag"=dword:00000018[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbuhci\Enum]"0"="PCI\\VEN_8086&DEV_24C2&SUBSYS_001F1025&REV_03\\3&18d45aa6&0&E8""Count"=dword:00000003"NextInstance"=dword:00000003"1"="PCI\\VEN_8086&DEV_24C4&SUBSYS_001F1025&REV_03\\3&18d45aa6&0&E9""2"="PCI\\VEN_8086&DEV_24C7&SUBSYS_001F1025&REV_03\\3&18d45aa6&0&EA"