How to boot from a USB HDD

I have a new Packard Bell laptop (the previous one is in for repair). I have taken the olf HDD and inserted it into a USB carrier thing. I would like to have the choice of booting up from either the on board HDD or the USB HDD to access apps and data from both. I am assuming that the USB HDD will have all of the bits and pieces to allow this, but I am being put through a rigmarole of repair etc. I have changed the BIOS to have the USB HDD as the primary boot device. Any other tips much appreciated.
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DarinTCHSenior CyberSecurity EngineerCommented:
the old HD is best setup as a slave to the new system
Unless it has all the files and registry bits for the new laptop or unless the new laptop is the exact model of the older laptop you will probably have issues.
Boot from the new and just plug in the old
you can still access the older HD and the data and the apps from it

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I don't believe you can successfully boot Windows off a USB device without some special measures. This is because the USB systems in Windows are re-initialised part way through the boot sequence in order to detect PnP devices, at which point you lose your boot device.

There are some USB boot hacks around that seek to address this, with varying degrees of success. I gave up, personally !
at bootup select startup options and choose USB device.
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