Generally it is easier to install Windows first, then Debian, but of course it is possible the other way round. The Debian boot manager can be configured to respect the Windows installation, the Windows boot manager does not know anything about other operating systems, so you should leave that to Debians tools, usually GRUB. You can also select the OS to be booted in most (?) UEFI settings implementations.
The Debian installer is capable of resizing existing Windows installations, to make room for Debian. You should keep a Debian Live USB stick around, because Windows still sets the MS boot manager as default under some circumstances. Alternative would be to select the boot device from UEFI settings as mentioned and then fix the problem from the installed Debian. To get GRUB to know about Windows OS, you need the package os-prober. I am not sure if this is automatically installed by the installer, if it detects Windows. If not, install it later. Note that os-prober will probably get deactivated in the next Debian release for some security concerns, AFAIK it is not yet decided, how this will be finally handled and if there will be an alternative mechanism. If you can choose between UEFI and BIOS (legacy) mode, I would recommend UEFI, it simplifies booting and has probably other advantages too. I use UEFI with disabled secure boot. It is possible to use secure boot with Debian, but you have to actively care for key handling and signing of kernels and modules which you compile yourself then. Another alternative to your plan might be to run the Windows installation in one of the many available VM solutions. This works very well, except for accelerated video (no option if you want to play games or use special streaming software which is only available for Windows). Hope that helps, Christian On 2022-04-30 13:50 UTC+0200, Richard Owlett wrote: > I will be setting up a Windows laptop to dual boot Debian. > If the machine has legacy BIOS, no problem as I've done that before. > > If it is a UEFI machine (possibly with secure boot, what should I be > reading. > > TIA > -- http://www.cb-fraggle.de