A couple years ago I acquired a new-to-me refurbished Desktop. It came with a 2 TiB hard-drive mostly wasted on Windows 7. At the time I decided to keep Windows 7. (Tax Software and a couple other useful programs ran under it; however, the major brands of Tax Software no longer do). And while I almost always use Puppys, still 2 TiBs would leave a lot of wasted space. So I decided to (a) move Windows restore files and remove its partition; (b) shrink Windows main partition and (c) add two new partitions, one for Puppys, the other for Linux Mint 20 Ulyana. Wasn't sure what I'd do with Ulyana. But you never know. The restructuring went without a hitch. Ulyana's grub enabled booting it and Windows; puppies --although on the hard-drive-- being booted via a dedicated USB-Stick.
I recently decided to upgrade Linux Mint to Vanessa. Still not sure what I'd do with it. Maybe try to convince my wife to abandon Windows 10. And Linux Mint does have some advantages, such as Hypnotix, an IPTV streaming application with support for live TV, movies and series. https://github.com/linuxmint/hypnotix.
Selected 'Custom Install' so that I could keep my Windows 7 and Puppy partitions. But during the installation process I received a notice to the effect "There is no EFI partition so booting will likely fail. Continue at your own risk". Brilliant idea: create a boot-loader for an 'after market' operating system which requires restructuring one's hard-drive, possibly wiping out years of work.
Well I took the risk. And true to its prophecy, booting failed.
Grub2Config to the rescue.
Booted Puppy on a USB-Stick which had grub2config installed. https://www.forum.puppylinux.com/viewto ... 703#p29703. Ran it, selecting sda as the partition for its installation. Rebooted. Its boot menu offered all my puppies, Windows and Linux Mint. All could be booted into.