Hi - I have windows on my primary nvme and want to install slackware 15 on second. This is a uefi laptop. After fresh install of slack or re-running of elilo my bios finds the slackware entry. after I boot into windows - windows seems to overwrite the efi wiping out my slack entry causing me to use a boot disk to get back into slack. i tried changing slack drive to mbr and reinstalling but the installer still finds the efi partition and opts to use that. i also tried creating an efi on the second drive but neither slack or bios sees this.

caveat - i replaced the old second drive pop-os with a new nvme. pop and windows seemed to comingle fine. windows was the default boot and if i esc into bios i could always find pop (actually showing me the name of the second drive - not pop entry per se) - selecting the second drive booted into pop no problem. How do i get this same function with slack?

Do i need to reset bios somehow to address the drive replacement?

Other than using a boot disk is there a better way to install Slackware that i can permanently access it via bios (even through kernel upgrades)?

As far as I know, you can only have 1 efi partition on any UEFI system. Its the UEFI that has changed the NVRAM entry for Slack that has beed screwed up. I found this out the hard way also, but not with Win. My desktop is UEFI, I have 3 disks. SDA has Slackware current, SDB has Slack 14.2 on a MBR setup and my NMVE drive has Slack 15.0. I also installed ReFind, its a boot manager; can also be a boot loader. To get SDA to boot, I have a separate directory for SDA on nvme0n1p1, the kernel and initrd goes there, and I can boot SDA. I have messed with efibootmgr in slackware. You can display the NVRAM entries the UEFI uses. You can modify the boot order, and change entries. I do not know if Win supplies shuch a program, you can look to see if it is available. It works from Slack with root privlidges.

You need to have a directory on the Win disk to boot Slack.

With my setup, Refind presents a menu and I choose what system I want to boot. It then passes control to the boot entery for the appropriate disk. It works well, you can google for ReFind, it is very well documented.

I'm not sure you need Refind, however, it will help you understanding UEFI, its not BIOS.