So I'm a little late to this but I do things similar to tomscharbach. I had Solus installed first on a m.2 and installed windows on a separate SATA SSD. The BIOS for my Lenovo is not great, so I manage boot entries with efibootmgr in Solus, and it's also set to be my primary boot source. Both are EFI, I have fast boot enabled, and haven't had any issues.

I think the key is having the non-target drive mechanically removed from the mechine before installing the OS. I've done a few machines this way with Solus/Windows and other distros and Windows and haven't run into an issue yet. The only issue I have is sometimes Windows wants to take over as the primary boot, but usually pressing F12 and booting into Solus once fixes that, I don't have to play with boot order in the BIOS.

    I use to do that years ago got in habit when setting up drives to take the ones out not using just so I didnt mess one
    up by being stupid and lose data..lol. Nowdays I have to many computers so I just keep things seperate.If you are only one using it usually not an issue. I even tried those slide in carries on the desktop and just popped in the drive and os I wanted to use but never did find one that took the abuse but that was years years ago maybe those slide carriers have changed if you can still buy them plus they never looked to good.. (Just ramblin..lol)

    Heh... yeah, if removing a drive wasn't a 30 minute ordeal I'd do that, but my case sucks, the placement of my PC sucks, and that's a massive hassle when I'm just trying to play one of the few games that doesn't work on Solus..

    Removing my drives during install would've been smart though. Everything seemed to have worked fine, until this morning when I realized that Windows altered my Data HDD in some way and now Linux can't write to it... so that's gonna be a whole thing to deal with, doesn't look like Windows touched my Solus SSD though so hey, it could've been worse... er, in fact gonna have to make a new post on that (if I can't fix myself first).. it's not just my data drive doing that it seems 😅

      Oh, silly me, I just forgot to disable fast boot in windows, all good! 😃

      CT42 ... a massive hassle when I'm just trying to play one of the few games that doesn't work on Solus

      LOL, but I'm laughing with you. I keep a circa-2017 Windows 10 Dell Inspiron 11-3180 (AMD A-9 with R5 graphics) laptop alive for the sole purpose of playing Red Alert 2 - The Aftermath (circa 1996). Try as I might, I've never been able to get RA2 running on newer Intel CPU/GPU computers, but it runs fine on older AMD computers. I have no idea what I am going to do when that computer dies or Windows 10 EOL comes, but then again I'm 75 so it might not be an issue.

        CT42 I'm just trying to play one of the few games that doesn't work on Solus..

        Have you looked into Stadia? Don't know if you have a Google adversion, but it's what I use to play Destiny on my laptop w/Solus. Works great. Of course, if you've already bought and paid for the game or dlc on steam or somewhere else, it's a non-starter probably.

            Brucehankins Suuuuper averse to Stadia, less because google per se and more because I'm not gonna pay money for something that may not exist in a few years (which, ofc, is because Google..), but that's irrelevant, the few things I can't get working on Solus aren't gonna be on Stadia lol XD Also, Geforce now > Stadia every day ;D Play what I already own, thanks!

            Most of the things I'm struggling with on Solus are small indie games/projects (like Deios by Dungeonfog, a map making software is a big one which finally convinced me to set up the Dual boot.. most of the RPG Maker games either worked well enough in a VM or I didn't care enough for the effort, but Deios was different), but I was able to get Win10 dual boot up and runnning anyhow ^.^

              tomscharbach (9) I remove the Windows drive from the computer. I put the other (soon-to-be Solus) drive into the computer. At this point, I again have only one drive in the computer.

              I understand everything in this great tutorial except this. Are you removing one drive by removing it from a bay and unplugging it from the board and putting the next drive in the same bay and same plugin on the board? Or different? Or would this (labeled board plugin slots) theoretically matter at all?
              Reason I ask: this tutorial makes me confident, and I've been running Solus alone for too many years, ergo companion OS has occurred to me lately

                  brent I understand everything in this great tutorial except this. Are you removing one drive by removing it from a bay and unplugging it from the board and putting the next drive in the same bay and same plugin on the board? Or different? Or would this (labeled board plugin slots) theoretically matter at all?

                  The computer I am using to dual boot is a Dell Optiplex 7000-series Micro. Micro-size computers are similar to laptops in configuration (limited drives, low-power CPU/GPU, and so on).

                  The Optiplex Micro has three drive slots -- two M2 drive slots (one for a 2280 "long" drive and the other for a 2230 "short" drive) and a 2.5" SATA slot with a snap-in plastic drive holder. So it is very simple to work with. I use the "long" M2 drive slot for an NVMe drive, and the 2.5" SATA slot for an SSD. I don't use the other M2 slot, so I effectively have two drives to work with. That makes the install process more or less idiot-proof, which is a good thing in my case.

                  I installed Windows on the M2 NVMe drive (back in the day when Linux support for NVMe was problematic) and Solus on the 2.5" SATA SSD drive. I popped out the 2.5" SATA drive when I installed Windows on the M2 NVMe drive, then popped it out. I put in the 2.5" SSD when I installed Solus on it, then, after Solus was installed on that drive, popped the M2 NVMe drive back into the M2 slot.

                  On a more typical desktop computer (e.g. a computer with an M2 slot or two and several SATA 2.5" SSD/HDD slots) the drive situation is more complicated, obviously.

                  I would follow the practice of setting up each of the OS drives in the bays/slots where the drive will reside at the end of the process -- that is, install Windows on the Windows-target drive in the bay/slot where it will reside permanently, and install Solus on the Solus-target drive in the bay/slot where it will reside permanently.

                  I would not set up both drives using the same bay/slot. I don't think that it would do any harm to use the same bay/slot to set up both OS's (modern motherboards seem to adjust to moving drives around**), but why do it? On a mid-size or full-size desktop computer, "removing" a 2.5" SATA SSD/HHD is as simple as unplugging the drive from the motherboard slot.

                  The three important principles are:
                  (1) Set up both installer USB drives (Windows and Solus) before doing anything else, and test them to make sure that they will boot before going further;
                  (2) Clean up the BIOS boot loader entries before installing (I don't know why, but BIOS seems to collect boot load entries, and when I install too many different OS's on my test computer, boot loader entries multiply like rabbits); and
                  (3) Unplug or remove all non-target drives when installing the OS on the target drive.

                  I'm going to mention Brucehankins so he can chime in if he has any thoughts on this issue. He has a lot more experience that I do, I suspect, and might have a better answer than I do.

                  ===========

                  ** I remember (correctly or not -- at my age you never know) that in the 1980's and even into the early 1990's some motherboards required the boot drive had to be in a specific slot (as I recall, the CD went into slot 0, the boot drive into slot 1, and additional drives went into slots 2 and up) but I don't think that is the case with modern motherboards.

                        brent So I don't know that I have more experience than tomscharbach but I do have at least 4 machines in the house that have 2 or more drives in them and a couple externals that I use as portable OS drives. The two machines I tinker with the most (Lenovo laptop and HP mini pc 300-020) only have a single SATA and single m.2 it makes it simple. The 2.5 SATA goes in that spot and the 2242 m.2 goes on the mobo. They always stay the same because there is no way to swap them. On the ATX tower PC's, I've got about 5 drive bays each. I don't think it matters where they go honestly, but I typically don't move them around. That's more out of ease/laziness than anything. The SATA connections are right in in the front when I remove the side panel, so all I have to do is pull the plug, never have to remove a drive from the bay. I do open up the mini pc and swap around the 2.5 SATA drive though with another of the two portables has openSUSE and Lubuntu on it. The portables were formally internal drives from older laptops that I salvaged out and bought some cheap external cases with SATA to USB for. I plug those in straight SATA when I want to install a new OS/Distro or get the idea I'm going to completely reformat it and have external storage only. I'm a big fan of the portable OS though, and it's come in handy more than one time to be able to just plug in via USB and have my own OS/data available with a machine restart.

                              tomscharbach I would follow the practice of setting up each of the OS drives in the bays/slots where the drive will reside at the end of the process -- that is, install Windows on the Windows-target drive in the bay/slot where it will reside permanently, and install Solus on the Solus-target drive in the bay/slot where it will reside permanently.

                              I would not set up both drives using the same bay/slot. I don't think that it would do any harm to use the same bay/slot to set up both OS's (modern motherboards seem to adjust to moving drives around**), but why do it? On a mid-size or full-size desktop computer, "removing" a 2.5" SATA SSD/HHD is as simple as unplugging the drive from the motherboard slot.

                              that's exactly what what I would do and I'm glad you would as well. Thank you for your thoughtful and thorough response, Tom.

                              Brucehankins hey always stay the same because there is no way to swap them. On the ATX tower PC's, I've got about 5 drive bays each. I don't think it matters where they go honestly, but I typically don't move them around.

                              Yeah! And that's two of the same mindset. I think it does matter and I would consider myself negligent by funneling the whole setup thru one board channel. Glad you are both superstitious/cautious about that point. Thanks Bruce

                                    brent Good luck to you Brent. Use your head when you set up dual boot and it will go fine. Let us know how it turns out.

                                    I thought of one more practical tip last night, it being Microsoft's "Patch Tuesday" so I had to update Windows. Before I run Patch Tuesday updates (those being about the only updates that require a restart, and sometimes more than one) I go into BIOS and set the Microsoft Boot Manager as the default before running the updates (so that Windows restarts run normally during the update process), and then switch the default back to the Linux Boot Manager after I am done.

                                        7 days later

                                        tomscharbach (2) Clean up the BIOS boot loader entries before installing (I don't know why, but BIOS seems to collect boot load entries, and when I install too many different OS's on my test computer, boot loader entries multiply like rabbits); and

                                        ok I have a W10 disk coming for the drive I nuked 2 years ago and I have no digital insurance outside of Solus since then. So I have all your 'individual drive' setup understood and I'm ready to act...
                                        except...how do I execute your number two? thanks

                                            tomscharbach Very nice write up. I am too lazy to pull out hard drives so in GParted I change the EFI partition flags to msftdata from Boot/ESP. In this way the new OS will not hijack the old EFI partition and it's a LOT less work.
                                            I have had Windows corrupt the other OS's EFI partition (on another drive) during an update before so now my default is leave them at msftdata until I need to change it to boot/ESP for an update. Then I change back after reboot.

                                              tomscharbach what you are talking about in step 2 is installing efi bootmanager from the SC, then manually removing dead entries, correct? And all but Solus, which I believe is also correct. My research is showing nothing else except use the EFI shell option (bios) to achieve the same thing but I don't know how to talk in that terminal.

                                                  brent I have a W10 disk coming for the drive I nuked 2 years ago and I have no digital insurance outside of Solus since then. So I have all your 'individual drive' setup understood and I'm ready to act...
                                                  except...how do I execute your number two? thanks

                                                  Yeah, the instructions ("(2) I create a USB installer for Windows using the Media Creation Tool (Windows 10 or Windows 11, as the case may be).") assume that you can set up a W10 installation USB using the Windows Media Creation Tool. Of course, you need Windows to do that, and you don't have Windows on the computer.

                                                  Two thoughts:

                                                  (A) Simplest: Ask a friend to bring over his/her/their Windows laptop, and set up the Windows installation USB using your friend's computer and your USB. The Windows 10 Media Creation Tool downloads a small (19KB) executable (MediaCreationTool21H2.exe), and does not make any permanent changes to the Windows computer on which it runs so long as you select the "Create installation media ..." option:

                                                  When the USB creation process is finished (it will take roughly 30 minutes to download Windows 10 onto the USB, check the file integrity, and make the USB bootable) you can remove the USB and use it to install Windows 10 on your computer.

                                                  This works flawlessly, and I do it all the time, using my primary Windows 11 computer to set up installation USB's to be used on other computers**.

                                                  (B) Not so simple, but will probably work from your Solus computer: Download the Windows 10 ISO using your Linux computer by using the Download Windows 10 link. Microsoft will eventually (and I do mean eventually, because it seems to take forever) redirect you to an ISO download page (the URL for that page is "https://www.microsoft.com/en-us/software-download/windows10ISO") that will allow you to download the ISO file to burn a bootable Windows installation USB.

                                                  The process of USB creation walks you through a series of simple steps, starting with selecting "Windows 10 (multi-edition ISO" (I think that it will be your only choice). After you click the blue "Confirm" button, follow the instructions, being careful to select the Windows 10 version (probably 64-bit Windows 10 Home, but possibly 64-bit Windows 10 Pro) that came with your computer.

                                                  After you've done that, the appropriate W10 ISO file will download (again, plan on about 30 minutes, depending on the speed of your network connection and the speed of your computer). The download is huge (5.5 GB) because it is downloading options for several Windows versions.

                                                  Once the ISO is downloaded you can create the installation USB using the bootable USB tool of your choice. ItsFOSS has a recent description of the process using Ventoy (scroll down to "Method 2: Create bootable Windows 10 USB using Ventoy") but I suspect that the method is more or less identical with the bootable USB creation tool of your choice. There are any number of articles/videos about different methods to create Windows 10 installation USBs, so feel free to read around and find one that appeals to you.

                                                  BOTTOM LINE

                                                  All of the Linux-based methods that I looked at seem unnecessarily complicated to my simple mind, so I strongly suggest that you beg/borrow/steal the use of a friend's Windows 10 or Windows 11 computer to set up an installation USB using the Windows Media Creation Tool.

                                                  ============

                                                  ** A Windows 10 installation USB can be created using either Windows 10 or Windows 11 (the result will identical -- the USB will install Windows 10) on the target computer. Just be careful to download the Windows 10 Media Creation Tool (MediaCreationTool21H2.exe) rather than the Windows 11 Media Creation Tool (MediaCreationToolW11.exe). If you use the "Download Windows 10" page, you'll get the Windows 10 WCT, but if you are mindless and use the "Download Windows 11" page, you won't.

                                                    brent tomscharbach what you are talking about in step 2 is installing efi bootmanager from the SC, then manually removing dead entries, correct? And all but Solus, which I believe is also correct. My research is showing nothing else except use the EFI shell option (bios) to achieve the same thing but I don't know how to talk in that terminal.

                                                    I'm getting lost. IF I understand what you are trying to do, you have Solus installed on your computer, and you want to install Windows 10 on a separate drive.

                                                    The reason I go into BIOS/UEFI (F2 on my Dell computers, maybe something else in yours) at several points in the process is to clean up the UEFI boot sequence before any installation. BIOS/UEFI gets cluttered over time -- for example, I remember seeing Windows Boot Manager, two instances of Linux Boot Manager, and several Grub entries on my test computer -- and the point is to clean it up, so that when you are done, you have Windows Boot Manager and Linux Boot Manager only as your primary boot managers.

                                                    You have Solus installed. Assuming that you don't have any other Linux distros installed, Linux Boot Manager should be the only UEFI boot option. If you have remnants (e.g. on or more Grub entries from former installations), I think that it is a good idea to get rid of them.

                                                    Why don't you go into your BIOS, and let me know what you see under "Boot Sequence" or whatever it is called in your BIOS.

                                                      @tomscharbach "IF I understand what you are trying to do, you have Solus installed on your computer, and you want to install Windows 10 on a separate drive."
                                                      Correct.
                                                      "is to clean up the UEFI boot sequence before any installation....and the point is to clean it up, so that when you are done, you have Windows Boot Manager and Linux Boot Manager only as your primary boot managers."
                                                      OK that's on me, I misinterpreted "clean/remove" these entries from posts of yours past as "clean/remove." What you mean is simply tidy boot order. That I can do. I have about 10 entries and as long as SolusPrimary and WinSecondary are 1 and 2, I'm good to go. I can't see a way to remove any boot order entries--only move them.
                                                      That's what I needed to know, thank you.

                                                      As for the spectacular post before that, thank you again. I have someone with W10 in the same room as me and have used her Media Creation Tool to burn the Microsoft-furnished ISOs...but none of the MS tools on those 2 isos (both 'recovery' iso and 'install iso) could fix humpty. Neither would the 'install' iso install; it questioned my validity. So I have another licensed avenue coming.

                                                      (for anybody reading our own woeusb software will burn WIN stuff in Linux ONLY if you NTFS format the usb).

                                                      Thank you so much for indulging me. I have never (like @WetGeek said in another post) wanted to dual boot, but with yor 'inividual' approach it just makes a wild amount of sense to me, especially in the confidence dept.
                                                      If we met in person I'd buy you a Jamesons on the rocks, splash of water, twist of lime, on ice. Take care and I appreciate your thoroughness with your dual boot method.