EDIT: I'm adding "(editX)" edits and "A: ..." answers to my question, to avoid posting it as an answer (for now)...
Similar to this question has been answered many times in forums and so on, but there are special requirements that I couldn't find in a single place.
Purpose - With the spy features of all paid OS, it become a need for many people to take more steps to keep their life as private as possible... A possible (and maybe only) long-time solution is to use Linux and (temporary) keep Windows for compatibility with special software (usually paid software, available for Win only)... In the future (after 3-5 years) a virtual machine may be used instead, but so far this multi-boot setup is required...
- multiboot system - multiple Win/Linux
- ability to install new Linux and Windows versions at any time (and restore the MBR after each Win installation?) - (!) installations are not in special order, but as the need arise!
- (optional) to be possible to encrypt chosen partitions (these with OS and/or data on them)
- to have at least one shared partition between Linux and Windows (read/write)
- (edit1) The computer uses BIOS, not UEFI (as presumed by Rod). This makes the task easier, according to what I read for UEFI. Probably UEFI users may use it too, by switching to CSM (Compatibility Support Module)...
- ...probably more ideas can come to my (your) mind, but these above seems the most important for the planning stage...
Here is what I have so far (you can directly copy and amend/change):
Planned partitions structure:
- hda1 (primary, ext4 512MB) - boot partition with Grub
I find appropriate to have a separate boot partition, where Grub to be installed (seems a requirement for the excryption option).
Q1: What type to choose - ext4? (Reference: this thread)
A1 (edit1): ext4 works just fine!
Q2: What size to choose? I found suggestions between 1 and 512MB...
A2 (edit1): I used size above 512MB, even 1GB+ (just to make sure is has enough space for backing up the whole contents of this partition - useful during the investigation/tests phase).
- hda2 (primary, NTFS 20-80GB) - Win 7, 8, 10 or newer
Q3: Win may need separate HDD for encryption? Some link(s) could be enough.
A3 (edit1): I left the encryption option as there are many pros and cons... It's not correctly to suggest to someone else without trying it first by youself for a few months or years...
- (optional) hda3 (primary) - Win 7, 8, 10 or newer
I'm planning to create this partition, just to have it ready if it's needed, but I'm not planning to use it... It could be used as data-sharing partition in the meanwhile...
Q4: Anything special for 2nd Windows to keep in mind?
A4 (edit1): I realised that when pre-partition the disk and prepare the partitions for Win, the Win setup doesn't create "hidden system boot partition" (it get's created if you re-partition the drive during the Win setup). Also I managed to manually create such "system boot partition" - for example by making /sda2 (or /sda1) "active/boot flag" and installing the Win on different partition /sda3 or even /sda7* (*logical drive also works for Win7). This way the Win boot manager also reside in it's own partition - which was prepared for encryption part... And something important, that could be very useful for some people: You can install Win boot loader on the same partition where the win is installed: for example - first, you set /sda2 to be "active/boot flag", then when you install Win it's boot record will be on /sda2 too! Second, make /sda3 "active/boot flag" and install another Win - it's boot loader will be installed in /sda3 too and there will be only one entry! If you don't set the /sda3 to be "active/boot flag", then the /sda2 boot loader will manage both installations and there will be 2 entries for Win, but it you want to format /sda2 and install another OS on it - you'll lose the boot record for /sda3 installation (I didn't tested this and I can't say if it's easy to recover it - probably that depends of the last Win OS boot loader that you install)!
- hda4 (primary) - Extended partition (contains all logical partitions)
- hda5 (NTFS, ?GB) - NTFS ('shared partition' between Win/Linux - read/write)
Q5: Is NTFS appropriate (and only) choice? (more choices discussed already)
A5 (edit1): Seems like NTFS is a good choice, probably FAT32 (not sure about exFAT) will work, but there are pros and cons... the most important is: FAT is limited to max 4GB file size!
- (optional) More shared partitions (ntfs) could be created if needed
- (optional) 'Non-shared partitions' (ext4) could be created too - for storing your data... and they could be encrypted as well?
Q6: If we need to encrypt these partitions, when and how to do this? Short answer with some link(s) should be enough.
A6 (edit1): Encryption part should be tested for at least few months before suggesting it to someone else, so I just dropped it off for now.
- hda6 (ext4, 10-60GB) - Linux1 root partition
Q7: What about encryption of the partition - when to be done and how? Short answer with some link(s) should be enough.
A7 (edit 1): Encription dropped off for now.
- hda7 (swap, 4-10GB *) - Linux1 swap partition
Consider the swap partition size based on your current RAM-size and real memory usage, and also consider hibernation (must have enough space to hibernate)!
- (optional) More linux distro's could be added (for testing and/or production to replace "Linux1"), so it's good to leave enough space on hda7 or later... (or as unallocated space) at end of the drive...
Now... I don't have enough practice and I'm not sure what are the steps to continue. I'm planning to make some tests in the next 5-10 days.
I'm sure there are going to be more questions, although I think whey would be answered already (as separated questions).
Installation steps I am planning so far (again - you can copy and amend the list):
- Re-partition the disk using Live CD
(edit1) Used Hyren's Boot CD and "parted magic" - deleted all old partitions and recreated according to the partitioning scheme above.
- Install Grub immediately?
(edit1) I tried a few Win installations first and tested setting the "boot flag" (make "active" under Win) to different primary partitions - /sda1, sda2 and sda3 - This way I managed to install independent copies of Win, so I can replace any of them when needed, without losing the boot loader for all Win-installations! (Note: WIn could also be installed on logical partitions, so probably you can have more than 3-4 installations, but the boot loader is always put on "primary and active /active=boot flag/ NTFS partition"...)
If I do this, then I'll have a case where I already have Grub installed and a new OS needs to be installed. That case is going to happen now or later - when Win 10.5 or Win 12 arrives... or when another Linux distro needs to be installed.
I find appropriate to start with it and when the time arrive - every person following the plan will have the needed skills to do what's necessary as he/she already did it at the initial setup.
(edit1) I followed Rod's advice and didn't start with Linux, but after installing Linux, I installed 4-5 times different Win versions for testing purposes and restored the MBR from a Live CD multiple times. A note: because of the "separate Grub partition", when reinstalling grub must be mounted the root partition and then the grub partition to ~~/boot, and then can be called grub-install.
- Install Linux1 to hda6 and hda7 (swap)
- Install Win7 to hda2
(these questions start from 31 intentionally)
Q31: Are there anything to keep in mind here? Something to set up before booting Windows installation from DVD? Specific Win 7,8,10 cases to consider?
A31 (edit1): Yes, there are things to be considered here!!! If you want to keep every Win independent of the other, it's best to manage the "active partition (boot flag)" to match the same partition where you are going to install Win, BEFORE you start the installation and boot from DVD/USB. This way you can just format the OLD Win partition and replace it with something else, without worrying about "how to restore Win boot loader" (I also don't know how to restore it!).
Restore MBR and add windows to Grub menu
...After some weeks/months of work using this multi-boot setup, we may need to add another OS for test and/or production...
Q32: Is there something special here, if we want to just replace a Win/Linux installation?
A32 (edit1): For Win - if setting the active partition before each installation, then there's no problem - every partition can be formatted and replaced with another Win as the WIn boot record will be placed on it's partition. Usually after installing Win, it's best to "reinstall grub2 to MBR using Live CD/USB"
If we add a new one, we may need to make another partition(s) - for another Linux distro... A note on "multiple Linux could use same swap partition" - if hibernate to disk is used, don't use single swap partition, otherwise you may lose the hybernated state and some data!!
Quite big plan and many things to consider... Please note I don't need very detailed plan (i.e. what command to execute), but "what to consider/achieve" at every step...!
I'll update my question to include specific links to each stage after I complete the test successfully. The aim is to create a plan, that many Win-users could follow and convert to Linux!