Does partition software generally make 100% sure it is only partitioning away free space ?Generally
yes, however that shouldn't stop you from checking at least twice exactly what is going to happen once you click the GO button.
Does the software move files away from the end of one partition to create the next partition before
doing anything else ?
No. By this question I'm assuming you're talking about creating a new partition on a drive that's already in use. You should resize existing partitions to create the free space you require for the new partition. Only the Resize/Move functions of partitioning software will move files, anything else will generally destroy.
Should you defragment before partitioning ? (presumably it is a smart idea). In any special way ?
For a drive with existing partitions that you want to keep, yes. For a drive in which you intend to delete all or some partitions to create free space for new partition(s), no.
ie. If you intend to use Resize/Move to create enough space for a new partition, then you might
gain a little speed by defragging first. However, when you factor in the time for defragging + partition resizing/moving against just a straight resize/move - is there a net gain?
This will depend on whether you do your partition butchering with the OS online or offline.
Offline - you have the benefit of the OS not interfering with your operations but may lose the benefit of better interface drivers, (hence speed).
Online - you have the benefit of possibly better interface drivers but the OS might require you to restart to complete the operations anyway.
Generally, I do all partition operations offline.
Does this question vary a lot between software products ?
Depends on driver support generally but otherwise, no.
Do you find any great functional fundamental distinction between the Windows products (Paragon, Easeus, Aomei, etc.)
and the more tech partition stuff like Terabyte (Bootit) that works outside Windows ?
No, since they almost
always provide a version that lets you do it all with the OS offline. eg. Paragon has a bootable Linux version for both their free/pay versions - pay versions also get a WinPE based version which has better driver support.
In the old days it made a difference where you started partitioning (e.g. in XP or underneath). Is that a factor today ?
I haven't found it to be.
Granted there are functional differences in products, (e.g. a Pro product compared to Lite or Free will show you
some differences, as will reviews) and there are differences in support and cost. It seems like the software has
generally become fairly good. One feature I noticed is that some software may be stronger than others in simply
moving x gigabytes of space from one partition to another.
Your thoughts ?
Before I partition anything to do with the drive the OS is on, I will make an offline image of the OS partition, (or the whole drive if the partition occupies the whole drive - <40GB in total), to an external drive - in my case I just boot into Paragon HDM11Pro on an external and do everything from there, (backup/partitioning).
For any other drive, (ie. data drives), I'll just make sure that any data I don't want to lose is backed up - which isn't much compared to the size of the drives, (~200GB out of a total of ~4TB). A Microserver takes care of OS and essential data backup, (monthly, weekly and daily), and I also have a 640GB USB3 drive that triggers a data backup when it's plugged in.
Anything else, I'm prepared to wear the loss, (eg. Steam games, downloads, etc), because I just look at it as I probably needed to clean the drive out anyway - even the OS falls under that category, it's not essential to back it up, just convenient.
These days the quality of software amongst the various big names, (Acronis, Paragon, EASUS, etc), are reasonably equivalent - the only major difference I've found is in the drivers they provide, (for offline), since these will determine the speed at which operations will get done.
My short-term attempt is to take my lightly used Windows 7 64-bit puter and add a d: and some drives for
a linux install. And I may do similar on a spare older XP system.
My recommendation from the times I've dabbled with a Linux install is to create all the partitions first, ie. root, user and swap. When it comes to installing, the Linux installer will find those partitions and automatically use them instead of throwing you into the installers partitioning tool.