Max wrote:

About a year ago I had to re-install Windows to get over a virus, and
even though it was overwriting the old o/s (the set-up process
confirmed this, as it gave me a warning), I noticed later it had not
built the registry from scratch.

An in-place upgrade (Repair) is NOT the same as a fresh install. A
fresh install has you wipe the partition (format it) before installing
the OS. You never said that you formatted the partition when you did
the reinstall. Looks like you did a Repair instead of a fresh install.

Anyway..... one year on, and I'm again re-installing Windows, but on a
different PC. This time I completely removed and created a new (the
only) partition. Did the install business, yet once again, I happened
to find an entry which again proved it's not starting completely from
scratch!

Deleting a partition and recreating it with the same exact endpoints
(sector offsets) means you still having everything that was in that
partition. This is how partition recovery works if, for example, you
accidentally deleted a partition and then need it back. The partition
table merely says WHERE is the partition, not what is inside of it.
Deleting partitions doesn't touch any of the sectors inside that
partition. Creating a partition doesn't touch any sectors inside those
endpoints. After all, just how long does it take to delete or create a
partition? Milliseconds after you click the Okay button. Obviously the
procedure didn't touch anything in the partition.

You have to *FORMAT* a partition if you want to remove its contents. So
did you do format before you installed the OS? Did you opt to format
the partition during the install of the OS?