I'd love to be able to say that you and grelber are on the mark, but, sorry, nope; you're correct as respects drives in general, but not as respects my specific current circumstances.
First, and as I mentioned in my OP, close to 100% of those missing 350 MB were recognized when I initially partitioned the drive.
And second, here's a comparison of my four storage devices:
1. Internal Toshiba: Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 500.11 GB Â Â Â Â Â Â Â Total capacity
                                                499.37            Capacity of 4 partitions
                                                  0.74              Overhead =
0.15%2. External WD Scorpion Blue:Â Â Â Â Â 500.11 GBÂ Â Â Â Â Â Â Â Â Total capacity
                                                 499.77              Capacity of 2 partitions
                                                     0.34             Overhead =
0.07%3. Sony thumb drive:       1,002,438,656 Bytes     Total capacity
                                      1,002,397,696            Capacity of 1 partition (
Exact same for 2)
                                                 40,960             Overhead =
0.004%4. Patriot Xporter XT thumb drive: Â 8.02 GBÂ Â Â Â Â Â Â Â Â Total capacity (*)
                                                    7.54              Capacity of 2 partitions (7.67 last night)
                                                    0.48              Overhead =
6.0%(*) During the partitioning process, DU showed that 8.02 GB was available but delivered 7.67 for 1 partition, 7.54 for 2, and 7.41 for 3 (at which point I quit trying).
The Patriot's overhead % is clearly disproportionate, and it could not have supported its high price, would not have garnered its excellent reviews, if that % were default. (
Edit: It would never have been marketed if its default overhead % was 6%.)
I'm afraid my expensive drive has morphed into expensive trash…not even a paperweight…too light.
(The drive is 4 years 3 months old, but I've got no idea what "
normal" life expectancies are.)