I would say Windows is reporting it correctly, the Manufacturers have
changed the way of SELLING hard drive space.
Both are inaccurate.
The drive-makers tend to over-list a drive ... but not nearly as badly
as they used-to. "Back when", companies would list a drive's RAW
byte-count, before formatting. IOW, the number of bits the controller
could write from index-to-index divided by eight.
This practice stopped (and was already dying) when they went to SCSI and
ATA drives with internal formatting, where the user *couldn't* write a
whole track as a single block.
However drive-makers even then tended to call all of the extra (but
hidden) sectors on a drive that are used to reallocate defects as part
of their advertised "size".
They *still*, even now, tend to use decimal byte-counts (which look
bigger) than megabyte-counts (1024 bytes = 1Kb, 1,048,576 bytes = 1Mb,
1,073,741,824 bytes = 1Gb) to count how big a drive they're selling.
Those (of course) are RAW bytes available to the OS to use (supposedly).
To actually *use* a drive however, doesn't leave *nearly* that many for
the user.
1. Every drive has to have a "boot sector" set aside and written
(actually, far more than just a single sector, these days) it must also
be "partitioned" a "formatted.
2. When partitioned, some of the space is lost defining the partition.
Also, far more space is lost in various formats that don't allow
partitioning the full space available; so there's some unpartitioned
space left over in almost every drive these days. The bigger the drive,
the more likely. In my 160-gig drive (for example), even when I tell
Windows to partition the entire drive as one huge volume, 8 gig is left
over. ;-{
It seems a bit of a waste to not use 8 gigabytes; but far more to waste
a drive-letter for something that small these days. (Eight *gigs* is
small?)
3. Finally, in "formatting" a drive, space is needed on the drive for
the operating system to tell where things are stored. Spaces for
directories, "FAT tables" or the equivalent, and other information.
Even if (like in some OS schemes) they just start with a basic simple
directory-structure that can be expanded; with directories just being
another type of file, and locations stored similarly, when you end up
with much of the disk space used, the directory structure still takes up
considerable space that cannot be used by other files.
Windows doesn't count all those as space on the disk when it reports a
drive's "size".
So: Who is wrong?
Neither, both.
Depends on your viewpoint.
You just have to keep it in mind when buying a drive that a certain
percentage of the drive's "sale size" won't be left as "user size".