Thank you Adam, you are correct. I have 249,997,291,520 bytes shown (which
is pretty darn close to the advertised 250 GB, but right beside it reads 232
GB.
-- I could swear it used to read 236 GB but that's a mystery for another day.
Why would Microsoft understate something?
It for sure can be a little confusing. You'll typically see slight
differences between different brands of hard drives and even between
identical models of the same drive. Aside from the marketing slight of
hand the formula is 1,024 bytes in every kilobyte. This has been the
standard since 1970. To keep the math simpler it is often rounded down
to 1,000, so if you have a 50K file you know that's roughly 50,000
bytes while in fact it actually is 51,200 bytes. As long as we're
playing number games, a lot of people may not know that a byte is
further divided into 8 bits.
http://computer.howstuffworks.com/bytes.htm
Go to at least the second page of above article to get to the meat of
what's explained and how computers use the binary system to do ALL
they do.
Also keep in mind the size of the hard drive and how many platters it
has determines it's capacity. But wait... that's is it's raw
potential. To use the hard drive it needs to be formatted. Part of the
pre formatting process is to detect and prevent any bad sectors on the
hard drive from getting written to in order to protect the data that
will ultimately get written to it. This is the HARD formatting the
drive has already undergone before you touch the drive.
All drives regardless of brand right out of the box have some bad
sectors. They use to list how many bad sectors on the drive's label.
They don't typically do that anymore. That's just the nature of the
beast. That of course reduces the disc's capacity by a small degree
depending on how many bad sectors there are to begin with. If the
operating system or the drive's own logic detects some sectors have
gone bad once you start using it these sectors also become
unavailable. So over time, yes, how much your drive can hold can
shrink and this can be a warning sign the drive is starting to fail.
Finally installing the file handling system like NTFS eats up some
space as overhead. So if I remember correctly what Windows is
reporting when you look at it's total capacity in Explorer is how much
it can hold after bad sectors are factored in and after the file
system has been installed so it's a net, not gross figure that can
vary slightly drive to drive even if they are the same capacity.
That isn't the end of the story.
The way Windows is designed it can't write data to a hard drive that
only fills up part of a sector. It MUST fill out the sector. The
difference between a file's actual size (it's byte count or what's
really data) and what is left as free unfilled space in the sector is
called file slack. Click on any file's properties in Explorer and
you'll see two numbers. Size and size on disk.
For example I just clicked on a jpeg file. Windows reports it is
91,914 bytes, but is taking up 94,208 bytes on the disk. The
difference of 2,294 is file slack and can be bits of any file or
memory page that Windows just grabs at random to fill the sector out
every time you write data to the disk.
When you first format (soft format) a hard drive you can change the
size of sectors to reduce waste caused by file slack. You can make
sectors larger or smaller depending on the size of your typical files.
With today's large capacity drives generally not worth messing with
just bringing it up to illustrate a lot of the space taken up on your
hard drive is wasted and is just file slack. Just how it is. A typical
hard drive has up to 20% file slack. Another reason to defrag once in
awhile which will often recover some of the wasted space in addition
to resolving files being scattered in pieces all over your drive.
