Picture the
scene, you have just bought a new 1TB hard drive, installed it into your
computer, fired it up, formatted it and see that it’s only 0.9TB in size. What
happened to the rest? Have you lost data or is the hard drive broken?
This is a common question we hear at Dave’s Computers in New Jersey. Very common in fact. Whenever we install new hard drives for customers and fire up their computer to show them, 9 times out of 10 we are asked why it’s smaller than what we said we installed.
The hard
drive is exactly the size we said it was but the way the operating system
reports it is different. You’ll have to bear with me as there is some math
involved.
If you buy
a 1TB hard drive, it will have the capacity to store 1TB of data. However, once
formatted in Windows it will show much less.
1TB, or
terabyte equals 1,000,000,000,000 bytes. That’s a trillion bytes. It will have
somewhere in the region of 1,953,525,168 sectors of 512 bytes each. With the
help of my trusty calculator, that gives us 1,000,204,886,016 bytes of storage.
Slightly above the advertised capacity.
When you
format it in Windows, you won’t get those numbers. The reason is that round
numbers work fine in hardware but don’t work in software. A number has to be
equally divisible in software programming to make it work. So where 1TB is a
nice round number to hard drive manufacturers, it isn’t divisible by that 512
byte size.
Windows
will instead measure the drive in multiples of 1024 or 512 which will result in
a different size. Then you have to add the format data to that.
Think of a
file system like a library. The building itself could be large but once you put
the bookshelves in, the building looks a lot smaller. The same principle
applies to a hard drive. Once Windows loads its file system, the available
space is reduced. Then add Windows Shadow File System which is like a secure
copy of files and even more space has gone.
So you
haven’t lost any data and you haven’t been robbed. It’s just the differences in
how hardware manufacturers and Apple and Microsoft calculate size. Then add the
file system and essential data to come up with available space.
If you want
to try it yourself, open a CMD window in Windows. Select your new hard drive by
typing ‘D:’ or whatever and hit Enter. Type ‘vssadmin list shadowstorage’ and
hit Enter.
You will
see Shadow Copy Storage space of 5-10GB. This is some of the shortfall in space
and why Windows says your disk is smaller than it actually is.