a screenshot of a disk disk with the disk disk properties highlighted

Why you can’t use 100% of hard drive capacity

If you look closely you’ll see that hard drives never show their full advertised capacity.

Perhaps you’ve bought a nice new 1 TB hard drive to copy files to – but it only shows 930 GB of available space.

But why can’t you save 1 TB of files on that new 1 TB hard drive and where has the missing space gone?

There’s typically three answers to this question.

1. Hidden partitions

If the drive has Windows installed on it, there’s a hidden system partition of 100 MB – this space is used to store boot information for Windows when it loads.

Additionally, if the computer came from a manufacture such as Lenovo or Dell it may have a recovery partition around 10 GB in size. This partition is used if you ever need to restore the computer to how it come from the factory.

2. Bytes – 1024 vs 1000

Hard drive manufactures count the storage in bytes, and count 1000 bytes in a kilobyte.

However Windows operating system counts 1024 bytes in a kilobyte.

The 24 byte difference makes a 1 TB hard drive appear as 931.32 GB of usable space to the operating system.

3. Sector size

Hard drives use sectors to store information.

Each sector is typically 4 KB – but two blocks of information cannot share the same sector.

Meaning a 300 byte file will take up the full 4 KB of space – leaving the rest unusable.

This causes discrepancies between the data you see and the actual space it occupies on the hard drive.