Why can’t I use 100% of hard drive – where has it gone?

You’ve no doubt noticed that you can’t use 100% of the space on a hard drive. 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.

Hidden partitions

If it’s a drive that 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’ll likely 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.

Bytes – 1024 vs 1000

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

Sector size

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

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