Disk overhead is the reason why a computer hard drive or storage device's capacity may show its capacity as different from its actual capacity.
For example, a computer company sells a
hard drivethat is marked as 200 gigabytes. When connected to a computer, it is shown that the actual storage capacity is 181.9 GiB (for example).
One common reason is that the computer company or hardware manufacturer reflects the size of the hard drive either in the standard system (where 1 KB = 1000 bytes) or the Binary-prefix system (where 1 KB = 1024 bytes). To avoid confusion, the Binary prefix symbols were renamed KiB, MiB and GiB with the advent of the IEC system. In this context, one KiB equals 1024
bytes. However, which convention the manufacturers or operating systemuse usually depends on them.
*1 KB = 1,000 bytes = 0.98 KiB
*1 MB = 1,000,000 bytes = 0.95 MiB
*1 GB = 1,000,000,000 bytes = 0.93 GiB
*1 TB = 1,000,000,000,000 bytes = 0.91 TiB
Finally, some space inside a hard drive can also be used by the
file systemfor its internal use (ex: FAT table) (usually less than 1% on drives larger than 100 MB), or for data integrity and fault-tolerance (like RAID) (i.e. in a RAID1 you will lose 1/2 of your space to mirroring, and in a RAID5 with "x" drives you will lose 1/"x" of your space to parity). The latter is only seen in devices that contain multiple drives but are marketed as a single drive (i.e. NAS devices and external HDDs).
Binary prefix(KiB, MiB, GiB, etc.)
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