Les manufacturiers de disques durs considèrent que 1GB est égal à 1000MB. Windows reconnait 1GB comme étant 1024MB.

1k = 2^10 = 1,024
1M = 2^20 = 1,048,576
1G = 2^30 = 1,073,741,824

160,000,000,000 bytes (terme utilisé par les manufacturiers de disques durs)
160,000,000,000 / 1,024 = 156,290,904 kB
160,000,000,000 / 1,048,576 = 152,587.8906 MB
160,000,000,000 / 1,073,741,824 = 149.0116119 GB

Un disque dur de 160GB est donc reconnu à 149.01GB sous Windows.

Voici les calculs pour les autres tailles de disques durs :

"40 GB" hard drive = 40,000,000,000 bytes / 2^30 bytes in a gigabyte = 37.25 GB
"50 GB" hard drive = 50,000,000,000 bytes / 2^30 bytes in a gigabyte = 46.57 GB
"60 GB" hard drive = 60,000,000,000 bytes / 2^30 bytes in a gigabyte = 55.88 GB
"80 GB" hard drive = 80,000,000,000 bytes / 2^30 bytes in a gigabyte = 74.51 GB
"120 GB" hard drive = 120,000,000,000 bytes / 2^30 bytes in a gigabyte = 111.76 GB
"150 GB" hard drive = 150,000,000,000 bytes / 2^30 bytes in a gigabyte = 139.70 GB
"160 GB" hard drive = 160,000,000,000 bytes / 2^30 bytes in a gigabyte = 149.01 GB
"200 GB" hard drive = 200,000,000,000 bytes / 2^30 bytes in a gigabyte = 186.26 GB
"250 GB" hard drive = 250,000,000,000 bytes / 2^30 bytes in a gigabyte = 232.83 GB
"300 GB" hard drive = 300,000,000,000 bytes / 2^30 bytes in a gigabyte = 279.40 GB
"320 GB" hard drive = 320,000,000,000 bytes / 2^30 bytes in a gigabyte = 298.02 GB
"400 GB" hard drive = 400,000,000,000 bytes / 2^30 bytes in a gigabyte = 372.53 GB
"500 GB" hard drive = 500,000,000,000 bytes / 2^30 bytes in a gigabyte = 465.66 GB
"750 GB" hard drive = 750,000,000,000 bytes / 2^30 bytes in a gigabyte = 698.49 GB
"1 TB" hard drive = 1,000,000,000,000 bytes / 2^30 bytes in a gigabyte = 931.32 GB