This answer explains why a hard drive may display a different (smaller) capacity than the indicated on the drive label.*END
Determining drive capacity can be confusing at times because of the different measurement standards that are often used. When dealing with Windows and Mac based systems, you will commonly see both decimal measurements and binary measurements of a drive's capacity. In either case, a drive's capacity is measured by using the total number of bytes available on the drive. As long as the drive displays the correct number of bytes (approximate), you are getting the drive's full capacity.
Note: |
Apple published an article titled, "How Mac OS X reports drive capacity" detailing how it reads drive sizes. This article includes some changes made in Mac OS X v10.6 Snow Leopard (this also applies to 10.7.x (Lion)) in how the OS reports drive sizes.
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Decimal vs. Binary:
For simplicity and consistency, hard drive manufacturers define a megabyte as 1,000,000 bytes, a gigabyte as 1,000,000,000 bytes and a terabyte as 1,000,000,000,000 bytes. This is a decimal (base 10) measurement and is the industry standard. However, certain system BIOSs, FDISK and Windows define a megabyte as 1,048,576 bytes, a gigabyte as 1,073,741,824 bytes and a terabyte as 1,099,511,627,776 bytes. Older Mac systems also use these values. These are binary (base 2) measurements.
To Determine Decimal Capacity:
A decimal capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,000,000,000 using base 10).
To Determine Binary Capacity:
A binary capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,073,741,824 using base 2).
This is why different utilities will report different capacities for the same drive. The number of bytes is the same, but a different number of bytes is used to make a megabyte, a gigabyte and a terabyte. This is similar to the difference between 0 degrees Celsius and 32 degrees Fahrenheit. It is the same temperature, but will be reported differently depending on the scale you are using.
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Important:
If you are dealing with drive sizes smaller than the Approximate Binary Capacity of your Drive Size, then you may be dealing with either a BIOS limitation, or a Windows drive size limitation. For more information, please see the link below.
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Various Drive Sizes and their Binary and Decimal Capacities
| Drive Size |
Approximate Total Bytes |
Decimal Capacity
(bytes/1,000,000,000)
(Usual Displayed Capacity On Mac OSX)
|
Approximate Binary Capacity (bytes/1,073,724,841)
(Usual Displayed Capacity On Windows and Linux) |
| 10 GB |
10,000,000,000 |
10 GB |
9.31 GB |
| 20 GB |
20,000,000,000 |
20 GB |
18.63 GB |
| 30 GB |
30,000,000,000 |
30 GB |
27.94 GB |
| 36 GB |
36,000,000,000 |
36 GB |
33.53 GB |
| 40 GB |
40,000,000,000 |
40 GB |
37.25 GB |
| 60 GB |
60,000,000,000 |
60 GB |
55.88 GB |
| 74 GB |
74,000,000,000 |
74 GB |
68.91 GB |
| 80 GB |
80,000,000,000 |
80 GB |
74.51 GB |
| 100 GB |
100,000,000,000 |
100 GB |
93.13 GB |
| 120 GB |
120,000,000,000 |
120 GB |
111.76 GB |
| 150 GB |
150,000,000,000 |
150 GB |
139.69 GB |
| 160 GB |
160,000,000,000 |
160 GB |
149.01 GB |
| 180 GB |
180,000,000,000 |
180 GB |
167.64 GB |
| 200 GB |
200,000,000,000 |
200 GB |
186.26 GB |
| 250 GB |
250,000,000,000 |
250 GB |
232.83 GB |
| 300 GB |
300,000,000,000 |
300 GB |
279.40 GB |
| 320 GB |
320,000,000,000 |
320 GB |
298.02 GB |
| 400 GB |
400,000,000,000 |
400 GB |
372.52 GB |
| 500 GB |
500,000,000,000 |
500 GB |
465.65 GB |
| 640 GB |
640,000,000,000 |
640 GB |
595.84 GB |
| 750 GB |
750,000,000,000 |
750 GB |
698.47 GB |
| 1 TB (1000 GB) |
1,000,000,000,000 |
1 TB (1000 GB) |
931.30 GB |
| 1.5 TB (1500 GB) |
1,500,000,000,000 |
1.5 TB (1500 GB) |
1396.95 GB |
| 2 TB (2000 GB) |
2,000,000,000,000 |
2 TB (2000 GB) |
1862.6 GB |
| 3 TB (3000 GB) |
3,000,000,000,000 |
3 TB (3000 GB) |
2793.97 GB |
| 4 TB (4000 GB) |
4,000,000,000,000 |
4 TB (4000 GB) |
3725.29 GB |
| 5 TB (5000 GB) |
5,000,000,000,000 |
5 TB (5000 GB) |
4657.49 GB |
| 6 TB (6000 GB) |
6,000,000,000,000 |
6 TB (6000 GB) |
5587.94 GB |
| 7 TB (7000 GB) |
7,000,000,000,000 |
7 TB (7000 GB) |
6519.36 GB |
| 8 TB (8000 GB) |
8,000,000,000,000 |
8 TB (8000 GB) |
7450.58 GB |
| 10 TB (10000 GB) |
10,000,000,000,000 |
10 TB (10000 GB) |
9613.37 GB |
| 12 TB (12000 GB) |
12,000,000,000,000 |
12 TB (12000 GB) |
11176.04 GB |
| 14 TB (14000 GB) |
14,000,000,000,000 |
14 TB (14000 GB) |
13038.72 GB |
| 16 TB (16000 GB) |
16,000,000,000,000 |
16 TB (16000 GB) |
14901.39 GB |
| 20 TB (20000 GB) |
20,000,000,000,000 |
20 TB (20000 GB) |
18626.74 GB |
| 24 TB (24000 GB) |
24,000,000,000,000 |
24 TB (24000 GB) |
22352.09 GB |
| 28 TB (28000 GB) |
28,000,000,000,000 |
28 TB (28000 GB) |
26077.44 GB |
| 32 TB (32000 GB) |
32,000,000,000,000 |
32 TB (32000 GB) |
29802.79 GB |
| 40 TB (40000 GB) |
40,000,000,000,000 |
40 TB (40000 GB) |
37253.49 GB |
| 50 TB (50000 GB) |
50,000,000,000,000 |
50 TB (50000 GB) |
46566.86 GB |
| 75 TB (75000 GB) |
75,000,000,000,000 |
75 TB (75000 GB) |
69850.29 GB |
| 100 TB (100000 GB) |
100,000,000,000,000 |
100 TB (100000 GB) |
93133.73 GB |
In case the answer did not answer your question, you can always visit the WD Community for help from WD users.
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