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Why actual capacity of some USB flash drives is smaller than the nominal capacity

Answer: This is mainly due to the different methods of converting storage capacity.

There are two ways to convert storage capacity, one is decimal conversion method and the other is binary conversion method. 1GB=1000MB when using decimal conversion method; 1GB=1024MB when using binary conversion method.

When using the decimal conversion method, 1GB = 1000MB; when using the binary conversion method, 1GB = 1024MB. usually, some storage product manufacturers in order to calculate the convenience of the decimal conversion method, and in the computer computer, the system uses the binary conversion, so that the USB flash drive in the computer computer system calculations to identify the actual capacity of the numerical value less than the USB flash drive manufacturer's nominal capacity. Interested can go to the calculation, here to 128G as an example of the calculation, the calculation exercise is as follows.

As the smallest unit of storage for the byte (Byte), in the manufacturer's conversion for 1KB = 1000Bytes, 1MB = 1000KB, 1GB = 1000MB.

Therefore, the capacity of 128G to the manufacturer is so calculated:

128G=128*1000*1000*1000 (Bytes).

For the computer computer system, 1KB = 1024Bytes, 1MB = 1024KB, 1GB = 1024MB, so in the computer computer, by the system conversion: 128 * 1000 * 1000 * 1000 * 1000/1024/1024/1024 = 119.2093G.

Obviously, the computer computer system shows the actual use of the U disk capacity than storage manufacturers in the storage products on the standard nominal capacity is less.

The above is still the theoretical value, in fact, the U disk itself there will be some flash drive inherent file system occupies storage space, such as the FAT file system, which includes the MBR master boot partition, FAT file allocation table and ROOT directory area. But this occupied storage space is relatively small, usually just a few dozen, a few hundred KB.

In addition, there is the FLASH flash chip particles may have a certain amount of bad blocks (Bad Block), as long as these bad blocks within a reasonable range, the USB flash drive is still a qualified product. Bad blocks can not be used, will be master control "ignore" or "cover", will not be counted into the storage capacity.

Due to the above reasons, the actual capacity value measured by computer equipment may be slightly lower than the theoretical conversion value.

There is a relatively default "industry standard" is that as long as the actual capacity of the USB flash drive identified in the computer system is not less than 93% of the storage manufacturer's nominal capacity, is reasonable, and relax a little to reach 90% or more is also qualified. If the actual capacity of the purchased USB flash drive is too much lower than this percentage, then buy the USB flash drive may be a false label of the USB flash drive products, pay attention to identify.