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Flash Memory Total Capacity
Reference Number: AA-00219 Views: 5696 Last Updated: 2014-11-26 10:09

When a flash drive or flash card is viewed with Windows Explorer, the capacity is less than the advertised capacity. For example, an 8GB flash drive may show 7.44GB when formatted with no data on the device.

This condition is normal and may apply to USB flash drives or flash cards.  Due to overhead and management of flash products, the available capacity may be less than the rounded total capacity.  This is generally true of all manufacturer's flash products.  All TDK Life On Record flash drives have a statement on the packaging to this effect:
 "*1GB = 1,000,000,000 bytes.  Actual capacity may vary.  Some capacity is used for memory maintenance and other functions and is not available for storage."


Users should also be aware that this definition is the Base 10 definition.  Microsoft and other operating systems use the Base 2 representation where 1GB = 10243 = 1,073,741,824 bytes.  Since Microsoft uses this format, capacities displayed in Windows Explorer, for example, will show what appears to be a lower capacity.  Dividing the full capacity by the above number should approximate the value displayed by Windows.
 There are various on-line discussions of this difference in defining GB that may be helpful.
 Also, flash memory, analogous to hard drives, allocates some capacity to use for reassignment of locations that may become unusable during the lifetime of the product.  In addition, some of the capacity is used for overhead and operation of the drive.  This is particularly true of the USB encrypted flash drives such as the Secure Plus.  These units use a small portion of the total capacity of the drive for the read only partition that is used for the control software and other security functions.

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