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Why is the capacity of my storage device (as reported by operating systems - O/S) different than the capacity that is listed on the device label?
All devices and operating systems – O/S (MAC, Windows, Android, etc.) reserve a certain amount of space when initially mounting any kind of storage media (flash, hard drives) to ensure that there is enough room on the formatted media for error bit/sector swap out and other system housekeeping tasks associated with proper media management tasks. While the manufactured, i.e. unformatted capacity, may for example be 16MB, the formatted capacity is always something less than that amount for the above reasons. Additionally, each O/S has their own internal algorithm measuring these capacities and when considered in the context with device drivers, chipsets and firmware variables, can report different formatted capacities across different brands of storage media including hard drives.

While well known to the power user, a regular end user without previous experience, may mount a flash storage card in their camera or tablet or on their computer and wonder why the listed storage capacity isn’t being read back ‘correctly’ after mounting on their device. There isn’t any “lost” capacity going on; just space utilized in a manner that provides for proper data and device integrity within the original overall rating capacity, now showing the final capacity that is accessible for user access.

The process of figuring out calculated amounts is shown in the following information. Remember, standardization of parts and industry storage capacities start right at the beginning of the entire manufacturing supply chain process when large industrial DRAM chips providers are supplying those raw material parts to construct the final storage device you purchase as an end user. Also, you won’t see a storage capacity that is reduced by some crazy number like 50% - such a situation might indicate some error issue requiring further investigation. Also, depending on the format type selected – 32/64bit- FAT32/NTFS to name a few common ones – considering the default sector size – 8/16/32bit – used by the O/S, final capacity has a range of acceptable size variances, some less, some more than other O/S or devices but once understood at a formatted device level, the end user should have confidence that the storage media integrity and accessible capacities are proper and in line with the above technical considerations.

Operating Systems commonly define capacity as follows:
  • Kilobyte (KB) as: 2 to the 10th power (1,024 bytes)
  • Megabyte (MB) as: 2 to the 20th power (1,024 X 1,024 bytes = 1,048,576 bytes)
  • Gigabyte (GB) as: 2 to the 30th power (1,024 X 1,024 X 1,024 bytes = 1,073,741,824 bytes)
Wintec Industries uses industry standard definitions to define storage capacity as follows:
  • Kilobyte (KB) as: 1 thousand bytes (exactly 1,000 bytes)
  • Megabyte (MB) as: 1 million bytes (exactly 1,000,000 bytes)
  • Gigabyte (GB) as: 1 billion bytes (exactly 1,000,000,000 bytes)
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