Description of actual capacity of memory card

Welcome to use our brand of memory cards. First of all, we are very grateful for your choice and trust! Please be informed that the actual available capacity of all storage products (including memory cards, USB flash drives, mobile hard disks, etc.) will be smaller than the nominal capacity marked on the product surface. This is not a product quality issue, but rather caused by various normal factors such as industry common standards, technical specifications, and product design. The following is a detailed explanation of the relevant situation for your better use of this product.

1. Core reasons for the discrepancy between actual capacity and nominal capacity

There are two main reasons why the actual available capacity of a memory card is smaller than its nominal capacity. Both reasons comply with industry standards and are considered normal phenomena. The specific reasons are as follows:

(1) Differences in capacity calculation standards (the primary reason)

When marking the nominal capacity, memory card manufacturers adopt the internationally recognized decimal calculation standard, which states that 1GB equals 1000MB, 1MB equals 1000KB, and 1KB equals 1000 bytes. This standard facilitates production measurement for manufacturers and intuitive understanding for users, and is also a common marking specification in the storage industry. However, when you view the capacity of a memory card on devices such as computers and mobile phones, the device system adopts the binary calculation standard, which states that 1GB equals 1024MB, 1MB equals 1024KB, and 1KB equals 1024 bytes. This is because the underlying operations of computer systems rely on binary data, and thus require this standard to identify storage capacity.

The discrepancy between the two calculation standards directly leads to deviations in capacity display. The larger the nominal capacity, the slightly increased the deviation value, but the deviation ratio remains basically constant. For example, a memory card with a nominal capacity of 1TB, when calculated in decimal, is 1000×1000×1000×1000 bytes, which is approximately 931GB when converted to binary. This is basically consistent with the actual capacity displayed by the device. A memory card with a nominal capacity of 64GB, when converted, has an actual usable capacity of approximately 57.6GB, both of which fall within the normal range.

(II) System occupation and reserved space

Before leaving the factory, memory cards are pre-configured with necessary system files and functional partitions to ensure their normal operation, including file allocation tables, boot partitions, bad block reserves, etc. These contents occupy a portion of the capacity and are not displayed in the "available capacity" of the device.

1. System file occupation: Memory cards require a specific file system (such as FAT32, exFAT, etc., with different file systems corresponding to memory cards of different capacities, in accordance with the specifications of the SD Association) to store and read data. The file system itself occupies a small amount of capacity, used to record information such as file location and storage status;

2. Bad block reserve area: During the production process of flash memory chips, there may be a very small number of "bad blocks" that cannot be used normally. To ensure product stability and data security, manufacturers reserve a portion of space for replacing bad blocks. This space is not available for external use and is not included in the actual usable capacity;

3. Function reservation space: Some memory cards reserve a small amount of space to support additional functions such as firmware updates and encryption protection, ensuring long-term stable use of the product.

II. Reference Table for Common Nominal Capacity and Actual Usable Capacity

The following is a reference range for the actual usable capacity of memory cards with different nominal capacities (due to differences in product models and file systems, there may be a ±2% deviation, which is normal). Unit: GB

Nominal capacity

Reference range of actual available capacity

16GB

14.8-15.2GB

32GB

29.5-30.5GB

64GB

57.0-58.2GB

128GB

100-116.0GB

256GB

210-231.0GB

512GB

420-462.0GB

1TB

915.0-925.0GB

2TB

1830.0-1845.0GB

III. Important Notes

1. The deviation in actual available capacity is a normal phenomenon in the industry, which complies with relevant standards of the International Electrotechnical Commission (IEC) and specifications of the SD Association. It does not affect the normal use, read and write speed, or data security of the memory card, and is not a product quality issue;

2. The system calculation methods of different devices (computers, mobile phones, cameras, etc.) are consistent, all adopting the binary standard. Therefore, the actual capacity viewed on different devices is basically the same. If there are minor differences, they are mostly caused by the device system cache occupation, which is not a cause for concern;

4. We recommend that you format the memory card (by selecting the corresponding file system) using a legitimate device before use. After formatting, the capacity will be further stabilized within the reference range, and at the same time, it will avoid abnormal capacity display caused by non-legitimate devices.