[USB Flash Basic] What is the difference between advertised capacity and usable capacity?

You might notice that a new 64GB USB flash drive, when plugged into your computer, shows a slightly lower usable capacity (e.g., around 59GB). This discrepancy is normal and due to two main reasons:

1. Decimal vs. Binary Measurement:
   • Manufacturers (Decimal): USB flash drive manufacturers define a gigabyte (GB) as 1,000,000,000 bytes (powers of 10). So, a 64GB drive is advertised as 64,000,000,000 bytes.
   • Operating Systems (Binary): Computer operating systems (Windows, macOS, Linux) calculate storage using powers of 2. They use "gibibytes" (GiB), where 1 GiB = 1,073,741,824 bytes.
   • The Math: When your OS reports capacity, it's displaying it in GiB. So, 64,000,000,000 bytes / 1,073,741,824 bytes/GiB ≈ 59.6 GiB (often displayed as 59.6 GB).
2. Formatter and Firmware Space: A small portion of the drive's capacity is reserved for the drive's firmware, file system structures, and controller overhead. This space is not accessible to the user.