1. Short for Gigabyte, GB or GByte by most standards is equal to 1,073,741,824 bytes or 230. However, the IEC defines a GB equal to 109 or 1,000,000,000 bytes. Therefore, a GB could be either of these values. Many hard drive manufacturers and computer manufacturers will define what they consider a Gigabyte to equal in the fine print.
2. A Gb, or Gigabit, is different from a GB; see the Gigabit definition for additional information.