MB vs. GB: Understanding Decimal vs. Binary Storage

Have you ever bought a brand-new 1 Terabyte (1 TB) SSD or hard drive, plugged it into your Windows PC, and felt cheated when File Explorer displayed only 931 GB of usable storage?

Your hardware is not defective, and no manufacturer stole your space. This common discrepancy comes down to a fundamental conflict between two measurement systems: Decimal (SI base 10) and Binary (IEC base 2).

The Missing Gigabytes Mystery

Drive manufacturers measure storage in decimal powers of 10:

• 1 Kilobyte (KB) = 1,000 Bytes (10^3)
• 1 Megabyte (MB) = 1,000,000 Bytes (10^6)
• 1 Gigabyte (GB) = 1,000,000,000 Bytes (10^9)
• 1 Terabyte (TB) = 1,000,000,000,000 Bytes (10^12)

However, operating systems like Microsoft Windows address memory in binary powers of 2:

• 1 Kibibyte (KiB) = 1,024 Bytes (2^10)
• 1 Mebibyte (MiB) = 1,048,576 Bytes (2^20)
• 1 Gibibyte (GiB) = 1,073,741,824 Bytes (2^30)
• 1 Tebibyte (TiB) = 1,099,511,627,776 Bytes (2^40)

When Windows divides 1,000,000,000,000 bytes by 1,073,741,824 (GiB), the math yields: 931.32 GiB (which Windows simply labels as "GB").

SI Decimal (1000) vs. IEC Binary (1024) Standards

In 1998, the International Electrotechnical Commission (IEC) introduced prefix standards (Kibi, Mebi, Gibi, Tebi) to eliminate ambiguity:

Digital Units Comparison Chart

Bits (b) vs. Bytes (B): Network vs. Storage

Another frequent point of confusion is lowercase "b" (bits) versus uppercase "B" (bytes).

• 1 Byte (B) = 8 Bits (b)
• Internet service providers advertise bandwidth speeds in Megabits per second (Mbps).
• File download progress is measured in Megabytes per second (MB/s).
• Therefore, a 100 Mbps internet connection downloads at a maximum real-world speed of 100 / 8 = 12.5 MB/s.