Understanding data storage units: from exabytes to yottabits
Data storage measurement exists in two distinct systems: the international system of units (SI) using base-10 prefixes and the international electrotechnical commission (IEC) standard using base-2 prefixes. The SI system defines:
- Exabyte (EB) = bytes
- Yottabit (Ybit) = bits
The IEC binary system defines:
- Exbibyte (EiB) = bytes
- Yobibit (Yibit) = bits
Confusion arises because operating systems often report storage in SI units while actually using binary addressing. For example, a drive marketed as “1 TB” (1 trillion bytes) appears as ~931 GiB in Windows.
Conversion formulas
Within SI system (decimal)
Explanation: Multiply EB by 8 to convert bytes→bits, then divide by since 1 yottabit = bits and 1 exabyte = bytes ().
Within IEC system (binary)
Explanation: Multiply EiB by 8 for bytes→bits, then divide by because 1 yobibit = bits and 1 exbibyte = bytes ().
Cross-system conversions
Step-by-step calculation examples
Example 1: Convert 3 exabytes (EB) to yottabits (Ybit) using SI units
Example 2: Convert 5 exbibytes (EiB) to yobibits (Yibit) using IEC units
Example 3: Compare 10 EB (SI) and 10 EiB (IEC) in yottabits
- 10 EB to Ybit:
- 10 EiB to Ybit: First convert EiB→EB: , then to Ybit:
Practical applications
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Data center scaling: A 100 EB storage array (SI) requires bits. In yottabits: .
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Global internet traffic: Annual traffic is ~3.5 ZB (zettabytes, bytes). To express in yottabits:
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IEC in memory manufacturing: A 128 EiB RAM module contains:
Historical context
The IEC introduced binary prefixes in 1998 to resolve ambiguity. Before this, “exabyte” ambiguously meant either bytes or bytes—a 15.3% difference. This caused legal disputes, such as in 2003 when consumers sued hard drive manufacturers over capacity discrepancies.
Technical considerations
- Accuracy: SI conversions are exact; IEC involve powers of 2.
- Storage media: SSDs/NAND flash typically use SI units, RAM uses IEC.
- Network vs. storage: Network bandwidth (e.g., 100 Gbit/s) uses bits, storage capacity uses bytes.
Frequently asked questions
What’s the difference between Ybit and Yibit?
Yottabit (Ybit) is bits (SI), while yobibit (Yibit) is bits (IEC). 1 Yibit ≈ 1.2089 Ybit—a 20.89% difference.
How to convert 25 EB to EiB?
Why do operating systems show less storage than advertised?
A “1 TB” drive uses SI units ( bytes), but OSes display in IEC units: .
Is internet bandwidth measured in SI or IEC units?
Bandwidth (e.g., 10 Gbit/s) universally uses SI units. 1 Gbit/s always means bits per second.
How many EiB equal one Yibit?
1 Yibit = bits = bytes = bytes. Since 1 EiB = bytes:
Common mistakes to avoid
- Using SI prefixes for memory (e.g., “512 GB RAM” should be “512 GiB”)
- Confusing bits (transmission) with bytes (storage)
- Assuming (1,000 vs 1,024) at exascale—the gap compounds exponentially.