What is a zettabyte (ZB)?
A zettabyte (ZB) is a unit of digital storage in the decimal measurement system, equivalent to 1,000,000,000,000,000,000,000 bytes ($10^{21}$ bytes). The prefix “zetta” originates from the Greek letter “zeta” (), representing the seventh letter of the Greek alphabet, as $10^{21}$ is $10$ to the power of 7 three times. According to IDC’s “DataSphere” report, approximately 64.2 zettabytes of data were created or replicated globally in 2020, though only about 7 ZB of this data was actually stored across all devices and systems.
What is a petabyte (PB)?
A petabyte (PB) is another unit of digital storage, positioned between a terabyte and a zettabyte. One petabyte is equal to 1,000,000,000,000,000 bytes ($10^{15}$ bytes). As an illustration, a petabyte could store about 500 billion pages of ordinary typed text.
The two measurement systems: SI vs IEC
Digital storage units are defined by two measurement systems:
-
SI (International System of Units) - decimal system
- Base-10: 1 kilobyte = 1,000 bytes.
- Prefixes: kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB), petabyte (PB), zettabyte (ZB).
- Primarily used by storage manufacturers for marketing purposes (e.g., hard drive capacities).
-
IEC (International Electrotechnical Commission) - binary system
- Base-2: 1 kibibyte = 1,024 bytes.
- Prefixes: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB), pebibyte (PiB), zebibyte (ZiB).
- Used by operating systems and software for accurate memory/storage allocation.
Note: Operating systems often display storage using IEC units but label them with SI names (e.g., showing “1 GB” when it’s actually 1 GiB), creating widespread consumer confusion about actual storage capacity.
Conversion formulas
Zettabytes to petabytes (SI system)
1 ZB = 1,000,000 PB ($10^{21}$ bytes ÷ $10^{15}$ bytes)
1 PB = 0.000001 ZB
Zebibytes to pebibytes (IEC system)
1 ZiB = 1,048,576 PiB ($2^{70}$ bytes ÷ $2^{50}$ bytes)
1 PiB = 0.00000095367431640625 ZiB
Cross-system conversions
SI to IEC:
1 ZB ≈ 0.8470329472 ZiB
1 ZiB ≈ 1.1805916207 ZB
Practical conversion examples
Cloud storage
1 ZiB of storage converts to 1,048,576 PiB, or approximately 1,180,591.6207 PB.
Financial sector
A bank’s 5 ZB of transaction data needs allocation in 100-PB units, requiring 50,000 such units.
Storage conversion table
| Storage unit | SI system (decimal) | Bytes (SI) | IEC system (binary) | Bytes (IEC) |
|---|---|---|---|---|
| Kilo/kibi | 1 KB = 1,000 bytes | 1,000 | 1 KiB = 1,024 bytes | 1,024 |
| Mega/mebi | 1 MB = 1,000,000 bytes | 1,000,000 | 1 MiB = 1,048,576 bytes | 1,048,576 |
| Giga/gibi | 1 GB = $10^{9}$ bytes | 1e9 | 1 GiB = 1,073,741,824 bytes | 1,073,741,824 |
| Tera/tebi | 1 TB = $10^{12}$ bytes | 1e12 | 1 TiB = 1,099,511,627,776 bytes | 1,099,511,627,776 |
| Peta/pebi | 1 PB = $10^{15}$ bytes | 1e15 | 1 PiB = 1,125,899,906,842,624 bytes | 1,125,899,906,842,624 |
| Zetta/zebi | 1 ZB = $10^{21}$ bytes | 1e21 | 1 ZiB = 1,180,591,620,717,411,303,424 bytes | 1,180,591,620,717,411,303,424 |
Frequently asked questions
How many petabytes are in a zettabyte?
1,000,000 PB in the SI system (1 ZB = $10^{6}$ PB). In the IEC system, 1 ZiB = 1,048,576 PiB.
Why do storage manufacturers use different units than operating systems?
Manufacturers use SI (decimal) units which show larger numbers (1 GB = 1 billion bytes), while computers use IEC (binary) units for precise addressing (1 GiB = 1,073,741,824 bytes). This discrepancy leads to the “missing storage” phenomenon where a 1TB drive shows as ~931GB in Windows.
What is the difference between a pebibyte and a petabyte?
1 PiB (pebibyte) equals 1,125,899,906,842,624 bytes ($2^{50}$), while 1 PB (petabyte) equals 1,000,000,000,000,000 bytes ($10^{15}$). The PiB is about 12.6% larger than PB.
How to calculate how many 100PB storage units are needed for 3.5ZB of data?
Using the SI system:
3.5 ZB = 3.5 × $10^{6}$ PB
Number of units = 3,500,000 PB ÷ 100 PB/unit = 35,000 units
In IEC: 3.5 ZB ≈ 2.9646 ZiB = 3,108,385 PiB → 31,083.85 units (showing why system consistency matters)