1981
1981 is the year the IBM PC was released.
- Odd
- Composite
Where 1981 fits
Why 1981 is special
IBM built it from off-the-shelf parts and licensed rather than owned its operating system, which made compatible machines legal to build. That decision created the PC industry and cost IBM control of it within a decade.
Same number, different meanings
How 1981 is understood across different contexts — never implying one meaning because of another.
- Mathematics
IBM built it from off-the-shelf parts and licensed rather than owned its operating system, which made compatible machines legal to build. That decision created the PC industry and cost IBM control of it within a decade.
- History
In 1981, the first Space Shuttle flew, and the IBM PC was released (North America).
- Finance & economics
IBM built the PC from off-the-shelf parts and licensed rather than owned its operating system, which made compatible machines legal to build. That created the PC industry and cost IBM control of it inside a decade.
1981 is part of
Factors & digit properties
- Divisors (4)
- 1, 7, 283, 1981
- Prime factorisation
- 7 × 283
- Digit sum
- 19
- Digital root
- 1
Representations
- Decimal
- 1981
- Scientific notation
- 1.981 × 10^3
Roman numerals
M C M L X X X I
MCMLXXXI uses the subtractive pair CM: a hundred before a thousand — a thousand minus a hundred.
Binary
1 1 1 1 0 1 1 1 1 0 1
1 × 1,024 + 1 × 512 + 1 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 1,981
Octal
3 6 7 5
3 × 512 + 6 × 64 + 7 × 8 + 5 × 1 = 1,981
Hexadecimal
7 b d
7 × 256 + b × 16 + d × 1 = 1,981
Read as powers of two: 1,024 + 512 + 256 + 128 + 32 + 16 + 8 + 4 + 1 = 1,981.
In historical numeral systems
Egyptian
1 lotus, 9 coils of rope, 8 hobbles, 1 stroke
1 × 1,000 + 9 × 100 + 8 × 10 + 1 × 1 = 1,981. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
3 corner wedges + 3 vertical wedges (sixties place), 1 vertical wedge (units place)
33 × 60 + 1 = 1981. Places are separated by a space on the tablet, with the higher place written first.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Semiprime
Related numbers & connections
The Apple II and the IBM PC, four years apart. The first proved there was a home market and the second made it an industry with interchangeable parts.
View 1977 →Kodak built a digital camera in 1975 and shelved it; IBM built the PC in 1981 and licensed away control of it. Two different ways for an incumbent to lose a market it created.
View 1975 →History
In 1981, the first Space Shuttle flew, and the IBM PC was released (North America).
DocumentedHistoryGeography: North AmericaPeriod: 1981
Finance & economics
IBM built the PC from off-the-shelf parts and licensed rather than owned its operating system, which made compatible machines legal to build. That created the PC industry and cost IBM control of it inside a decade.
DocumentedFinance & economicsPeriod: 1981
Common questions
Is 1981 a prime number?
No, 1981 is not prime.
What are the factors of 1981?
The factors of 1981 are 1, 7, 283, 1981.
What is 1981 in Roman numerals?
1981 in Roman numerals is MCMLXXXI. CM is subtractive: a hundred before a thousand — a thousand minus a hundred. Written additively it would be MDCCCCLXXXI, which Roman inscriptions used freely — the strict subtractive form is a later convention.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026