Numberwise

640

640 kilobytes was the conventional memory limit of the original IBM PC architecture.

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Where 640 fits

Where 640 fits: Mathematics, Related numbersMathematics: Harshad (Niven) number. Related numbers: 1024.MathematicsHarshad (Niven) numberRelated numbers1024640
640 connects to 2 worlds: mathematics, related numbers.

Why 640 is special

The limit was real: the 8088's one-megabyte address space reserved everything above 640 KB for hardware, so software got what was left. The famous quotation about 640K being enough for anybody is attributed to Bill Gates, who has denied saying it, and no contemporary source for it has been found.

Factors & digit properties

Divisors (16)
1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 320, 640
Prime factorisation
2^7 × 5
Digit sum
10
Digital root
1

Representations

Decimal
640
Binary
1010000000
Octal
1200
Hexadecimal
280
Roman numeral
DCXL
Scientific notation
6.400 × 10^2

Other mathematical patterns

  • Abundant number
  • Harshad (Niven) number

Related numbers & connections

Connection
The original PC could address 1,024 KB and reserved everything above 640 KB for hardware, leaving software the remainder. The limit was a consequence of the memory map, not of the processor's arithmetic.

The original PC could address 1,024 KB and reserved everything above 640 KB for hardware, leaving software the remainder. The limit was a consequence of the memory map, not of the processor's arithmetic.

View 1024 →

Other connections

  • is associated with1024
    why?

    Strength 0.50, confidence "high".

How is 640 connected to another number? →

Technology & computing

  • The 8088 could address one megabyte and the architecture reserved everything above 640 KB for hardware, so software received what was left. The limit was genuine and shaped a decade of DOS programming. The famous remark that 640K ought to be enough for anybody is attributed to Bill Gates, who has denied it, and no contemporary source has ever been produced.

    DocumentedTechnology & computing

Common questions

Is 640 a prime number?

No, 640 is not prime.

What are the factors of 640?

The factors of 640 are 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 320, 640.

What is 640 in Roman numerals?

640 in Roman numerals is DCXL.

About this page's data

Mathematical facts:computed directly from the number's value — nothing to source or verify externally.

Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.

Last reviewed: 3 August 2026