640

640 is a natural number that follows 639 and precedes 641. In Roman numerals it is written DCXL. In binary it is 1010000000 and in hexadecimal 0x280. The number is even and composite, with prime factorization 2^7 × 5.

Mathematically, 640 is a Harshad number in base 10 since the sum of its digits (6 + 4 + 0) is 10 and 640 is divisible by 10. Its divisors include 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 320, and 640.

In land surveying, 640 acres make up a square mile of area, and a standard US township contains 36 such sections. This relationship makes 640 a common unit of area in the United States.

In computing, 640 KB of conventional memory is a well-known figure from early IBM PC architecture. The so-called 640K memory limit has become a widely cited anecdote, though it is often misattributed and misunderstood regarding actual hardware design constraints of the era.

A common display resolution is 640 by 480 pixels, historically associated with the VGA standard. The 640x480 format has appeared in various multimedia and computer graphics contexts and is still referenced in discussions of legacy display modes.