1,024

In 1024, the Salian dynasty took the German throne on the extinction of the Ottonian line (Central Europe).

A drive sold as 1 terabyte holds a trillion bytes, and an operating system reporting in binary units divides by 1,024 three times and shows about 931. Neither figure is wrong; they count in different bases.

1024-bit RSA keys were the ordinary standard for public-key cryptography into the 2000s and are now considered inadequate: NIST withdrew approval for them after 2013 and public certificate authorities stopped issuing them. Nothing about the key length changed — what changed is that factoring capability improved steadily enough for a fixed size to become a moving deadline, which is why key sizes are quoted with a date rather than as permanent guidance.

On Unix-derived systems, binding a listening socket to a port below 1024 has historically required superuser privileges, which is why web servers on port 80 or 443 start as root and drop privileges immediately afterwards. The range is called the well-known or system ports and is administered by IANA. The boundary is 2¹⁰ for no reason beyond it being a convenient round figure in binary — the security value of the convention rests on the operating system enforcing it, not on the number.

1024 × 768 — XGA, introduced by IBM in 1990 — was the default assumption web designers built to for roughly fifteen years, and it remained the most common screen resolution in use well into the 2000s. Its 4:3 shape is why pages of that era were laid out in a fixed-width column: the designer knew almost exactly how wide the reader's window would be, which is a certainty responsive design deliberately gave up.

Early computing treated 1024 bytes as one kilobyte, conflicting with the SI meaning of kilo- (exactly 1000). The IEC introduced the binary prefix kibibyte (KiB) for 1024 bytes in 1998; the older kilobyte usage persists informally but is formally superseded.

The IEC's 1998 binary prefixes — kibi, mebi, gibi, tebi — exist so that 1,024 bytes can be named without borrowing 'kilo' from SI, where it means exactly 1,000. Adoption has been uneven: Linux and macOS report storage in decimal units, Windows reports the binary value while labelling it with the decimal prefix, and drive manufacturers sell in decimal. All three are internally consistent, which is precisely why the discrepancy never resolves itself.

A set of ten things has exactly 1,024 subsets, because each item is independently either in or out and 2¹⁰ = 1,024. The same arithmetic answers a family of questions that look unrelated: ten coin tosses have 1,024 outcomes, a ten-question yes/no form has 1,024 possible completions, and a row of ten switches has 1,024 settings. 1,024 is also 4⁵ and 32².

1024 is 2¹⁰ — the closest power of two to 1000, which is the reason it was adopted as computing's informal 'kilobyte'.