The at sign was not born on the internet. The hash is older than the telephone. And the power button you press every day has sat inside an international standard since 1973. Look at any screen or keyboard and you are looking at signs borrowed from printing, musical notation, medieval arithmetic and old handwriting.
Here is my starting point, and it runs through everything below: almost no computing symbol was designed for computing. Know where each sign comes from and you stop guessing why it behaves the way it does. The tour comes in two parts. First the icons on your devices, then the signs on your keyboard, each with its etymology and the story that put it there.
The icons on your devices: power, USB, Bluetooth and Wi-Fi
The power symbol (⏻)
The popular story says the power button comes from fusing a 1 (on) and a 0 (off) from the binary system. The documented version is different. The symbol was collected in the catalogue of graphical symbols of the International Electrotechnical Commission (IEC 60417) in 1973, under the name «standby». Reading a 1 and a 0 into it fits neatly, but the standard never claimed it. That document fixed three signs: a line inside a circle for on and off, a bare line for on, and a bare circle for off. Unicode later gave them characters of their own.
The USB trident
The USB logo is a trident, and the most repeated reading says it imitates Neptune’s. Its three points are capped by a circle, a square and a triangle, and between them they stand for the many peripherals the standard can connect, from keyboards to the different types of USB. Here honesty pays. The USB Implementers Forum, which licenses the logo, does not document that meaning anywhere. It is a popular reading with no official explanation behind it.
Bluetooth’s runes
The Bluetooth symbol is a bind rune that fuses two letters of the young futhark: Hagall (ᚼ) and Bjarkan (ᛒ). They are the initials of Harald «Bluetooth» Gormsson, the tenth-century Danish king who united Denmark and Norway. The Bluetooth SIG itself says the name started as a temporary codename Jim Kardach of Intel proposed in 1997, and that it stuck before anyone found the time to change it. As for the blueberry that supposedly stained one of his teeth, that part belongs to folklore. The official version speaks of a dark tooth.
Wi-Fi waves and the play triangle
The Wi-Fi symbol is the youngest of the family. It arrived with the brand in the 2000s and stands for the waves of a radio signal. Its virtue is that it grades: more arcs mean a stronger signal. The play triangle spread with cassette tapes in the 1960s and suggests forward motion along a horizontal line. The pause icon is usually tied to the caesura of musical notation.
Keyboard symbols: what each one means
These are the real stars. Not one of them was invented for programming, yet all of them ended up on the keyboard because they already lived on typewriters and in books.
| Symbol | Name | Unicode name | Where it comes from |
|---|---|---|---|
@ |
At sign | COMMERCIAL AT | An Arabic unit of weight, later used in trade |
# |
Hash or number sign | NUMBER SIGN | An English abbreviation of «number» |
/ |
Forward slash | SOLIDUS | The stroke of handwritten fractions |
\ |
Backslash | REVERSE SOLIDUS | Invented for the ASCII code, in 1961 |
~ |
Tilde | TILDE | A medieval abbreviation, the squiggle over the Spanish ñ |
| |
Vertical bar or pipe | VERTICAL LINE | A mathematical and logical symbol |
& |
Ampersand | AMPERSAND | A ligature of the Latin word et |
* |
Asterisk | ASTERISK | From the Greek asteriskos, «little star» |
^ |
Caret | CIRCUMFLEX ACCENT | A proofreading mark: something is missing here |
% |
Percent sign | PERCENT SIGN | An Italian abbreviation of per cento |
The at sign (@): from a unit of weight to the king of email
The symbol is ancient, and its name gives it away. In Spanish it is «arroba», from the Andalusian Arabic arrúb‘ and, before that, from classical Arabic rub‘, «a quarter». That was a unit of weight of around 11.5 kilograms. The leap to fame came in 1971, when the programmer Ray Tomlinson picked the sign, present on keyboards but rarely used, to separate the user’s name from the machine’s in email addresses. The Internet Hall of Fame records it that way. Today its exact shape is fixed by RFC 5322, the document that defines the format of email messages.
The hash (#): number sign, hash and pound
In English the sign drags several names at once: number sign, hash, pound sign. That causes real confusion, because the British pound is the pound sterling (£), something else entirely. Its formal Unicode name is NUMBER SIGN. Today it comments out lines of code in Python or Bash, marks anchors in web addresses and tags posts on social media. The shape is the same everywhere, though the names pile up the moment you cross a border.
The slashes (/ and \): from the Roman solidus to the Windows C:
The forward slash (/) is SOLIDUS in Unicode. It was the stroke that separated the numerator from the denominator in handwritten fractions. In computing it became the path separator of Unix-like systems and, later, a central piece of web addresses: RFC 3986 defines the syntax of URLs and uses the slash to separate each segment of the path.
The backslash (\) did not exist on almost any keyboard or code before 1961. The engineer Bob Bemer proposed it for the ASCII code, with an eye to combining / and \ as logical operators in the ALGOL language, exactly as he recounted. The Computer History Museum keeps that account in his biography. Years later the DOS operating system adopted it as a path separator, and from there it travelled to every version of Windows. That is why Windows paths run opposite to those of the operating systems descended from Unix, a slip-up you make every day at a terminal.
The tilde (~), the vertical bar (|) and the caret (^)
The tilde (~) comes from the Latin titulus, «sign», and in Spanish it is the squiggle that gives the ñ. On Unix it was adopted for the home folder. Type cd ~ and you are back home, because the shell expands the shortcut, as the GNU Bash manual documents.
The vertical bar (|), or pipe, is the symbol of the pipeline in the terminal. It connects the output of one program to the input of the next, an idea that grew into the Unix habit of chaining small tools. The Bash reference shows how. The caret (^) started life as a proofreading mark in manuscripts. From the Latin caret, «it is missing», it signalled that something had to be inserted right there. In programming it ended up standing for exponentiation and the logical XOR operator.
The ampersand (&), the asterisk (*) and the percent sign (%)
The ampersand (&) is the ligature of the Latin word et, «and». Hence its shape. Its English name comes from the way children recited the alphabet, which used to end with «and per se and», as Keith Houston recounts in Shady Characters. In programming languages it is the logical conjunction operator, the address-of operator in C and the parameter separator in URLs.
The asterisk (*) takes its name from the Greek asteriskos, «little star». Ancient scholars used it to mark doubtful passages. From there it moved into computing: a wildcard in the file system, a quantifier in regular expressions, multiplication in arithmetic and pointers in C.
The percent sign (%) comes from the Italian abbreviation of per cento, written with a p, a c and a small circle. Those two «zeros» most people see are actually the letter o that closed the abbreviation. Over the centuries the stroke simplified into today’s symbol, as the typography historian Keith Houston documents in Shady Characters.
From scribes to ASCII: how old signs became code
Many of these signs existed centuries before there were computers. They are old acquaintances of printers, scribes and mathematicians. The great leap came in 1963 with the ASCII code, the set of 128 characters that gave every sign a number and a stable name, one more milestone in the history of computing. There the # was fixed as NUMBER SIGN, the ~ as TILDE and the @ as COMMERCIAL AT. The Unicode standard later inherited those names and added the modern symbols, such as the power icons.
Recycling signs that already existed had an unavoidable side effect: the same symbol means different things depending on where you are. The slash / separates paths in Linux and macOS, but on Windows that job falls to the backslash \. The tilde ~ is the home folder on Unix and an approximation mark in mathematics. And the hash # comments out a line in Python or Bash, while in C it serves the preprocessor. Call it the fingerprint of the decades that carried each sign to where it is now.
Why it is worth knowing these symbols
Because they save time and mistakes. Know that the vertical bar | is not a letter «l» or a «1», and that ~ means «home folder», and you head off silly errors when you copy a command. It also helps you read a technical manual without stumbling over the terminology: when a document talks about a solidus, a tilde or a pipe, it means these old acquaintances. And they make a good talking point at any dinner, as readers of our computing curiosities already know. If you want to go one step further, the story of how the keys themselves were arranged is told in the origin of the QWERTY keyboard layout.
Carry one idea out of all this. Computing did not invent almost any of its signs. It gave them a second job. Follow that journey, from an Arabic weight to a Viking rune, and the keyboard stops looking like a random collection of scribbles. Pick one key today, the @ or the |, and trace it back to its source. You will never type it the same way again.
Frequently asked questions
Is the power symbol a 1 and a 0 fused together?
It is the most popular reading, but the documented origin is different. The symbol was collected in the IEC 60417 standard, in 1973, under the name «standby». The interpretation of the 1 (on) and the 0 (off) fits well, but the standard itself does not record it.
Why do Windows paths use a backslash and Linux a forward slash?
Out of inheritance. The forward slash came from handwritten fractions and was adopted by Unix. The backslash was proposed by Bob Bemer for the ASCII code in 1961, and the DOS system chose it as a path separator. From there it travelled to every version of Windows.
Where does the @ symbol come from?
It began as a unit of weight in Arabic-speaking lands, around 11.5 kilograms, and was later used in trade, which is why Unicode names it COMMERCIAL AT. In 1971 Ray Tomlinson chose it for email addresses because it was on the keyboard but rarely used.
What does the tilde (~) mean in a Linux path?
It represents the user’s home folder. Typing cd ~ is the same as going to your home directory, and the command shell expands it automatically.
Why is the Bluetooth logo two runes?
It is a bind rune that fuses Hagall (ᚼ) and Bjarkan (ᛒ), the initials of Harald «Bluetooth» Gormsson, the tenth-century Danish king who united Denmark and Norway and gave the technology its name.