ASCII 1
ASCII 1 is Start of Heading — the control character SOH.
Every representation
| Character | SOH (not printable) |
| Name | Start of Heading |
| Decimal | 1 |
| Hexadecimal | 0x01 |
| Octal | 0001 |
| Binary | 00000001 |
| HTML entity |  |
| Escape sequence | \x01 |
| Unicode | U+0001 |
| Keyboard | Ctrl+A |
| Group | Control character |
What it is for
Marked the beginning of a message header in teleprinter protocols. Survives in a few industrial and financial protocols — FIX messages use it as a field separator.
Where the number comes from
Codes 0 to 31 were reserved for control: instructions to a teleprinter rather than characters to print. Code 1 is Ctrl+A because the Ctrl key was originally wired to clear the top two bits of whatever you typed, mapping the letter A at 65 down to 1.
Frequently asked questions
What is ASCII 1?
Start of Heading (SOH), a control character. In hexadecimal it is 0x01, in octal 0001, and in binary 00000001.
How do I type ASCII 1?
Press Ctrl+A in a terminal. In a string literal you can write it as \\x01 in most languages.
Is ASCII 1 printable?
No. Codes 0 to 31 and 127 are control characters — they were instructions to a teleprinter rather than marks on paper, and most terminals show nothing for them.
Nearby codes
- ASCII 0 — NUL
- ASCII 2 — STX
- ASCII 3 — ETX
- ASCII 4 — EOT
- ASCII 5 — ENQ
- ASCII 6 — ACK
- ASCII 7 — BEL
- ASCII 8 — BS
Full ASCII table · Text to binary converter · Number base converter