ACK
Acknowledge
ControlASCII 6 | Hex 0x06 | U+0006
ACK (code 6) confirms successful receipt of data. In the original teletype protocol, a receiver sent ACK after validating each transmitted block. TCP's acknowledgment mechanism serves the same purpose but operates at the transport layer with sequence numbers rather than a single control character. The ENQ/ACK handshake pattern from the 1960s directly influenced the SYN/SYN-ACK/ACK three-way handshake that TCP adopted in 1981 (RFC 793). Some serial printers still require ACK before accepting the next data block.
ASCII Code
Decimal
6
Hexadecimal
0x06
Octal
6
Binary
0000 0110
Unicode
Code Point
U+0006
Escape
\u0006
UTF-8 Hex
0xE2 0x90 0x86
UTF-8 Binary
111000101001000010000110
UTF-16
0x0006
UTF-32
0x00000006
HTML Entities
Numeric

Hex

How to Type
HTML Entity

Unicode InputU+0006
Source Code Representations
C / Java
"\u0006"CSS
\0006JavaScript
"\u0006"Perl
\x{0006}Python 2
u"\u0006"Python 3
\u0006Ruby
\u{0006}Frequently Asked Questions
What is ASCII code 6?
ASCII code 6 represents the Acknowledge character. In hexadecimal it is 0x06, in binary 0000 0110, and in octal 6. This is a non-printable control character used for device signaling and data transmission control.
How do I type ASCII 6 on a keyboard?
Control characters are typically entered using Ctrl key combinations. For example, Ctrl+F produces ASCII 6 in most terminal emulators. You can also use the HTML entity  in web pages.