ASCII 23 — ETB

End of Transmission Block (ETB) marks the end of a data block within a larger multi-block transmission, distinguishing it from EOT which terminates the entire session. ETB enabled large messages to be broken into smaller, independently verifiable blocks — a concept directly paralleling modern packet-based networking where each segment can be acknowledged or rejected independently. This block-based approach allowed selective retransmission of corrupted blocks without resending entire messages, improving both communication reliability and bandwidth efficiency.

Control characters were defined in the original 1963 ASCII standard to manage telecommunications equipment and terminal devices. Unlike printable characters representing visible symbols, control codes perform actions: initiating transmissions, acknowledging received data, triggering device alerts, and structuring information hierarchically. Of ASCII's 128 code points, 33 are designated as control characters (codes 0–31 plus 127), reflecting the standard's deep roots in telegraphy and serial communication systems. While most control codes have fallen out of daily use, several remain essential to modern computing workflows.

In the ASCII encoding table, End of Transmission Block is assigned code point 23 in decimal (0x17 hexadecimal, 027 octal, 00010111 binary). The 7-bit ASCII standard, first published in 1963 by the American Standards Association, defines exactly 128 characters that remain the foundation of text encoding systems worldwide. UTF-8, the dominant encoding on the modern web, is fully backward compatible with ASCII — every ASCII character is encoded as the identical single byte in UTF-8, guaranteeing that End of Transmission Block works reliably across all operating systems, programming languages, and internet protocols.