Materiality has often been a neglected factor in discussions of digitally encoded information. While a lot of early works in media studies suffered from this shortcoming, questions regarding the materiality of digital technology and artefacts have slowly gained prominence in recent debates. Matthew Kirschenbaum’s concept of “forensic” and “formal” materiality has proven particularly useful to the study of digital artefacts, differentiating the (routinely overlooked) physical existence of digital data from their (commonly discussed) logical character. However, analyses concerning the materiality of digital artefacts are often one-sided, focussing on the physicality of the medium in which digital data are inscribed. To counter this bias, I present the concept of a ‘reciprocal materiality’ of digital data: It is not only that digital data are always inscribed in some material substrate (Kirschenbaum’s ‘forensic’ dimension of data); conversely, the materiality of the medium inscribes itself into the structure of digital data (its ‘formal’ level). The ‘body of code’ is shaped by the material framework it inhabits. I will illustrate this using as an example one of the most important encoding schemes in the history of digital technology: the American Standard Code for Information Interchange (ASCII). A ‘close reading’ of the technical specifications of ASCII - a standard designed in the early 1960s to work across multiple technological platforms - will reveal the extent to which this code incorporates the materiality of media such as punched tape and teletype terminals.