The CWI punched tape collection

Rows of tiny holes on paper once held entire programs and documents: punched tape was the lifeline of early computing. Today, CWI is preserving and sharing its own historic tapes from the Mathematisch Centrum, now digitized and made accessible online.

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Before USB sticks, hard drives or even floppy disks, early computers stored data in a very different way: on punched tape. This paper medium, used from the 1950s to the 1970s, played a key role in programming, data exchange, and automation.

At CWI, we are preserving a unique collection of punched tapes originally used at our institute (then called Mathematisch Centrum), which are associated with early Dutch computers such as the Electrologica X1. As part of a long-term digital heritage project, we have carefully read, decoded and archived the contents of over 160 tapes. The collection contains tapes with ZEBRA Simple Code, X1 handcode, Algol60 source code for (mostly) numerical functions, and several text documents.

Five hole and eight hole perforated paper tape as used in early telegraph and computer applications. Picture: Ted Coles, Wikimedia Commons.

What is punched tape?

In the history of computing, punched tape played an important role. Punched tape is a long strip of paper that is perforated with 5-8 holes as shown below. Each 'frame' (an ordered list of 5-8 of holes perpendicular to the length of the tape) represents a single symbol. All tapes also have sprocket holes (the line of smaller holes on both tapes below) that serve to guide the reading/writing device.

Picture: Five hole and eight hole perforated paper tape as used in telegraph and computer applications. Picture: Ted Coles (Wikimedia Commons)

Friden FlexoWriter

One way of reading and writing punched tape is using a Friden FlexoWriter, a typewriter-like device that could produce tapes by typing on the keyboard, or printing tapes by reading a tape.

Friden FlexoWriter

Friden Flexowriter in the UvA Computermuseum. Picture: CWI/J. Borst

Friden Flexowriter in the UvA Computermuseum. Picture: CWI/J. Borst

X1

Historical picture of the former MC's X1 with Geert Rolf. Photo taken in 1976/1977 at the HTS Amsterdam. Picture: Geert Rolf.

Historical picture of an X1 with Geert Rolf. Picture: Geert Rolf

Storing information

Punched tape was, for instance, used for storing the following information:

  • text documents
  • machine code
  • program source code
  • program input data
  • program output data
  • intermediate results between program executions.

For the earliest computers, punched tape was the only external storage medium and it was therefore the only way to enter programs or data.

The punched tapes in the CWI collection span the period 1955-1965 and were mostly, but not exclusively, used on the Electrologica X1 computer. The collection contains tapes with 5 or 7 holes.

All 5 hole tapes are binary and are not directly human readable. All 7 hole tapes were produced by a Flexowriter and contain either Algol 60 programs or text documents.

Categories

The tapes can be subdivided into the following categories:

For each tape there are several files available:

  • a file with the raw data (with extension .5 for 5 hole and .7 for 7 hole tapes);
  • a text file derived from the raw data (extension .txt).

Original files

Would you like to study the original files?

See the complete list of 165 punched tapes in the CWI repository.

The programs used for decoding and conversion are available in the CWI repository.

The machine shown here is a PDP-11/10, popular in the 1970s and 1980s and widely used for research and industry. This particular PDP-11/10 belonged to Geert Rolf. Picture: Geert Rolf.

Making the collection accessible

The initial inventory of the tapes was made by Paul Klint, who also wrote this introduction. Together with Geert Rolf, intern at MC back in 1980/1981, the tapes were read in on Geert's PDP11/10. Some tapes could not be read because they were either too large for the tape reader or they were damaged and could not be read. They are marked as Not Processed (n) in the inventory.

The 7 hole tapes use FlexoWriter code. A readable version of these tapes was produced using the rf program written by Edo Dooijes (Computer Museum, University of Amsterdam). X1 hand code was converted by the program x1hand, written by Geert Rolf. The 5 hole tapes were made readable as a decimal dump in a text file.

The machine shown in the picture is a PDP-11/10, popular in the 1970s and 1980s and widely used for research and industry. This particular PDP-11/10 belonged to Geert Rolf. Picture: Geert Rolf.

Rolled-up punched tape in the PDP-11

A roll of punched tape being read on Geert Rolf’s PDP-11/10, as part of the project to digitize and preserve CWI’s historic tape collection.

Rolled-up punched tape in the PDP-11. Picture: Geert Rolf.

See also the news item 'CWI preserves historic punched tape collection' (October 2025).

Acknowledgements

CWI is grateful to Paul Klint and Geert Rolf for their contributions to this project: reading the tapes and converting the data.

Punched tape project: CWI Fellow Paul Klint, then-CWI director Ton de Kok, Geert Rolf and Vera Sarkol (CWI Library), 10 April 2025. Picture: CWI/P. Roberts.
Punched tape project: CWI Fellow Paul Klint, then-CWI director Ton de Kok, Geert Rolf and Vera Sarkol (CWI Library), 10 April 2025. Picture: CWI/P. Roberts.